Bally/Stern

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1 Introduction

Bally first started to experiment with solid state in the mid 70s with a couple conversions of EM games, Flicker and Bow & Arrow. Flicker's control system was designed by Jeff Frederiksen of Dave Nutting Associates, a Bally think-tank. This board utilized the Intel 4004 microprocessor. One prototype was built and was re-discovered in 1998. The Bow & Arrow system of which 17 were eventually built more closely resembles what actually ended up in the production games starting with Freedom. This boardset was designed by a Bally engineer named Doug MacDonald. There are at least two revisions of the prototype run's software in existence.

The early circuit boards were fabricated by a company called Universal Research Laboratories (URL). URL was purchased by Sam Stern as part of his strategy in acquiring the assets of the defunct Chicago Coin; it is this connection that enabled Stern to use essentially the same hardware for their solid state games as Bally. The software is remarkably similar as well, although Bally was more apt to use a "set" of operating system roms (the U6 chip) for several games, whereas Stern opted to custom-compile their roms for each game, or at most, pairs of games.

The core system consists of:

• A transformer to produce various AC voltages from line voltage
• A rectifier board to convert those AC voltages to DC and provide fuse protection
• A solenoid driver/voltage regulator board to regulate/filter the DC voltages and provide switching for solenoids
• A lamp driver board to switch up to 60 lamps on/off

Optional components added to the system at later dates include:

• Various sound boards, providing various type of sounds from simple tones, to background sound, to complex speech and sounds
• Auxiliary lamp driver boards, to provide control for more than 60 lamps
• Solenoid expander boards to allow more than 15 controllable momentary solenoids to be connected

Bally -35 Board Set

Stern M-200 Board Set

Bally Goldball special driver/voltage board

2 Games

A list of solid state games by system and manufacturer (including those that aren't necessarily pinball). Source: http://www.ipdb.org

2.1 Bally

Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Freedom	AS-2518-17	AS-2518-18	AS-2518-14	Chimes
Night Rider	AS-2518-17	AS-2518-18	AS-2518-14	Chimes
Black Jack	AS-2518-17	AS-2518-18	AS-2518-14	Chimes
Evel Knievel	AS-2518-17	AS-2518-18	AS-2518-14	Chimes
Eight Ball	AS-2518-17	AS-2518-18	AS-2518-14	Chimes
Power Play	AS-2518-17	AS-2518-18	AS-2518-14	Chimes
Mata Hari	AS-2518-17	AS-2518-18	AS-2518-23	Chimes
Strikes & Spares	AS-2518-17	AS-2518-18	AS-2518-23	Chimes
Black Jack	AS-2518-17	AS-2518-18	AS-2518-23	Chimes
Lost World	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32
The Six Million Dollar Man	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32
Playboy	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32
Voltan	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32
Supersonic	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32
Star Trek	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Paragon	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50
Harlem Globetrotters	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50
Dolly Parton	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50
Kiss	AS-2518-35	AS-2518-49	AS-2518-23	AS-2518-50	Auxiliary Lamp Driver AS-2518-43
Future Spa	AS-2518-35	AS-2518-49	AS-2518-23	AS-2518-51	Auxiliary Lamp Driver AS-2518-43
Space Invaders	AS-2518-35	AS-2518-49	AS-2518-23	AS-2518-51	Auxiliary Lamp Driver AS-2518-52
Nitro Groundshaker	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Silverball Mania	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Rolling Stones	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Mystic	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Hotdoggin	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Viking	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Skateball	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Frontier	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51
Xenon	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-56	Auxiliary Lamp Driver AS-2518-52, Vocalizer module AS-2518-58
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Flash Gordon	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61	Early games used the AS-2518-56 sound board
Eight Ball Deluxe	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A	Auxiliary Lamp Driver AS-2518-52
Fireball II	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A
Embryon	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A
Fathom	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A
Medusa	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A
Centaur	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B	Reverb AS-2518-81, Auxiliary Lamp Driver AS-2518-43
Elektra	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B
Vector	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B
Spectrum	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B	Uses a second AS-2518-23 for lamps (2 total in game)
Speakeasy	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-51
Rapid Fire	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B
Granny and the Gators	AS-2518-133	AS-2518-132	AS-2518-107 (combo lamp and solenoid driver)		Vidiot AS-2518-121
Mr. & Mrs. Pacman	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B
Baby Pac-Man	AS-2518-133	AS-2518-132	AS-2518-107 (combo lamp and solenoid driver)		Vidiot AS-2518-121
Eight Ball Deluxe Limited Edition	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61	Auxiliary Lamp Driver AS-2518-52
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
BMX	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-51
Centaur II	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B	Reverb AS-2518-81, Auxiliary Lamp Driver AS-2518-43
Goldball	AS-2518-35	AS-2518-54	AS-2518-147 (combo lamp and solenoid driver)	AS-2518-51
X's & O's	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045 (A080-91603-B000)
Kings of Steel	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045 (A080-91603-B000)
Black Pyramid	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045
Eight Ball Deluxe Classic	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61	Auxiliary Lamp Driver AS-2518-52
Fireball Classic	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045
Cybernaut	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045

2.2 Stern

Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Pinball	M-100			Chimes
Stingray	M-100			Chimes
Stars	M-100			Chimes
Memory Lane	M-100			Chimes
Lectronamo	M-100			SB-100
Wild Fyre	M-100			SB-100
Nugent	M-100			SB-100
Dracula	M-100			SB-100
Trident	M-100			SB-100
Hot Hand	M-100			SB-100
Magic	M-100			SB-100
Cosmic Princess	M-100			SB-100
Meteor	M-200			SB-300
Galaxy	M-200			SB-300
Ali	M-200			SB-300
Game Title	MPU	Power Supply	Lamp driver	Sound	Add'l boards
Big Game	M-200			SB-300
Seawitch	M-200			SB-300
Cheetah	M-200			SB-300
Quicksilver	M-200			SB-300
Stargazer	M-200			SB-300
Nine Ball	M-200			SB-300
Iron Maiden	M-200			SB-300
Viper	M-200			SB-300
Dragonfist	M-200			SB-300
Cue	M-200			SB-300
Flight 2000	M-200			SB-300	Voice module VS-100
Free Fall	M-200			SB-300	Voice module VS-100
Lightning	M-200			SB-300	Voice module VS-100
Split Second	M-200			SB-300	Voice module VS-100
Catacomb	M-200			SB-300	Voice module VS-100
Orbitor One	M-200			SB-300	Voice module VS-100

3 Technical Info

3.1 The Wiring Color Code

The Bally color coding system is a carry over from the EM era. Either one color or a two color code is used for every wire. The first number is the wire's insulation color, while the second number is the trace color, if one is used. The traces on the wire can either be dashes or stripes. Either type of marking has the same coding designation. An example of a wire with the code 15, would be a red wire with a white trace. A black wire with no trace would be code 80. If a wire color is used more than once, a "-" and the "nth" time the color is used is added as a suffix to the color code. An example of this is a red wire with white traces used a second time. The code for the wire would be 15-1.

Conversely, Stern never adopted a color coding system. Instead, the wire color was marked accordingly in the associated documentation, (ie. a white wire with a blue trace is referred to as W-BLU, red with yellow is R-Y, black is just B, etc.).

Below is the Bally color chart.

	1	2	3	4	5	6	7	8	9	0	Jumper
Color	Red	Blue	Yellow	Green	White	Brown	Orange	Black	Gray	No Trace	Jumper

3.2 Connector Designations

All Bally / Stern machines have a common naming convention for all of the connectors in the game. A specific connection uses two parts - a prefix and a suffix. The prefix is the board number, and the suffix is the connection on the board. When referencing a specific connector pin within a housing, a dash follows the connection number. For example, the connector pin for the coin door self test switch signal on the CPU board is A4J3-1. A single connection, in this case the key on a display, for the player 2 display would be 2A1-14. The same connection on a player 3 display would be 3A1-14.

The following boards are assigned the same numbers throughout Bally / Stern games.

• Lamp Driver Board - A5
• MPU Board - A4
• Solenoid Driver Board - A3
• Transformer Module / Rectifier Board - A2
• Displays - A1

3.2.1 Molex Crimper Styles

Hand held crimpers for Molex style pins come in several styles, and as always, you get what you pay for. Cheaper types sacrifice ease of use, and quality of crimp and durability of the tool. A professional Molex crimper can cost more than $300, and is not necessary to do a excellent job of replacing the pins on a pinball machine. The cheapest type is the Waldom crimper for around $15, and is not recommended. The tool requires that you crimp twice, first for the bare wire, then for the insulation, increasing the chances of a bad crimp. Better is the $25 Sargent 1028-CT tool, which also must be crimped twice, but has better quality and is the only choice for .084 pins. Best are the Sargent type tools (3136-CT shown below) at about $95. These crimpers may have a holder for the pin, and also crimp BOTH the wire and insulation crimp at the same time, reducing the chances of a bad crimp. These tools are specific for the type of connector, whether that is a .156, .062, .100 pin. The .100 crimper does NOT have a pin holder. Replacement parts are also available for this style.

Pictured from left to right, Sargent .100 crimper w/o holder, Waldom universal crimper, Sargent 1028-CT, and Sargent 3136-CT for.156 pins shown with holder

3.3 Proprietary Numbers on Chips

Some Bally IC chips are marked with proprietary Bally part numbers, and no other markings are present. Below is a list of some of the most common chips found on Bally boards, and the more commonly referred to chip.

• 620-28 - 6800 CPU chip
• 620-29 - 6820 PIA chip
• 620-30 - 6810 RAM chip
• 620-37 - 14514 / 4514 CMOS 4-Bit Latch / 4-to-16 Line Decoder chip
• 620-38 - 14534 / 4543 CMOS BCD-to-Seven-Segment Latch / Decoder / Driver chip
• 620-39 - 74L154 4 to 16 decoder chip (can sub with 74HCT154)
• 620-125 - 6808 CPU chip

3.4 Switch Matrix

Bally / Stern 5 x 8 Switch Matrix

The Bally / Stern switch matrix is a 5 x 8 matrix consisting of a maximum of 40 switches. There are a total of 5 switch strobes, (starting with 0, ending with 4), and 8 switch returns, (starting with 0, ending with 7). The numbering convention for the switches is to start at 01, increase by 1 in the same strobe, and continue consecutively to 40. To isolate the switches, a 1N4148 diode or a 1N4004 diode is placed across the switch itself. Not every switch in the matrix is used on every Bally / Stern game.

Although rare, Bally did add a 6th strobe (strobe 5) for some games, such as Medusa and Spectrum.

Connections for the switch matrix originate from the two connectors located on the right side of the CPU board. Connector A4J3 is used for all the switches on the coin door, the ball roll tilt, and the pendulum tilt. While connector A4J2 is for all of the switches on the playfield.

	Strobe 0 (A4J2-1 / A4J3-2)	Strobe 1 (A4J2-2 / A4J3-3)	Strobe 2 (A4J2-3)	Strobe 3 (A4J2-4)	Strobe 4 (A4J2-5)	Strobe 5 (When Used) (A4J4-5)
Return 0 (A4J2-8 / A4J3-9)	01	09	17	25	33	41
Return 1 (A4J2-9 / A4J3-10)	02	10	18	26	34	42
Return 2 (A4J2-10 / A4J3-11)	03	11	19	27	35	43
Return 3 (A4J2-11 / A4J3-12)	04	12	20	28	36	44
Return 4 (A4J2-12 / A4J3-13)	05	13	21	29	37	45
Return 5 (A4J2-13 / A4J3-14)	06	14	22	30	38	46
Return 6 (A4J2-14 / A4J3-15)	07	15	23	31	39	47
Return 7 (A4J2-15 / A4J3-16)	08	16	24	32	40	48

It is worth mentioning that the self test switch, which is located on the inside of the coin door and used to enter tests, audits, and bookkeeping, is not part of the switch matrix. A single signal is sent to the self test switch from the U10 PIA on the CPU board via connection A4J3-1, and returned to ground via a connection A3J2-7 on the solenoid driver board.

Also, the switch commonly referred to as "switch 33" on a Bally or Stern CPU board, and used to reset audits and bookkeeping, is not part of the switch matrix either. This switch receives a signal from the 6800 CPU chip, and when closed, sends the signal to ground. Starting with the first MPU-200 Stern game, Meteor, Stern added a second switch to the inside of the coin door to serve the purpose of remotely resetting audits and bookkeeping. The signal for this secondary switch is tied to the input line of switch 33, and leaves the CPU board via connection A4J3-5. Its return line is sent to ground via a daisy-chained lead to the self test switch.

3.5 Attract Mode Test Points

3.5.1 MPU Test Point Values

Model	TP1	TP2	TP3	TP4	TP5
AS-2518-17	+5 +/-.25VDC	+11.9 +/- 1.40VDC	+21.5 +/- 2.7VDC	GND	+5 +/-.25VDC
AS-2518-35	+5 +/-.25VDC	+11.9 +/- 1.40VDC	+21.5 +/- 2.7VDC	GND	+5 +/-.25VDC
AS-2518-133	+5 +/-.25VDC	+11.9 +/- 1.40VDC		GND	+5 +/-.25VDC

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.5.2 Rectifier Board Test Point Values

Model	TP1	TP2	TP3	TP4	TP5
AS-2518-18	+5.4 +/-.8VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC	7.3 +/-.9VAC	+43 +/-5.4VDC
AS-2518-49	+5.4 +/-.8VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC	7.3 +/-.9VAC	+43 +/-5.4VDC
AS-2518-54
AS-2518-132

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.5.3 Lamp Driver Test Point Values

Model	Board Type	TP1	TP2	TP3	TP4	TP5
AS-2518-14	Lamp Driver	+5 +/-.25VDC	GND
AS-2518-23	Lamp Driver	+5 +/-.25VDC	GND
AS-2518-43	Aux Lamp Driver	+5 +/-.25VDC	GND
AS-2518-52	Aux Lamp Driver	+5 +/-.25VDC	GND

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.5.4 Solenoid Driver/Regulator Test Point Values

Model	Board Type	TP1	TP2	TP3	TP4	TP5
AS-2518-16	Solenoid Driver	+5 +/-.25VDC	+190 +/-5VDC	+5 +/-.25VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC
AS-2518-22	Solenoid Driver	+5 +/-.25VDC	+190 +/-5VDC	+5 +/-.25VDC	+230 +/-27.4VDC	+11.9 +/- 1.40VDC
AS-2518-107	Combo Lamp/Solenoid Driver

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.5.5 Sound Test Point Values

Model	Board Type	TP1	TP2	TP3	TP4	TP5	TP6	TP7	TP8	TP9	TP10	TP11	TP12	TP13
AS-2518-32	Sound	+5 +/-.25VDC	GND	+12.5 +/-1.3VDC	+43 +/-5.4VDC	SOL RET	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-50	Sound	+5 +/-.25VDC	GND	+12.5 +/-1.3VDC	+43 +/-5.4VDC	SOL RET	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-51	Sound	+11.9 +/- 2.5VDC	+5 +/-.25VDC		0VDC (No Sound), 2.5+/-.2VDC (Sound)	+2.5 +/-.2VDC	0VAC (No Sound), .35 +/-.1VAC (Sound)	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-56	Sound	+11.9 +/- 2.5VDC	+5 +/-.25VDC	GND	0VDC (No Sound), 2.5VDC (Sound)	+2.5 +/-.2VDC	0VAC (No Sound), .35 +/-.1VAC (Sound)	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-57	Vocalizer	GND	+5 +/-.25VDC	Analog Output	Digital Input	Speech Clock	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
AS-2518-61	Sound	GND	+5 +/-.25VDC	+11.5VDC	-5VDC	Speech Volume Control Voltage	Sound Volume Control Voltage	AY3-8912 Output	E	TMS5200 Output	VMA	TMS5200 Clock	Reset
AS-2518-81	Reverb	GND			Audio In							+11.9VDC	+12VDC	+4VDC to +8VDC
M-051-00114-B045	Sound

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.5.6 Display Module Test Point Values

Model	Board Type	TP1	TP2	TP3
AS-2518-15	Display Module	+5 +/-.25VDC	+190 +/-5VDC	GND
AS-2518-21	Display Module	+5 +/-.25VDC	+190 +/-5VDC	GND
AS-2518-58	Display Module	+5 +/-.25VDC	+190 +/-5VDC	GND
AS-2518-121	Vidiot

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

3.6 Fuse Values

Model	Board Type	F1	F2	F3	F4	F5	F6
AS-2518-18	Power Supply	10A, 32V 3AG	3/4A, 250V 3AG SB	4A, 32V 3AG	5A, 32V 3AG	20A, 32V 3AG	3A, 32V 3AG SB
AS-2518-22	Solenoid Driver	1/4A, 250V 8AG	N/A	N/A	N/A	N/A	N/A
AS-2518-49	Power Supply	20A, 32V 3AG	3/4A, 250V 3AG SB	4A, 32V 3AG	5A, 32V 3AG	20A, 32V 3AG	N/A
AS-2518-54	Power Supply	20A, 32V 3AG	3/4A, 250V 3AG SB	4A, 32V 3AG	5A, 32V 3AG	20A, 32V 3AG	N/A
AS-2518-107	Combo Lamp/Solenoid Driver
AS-2518-132	Power Supply

Source: Bally Electronic Pinball Games Repair Procedures, F.O. 560-3

Unless noted otherwise, all fuses are fast blow.

Various Bally and Stern games have under playfield fuses as well. A common symptom of a blown playfield fuse is flippers operational, but no other on playfield solenoids work. This is because the flippers draw too much current for the under playfield fuse (which is usually 1 or 2 amp) so they are connected before the fuse is in the circuit. The main solenoid fuse on the rectifier board is used to protect against a shorted flipper coil instead.

Sometimes a large under playfield mechanism will be fused separately. Gottlieb did this often, but it is rarer in Bally/Stern games. If you have a solenoid not working it doesn't hurt to check and see if it has a fuse, or if someone decided to add one in the past. The under playfield solenoid fuse is a very small value as for the most part Bally/Stern games are only able to fire one solenoid at a time. This is a limitation of the hardware design, as the 4-to-16 decoder chip on the solenoid driver board can only decode one of 15 signals to fire an associated solenoid.

Some games do utilize the remaining 4 continuous drivers for a momentary coil. (One example is the ball walker area in Flight 2000 - the 2 kickers are activated by the continuous solenoids, for a momentary period). You should identify which under playfield solenoids if any are used as such in your game and add a fuse to the activation (single, thinner wire) side of the coil to prevent a software glitch from locking on that coil. Simply splice it inline with the single wire and use a 1 amp fast blow fuse to protect the driver circuit and coil in the case of a lockup. It would only be necessary to add the fuse for large loaded coils - relay or high resistance coils like on a flag gate or pop-up post coil relay do not place such a great load on the driving transistor that it is in any danger of burning out.

Weak playfield solenoids can be caused by a weak connection on the under playfield fuse holder. Remove the fuse and check for proper tension on the fuse clips for any tarnishing. It is best to just replace suspect fuse holders with new vs. attempting to clean the originals.

3.7 Jumper/ROM Info

Jumpers are small zero ohm resistors or pieces of bare or insulated wire used to connect various points of an MPU board together to allow the board to utilize varying sizes and types of ROM/EPROM chips. Many of the logic gate chips on the MPU boards are used to steer address signals to the proper pins on the various U1-U6 chip sockets. If you have changed the jumpers and you cannot make the board boot with known good working roms, it is possible you have an addressing problem caused by one of the logic gate support chips. Always double check your jumper work by following the trace or schematic to the next point after the jumper; i.e. do not just measure continuity across the jumper. Go to the next point where the jumper connects and test between those points.

Be careful soldering to the pads, as they can be fragile. It is best to remove all the solder from the pad and insert the jumper fully into the via rather than just solder to the top. Soldering the jumper top and bottom will help with any cracked vias. Solder the jumpers to the top of the board where the jumper silk screening is printed rather than the back so that you can easily spot what type of rom chips the board is jumpered for.

All software for Bally/Stern boards can be reformatted into a 2x2732 configuration. It helps to understand how the original software is formatted to understand how to combine and pad the software to get different formats. Any board jumpered to take 2x2732 has its address ranges of U2 as $1000-$17FF (lower half) $5000-$57FF (upper half). The U6 ranges are $1800-$1FFF (lower half) and $5800-$5FFF (upper half).

If the game was originally 4x2716, U1=$1000-$17FF, U2=$5000-$57FF, U5=$1800-$1FFF, and U6=$5800-$5FFF. Thus, to combine this setup to work on a 2x2732 configuration, you would combine U1+U2 into U2.732 and U5+U6 into U6.732 using either your burner software, or the DOS command copy /b u1.716 + u2.716 u2.732.

If you need to use 2716 eproms but don't have any, you can use a 2732 eprom in its place by duplicating the data. Either use the DOS command copy /b rom.716 + rom.716 rom.732 or load the data twice into your burner; depending on its software, you might change the buffer address by $800 (so the duplicate data loads after the first segment) or it might ask if you want to append the data to the existing buffer.

3.7.1 Bally AS-2518-35 or -133 Jumper Info

The following is a list or various ROM and EPROM combinations that can be used with the Bally -35 or -133 board and the associated jumpers and jumper cuts. The letter "E" has been eliminated on every jumper number after the first to save space. 9332 ROMS are the "Black" masked ROMS originally supplied by the factory and can be replaced with 2532 EPROMS without any modification to the original board, provided that board has not been altered.

U1 ROM	U2 ROM	U6 ROM	MPU Jumpers in Numeric Order	Jumper CUTS
9316	9316	9316	E1-4,2-6,7-8,9-11,12-36,13-15,16a-19,31-32,33-34
2716	74S474	74S474	E1-3,2-6,9-11,12-36,13-15,16a-18,31-32,33-35
	2532 or 9332	2532 or 9332	E4-12, 7-8, 10-11, 13a-14, 16a-34, 29-33, 31-32	E13-15
	2532 or 9332	2732	E4-12,7-8,10-11,13a-14,16a-29,31-32,33-35	E13-15
	9316	9316	E2-6,7-8,9-11,12-36,13-15,16a-19,31-32,33-34
9316	9316	2716	E1-4,2-6,7-8,9-11,12-36,13a-19,16a-18,31-32,33-35	E13-15
	2716	9316	E1-5,2-4,7-8,10-12,11-29,13a-14,16a-19,31-32,33-34	E13-15
	2716	2716	E1-5,2-4,7-8,10-12,11-29,13a-14,16a-18,31-32,33-35	E13-15
2716	2716	2716	E1-5,2-4,7-8,10-12,11-25,13a-14,16a-18,31-32,33-35	E13-15
2716	2716	9316	E1-5,2-4,7-8,10-12,11-25,13a-14,16a-19,31-32,33-34	E13-15
2716	2716	2532 or 9332	E1-5,2-4,7-8,10-12,11-25,13a-14,16a-34,29-33,31-32	E13-15
	2732	2716	E4-13a, 7-8, 10-11, 12-GND, 16a-18, 31-32, 33-35	E13-15
	2732	2732	E4-13a, 7-8, 10-11, 12-GND, 16a-29, 31-32, 33-35	E13-15
U1 ROM	U2 ROM	U6 ROM	MPU Jumpers in Numeric Order	Jumper CUTS

The -133 board was used in 3 games: Baby Pacman, Granny and the Gators, and Grand Slam. If you want to use a -133 board in a game that uses another board, you must change CR52 (a 1n4148 diode near J4) to a 2k resistor. If you want to use a -35 board in a game that requires a -133, change resistor R113 to a 1n4148 diode, banded end farthest away from J4. IMPORTANT: Before plugging the board in, measure the voltage at the MPU J4-15. If it is 6.3 VAC, this game requires a -133. If it is 43 VDC, the game requires the -35 configuration.

3.7.2 Bally AS-2518-17 and Stern MPU-100 Jumper Info

The following is a list of various ROM and EPROM combinations that can be used with the Bally -17 or STERN MPU-100 board and the associated jumpers and jumper cuts. The letter "E" has been eliminated on every jumper number after the first to save space. '9316 ROMS are the "Black" masked ROMS originally supplied by the factory. The "-DASH" between numbers means to jump one point to the other, e.g. E 1-2 means jump E1 to E2. Some jumps are very close to each other, others are much farther away. Some cuts in the traces must also be made on the solder or component side of the MPU board, so read the NOTES section below carefully.

U1 ROM	U2 ROM	U6 ROM	MPU Jumpers in Numeric Order	Jumper CUTS
	9316	9316	E1-2, 3-4, 6-7, 8-10	Usual Factory Setting
	2716	9316	E1-2, 3-4, 6-7, 8-10	Cut & Jumper See Note A
	2716	2716	E1-2, 3-4, 6-7, 8-10	Cut & Jumper See Note B
	2732	NONE	E6-7, 8-10	Cut & Jumper See Note C
	2732	2732	E1-2, 3-5, 6-7, 8-10	Cut & Jumper See Note D
74S474	74S474	2716 or 9316	1-2, 3-4, 8-9 Factory Setting for Freedom or Night Rider ONLY
2716		2716	See Note E	Freedom/Night Rider ONLY
U1 ROM	U2 ROM	U6 ROM	MPU Jumpers in Numeric Order	Jumper CUTS

3.7.2.1 Notes to above Cut and Jumper Section

If a jumper combination is NOT listed in the chart above, this jumper must be cut or removed! Double check your work and verify that someone else has not modified the board before you begin the process. Incorrect jumper combinations will prevent the MPU from booting, showing a locked on MPU LED. This is a very common fault.

Note A, 2716 in U2, 9316 in U6
In addition to the jumpers listed above, you must also make the following cuts and jumps to use this configuration.

1. On the component side of the -17 or MPU-100 board, cut the trace that runs from U2 pin 18 to U3 pin 18. Do this where the trace passes between sockets U2 and U3.
2. On the solder side of the -17 board, run a jumper from U2 pin 18, to U17 pin 11.
   
3. On the solder side of the -17 board, cut the trace going to U2 pin 21.
   
4. On the solder side of the -17 board, run a jumper from U2 pin 21 to U2 pin 24.
   

Note B, 2716 in U2, 2716 in U6
In addition to the jumpers listed above, you must also make the following cuts and jumps to use this configuration.

Make sure jumpers E1-2, E3-4, E6-7, and E8-10 are in place.

1. On the solder side of the -17 board, cut the trace leading to U18 pin 4.
2. On the solder side of the -17 board, connect U18 pin 5 to the trace you cut leading to U18 pin 4. It's easiest to run the wire from U18 pin 5 to the via ("trace thru dot") that connects to this trace.
   
3. On the solder side of the board, cut the trace leading to U2 pin 21.
   
4. On the solder side of the board, cut the trace leading to U6 pin 21.
   
5. On the solder side of the board, jumper from U2 pin 21 to U2 pin 24.
   
6. On the solder side of the board, jumper from U6 pin 21 to U6 pin 24.
   

Note C, Single 2732 at U2 for the early 1977 to 1979 games.
This modification combines the two original 9316 ROMs at U2 and U6 into a single 2732 EPROM at location U2. This configuration works for the following games only.

• Black Jack
• Bobby Orr Power Play
• Eight Ball
• Evel Knievel
• Mata Hari
• Night Rider

To combine the original 9316 (or 2716) U2 and U6 ROM images into a single 2732 U2 image, use this DOS command:

COPY /B U2ROM.716 + U6ROM.716 U2COMBO.732

Make sure to use the "/b" switch when copying, as shown above. The command combines the two files into a single binary file.

Add the following cuts and jumpers to the -17 MPU to use this configuration.

Reference the left picture.

1. Verify that jumpers E6-E7 and E8-E10 are in place. Remove any jumpers at E1, E2, E3, E4, or E5. That is, remove all jumpers except E6-E7 and E8-E10.

Reference the center picture.

2. On the solder side of the -17 board, find U18 pin 4. Cut the trace close to pin 4 as shown below. In the picture below, a blue/black dot marks the cut made with a Dremel "ball cutter" bit.
3. Scrape the solder mask from the trace leading to pin 4.
4. Tack solder one end of a short length of wire (or resistor lead) to the bare trace. Solder the other end to U18 pin 5. This connects U18 pin 5 to U2 pin 18. You may choose an alternate method. Just be sure to connect the trace from the "trace through hole dot" to U18 pin 5.

Reference the right picture.

5. On the component side of the board, locate U2 pin 13 (top right hand corner of U2). Slightly higher and to the right is a via "trace through hole" with a trace running straight down. Cut this trace to separate the via from the trace. In the picture below, the blue/black dot marks the location to cut.
6. On the component side, jumper from the via noted in step 5 to pad E4 (red wire in picture below). This connects jumper pad E4 to U2 pin 21.
7. On the component side, notice the large GROUND trace that runs down the board just to the right of the ROM sockets. To the right of the U2 ROM socket, scrape the solder mask from this large ground trace and add a jumper wire from this trace to pad E3 (orange wire/white tracer in picture below. Note that in this instance, U3 was also removed and the ground pad of U3 is used as a jumper point). This connects U2 pin 20 to ground.
8. Use your multimeter to verify that continuity exists between jumpered points.

• Note C Cuts and Jumpers
• 

  Component Side Jumper Locations
• 

  Solder Side Trace Reroute at U18 and "through hole" to U2, pin 18
• 

  Component Side Cut (black dot) and Jumper Detail

Note D, 2732 in both U2 & U6
This is a popular modification to the -17 & MPU-100 board as it maximizes the ROM space available and can accommodate almost every game from this period.

In addition to the jumpers listed above,make the following cuts and jumps to use this configuration. Make sure jumpers E1-2, E3-5, E6-7, and E8-10 are in place, & NO others are connected. It is a good idea to continuity check each of the necessary jumpers, BEFORE beginning work.

1. On the solder side of the -17 or MPU-100 board, cut the trace that runs to U2 pin 21.
   
2. On the component side of the board, cut the trace that runs to U2 pin 18. Best place to do this is where the trace passes between sockets U2 and U3. Use a mulitmeter continuity setting to figure out the trace to cut, and mark it with a Sharpie to avoid confusion and cutting of the wrong trace.
   
3. On the solder side, jump a wire from U2 pin 18 to U2 pin 12.
   
4. On the solder side, jump a wire from U2 pin 21 to U9 (6800CPU) pin 24.
   
5. On the solder side of the board, cut the trace that runs to U6 pin 21.
   
6. On the component side of the board, cut the trace that runs to U6 pin 18. A good place to do this is where the trace passes between sockets U6 and U5. Use your DMM's continuity setting to figure out the trace to cut.
   
7. On the solder side, add a jumper from U6 pin 18 to U6 pin 12. On the solder side, jump a wire from U6 pin 21 to U2 pin 21 (this connects both U2 and U6 pins 21 to U9 pin 24).
   
8. On the solder side, cut the trace that runs to U17 pin 2.
   
9. On the solder side, cut the trace that runs to U18 pin 4.
   
10. On the solder side, add a jumper from U17 pin 2 to U18 pin 4.

Note E Bally Freedom and Night Rider ONLY
These notes are for the Bally Freedom and Night Rider ROMs

These two games used an unique set of ROMs at U1 and U2. These are 74S474 or 7461 (512 byte) ROMs at U1 and U2, and a 9316 or 2716 (2K byte) at U6. According to Williams tech, they state that a U1 2716 EPROM and a U6 2716 EPROM can be used for these two games.If using a -17 or M-100 MPU with a U1 2716 EPROM and U6 2716 EPROM, there are some cuts and jumps required:

1. Cut the trace from U1 pin 18 to U2 pin 18.
   
2. Cut the trace from U1 pin 21 to pad E7.
   
3. On the solder side, add a jumper from U1 pin 21 to U1 pin 24.
   
4. On the solder side, add a jumper from U1 pin 18 to U17 pin 11.
   
5. On the solder side, add a jumper from U1 pin 22 to U2 pin 22.
   

3.7.3 Stern MPU-200 Jumper Info

The following is a list or various ROM and EPROM combinations that can be used with the Stern MPU-200 board and the associated jumpers and jumper cuts. 9316 ROMS are the "Black" masked ROMS originally supplied by the factory, used on the first few MPU-200 games. Stern switched almost exclusively to a 4x2716 configuration sometime around Seawitch through the end of their run and various boards have been spotted in the wild that seem factory with 2x2732 configuration. Galaxy has been spotted with an oddball 3x9316 + 1x2716 configuration.

U1 ROM	U2 ROM	U5 ROM	U6 ROM	MPU Jumpers in Numeric Order	Jumper CUTS
(empty)	2716	(empty)	2716	2-3, 5-7, 13-14, 16-18, 23-25, 32-33, 34-35	All others
9316	9316	9316	9316	1-5, 2-6, 8-9, 12-13, 16-18, 19-20, 22-25, 26-28, 29-31, 32-33, 34-35	All others
9316	9316	9316	2716	1-5, 2-6, 8-9, 13-14, 16-18, 19-20, 23-25, 26-28, 29-31, 32-33	All others
2716	2716	2716	2716	2-3, 5-7, 9-10, 13-14, 16-18, 19-21, 23-25, 27-28, 29-30, 32-33, 34-35	All others
(empty)	2732	(empty)	2732	1-2, 4-5, 13-15, 16-18, 24-25, 32-33, 34-35	All others
U1 ROM	U2 ROM	U5 ROM	U6 ROM	MPU Jumpers in Numeric Order	Jumper CUTS

To combine the 9316 or 2716 ROM images into the proper format 2732 images, use the following MSDOS commands.

• copy /b U1ROM.716 + U2ROM.716 U2Combined.732
• copy /b U5ROM.716 + U6ROM.716 U6Combined.732

Note that jumpers 32-33 and 34-35 control the clock speed of the MPU-200. To use an MPU-200 in a game that normally uses a Bally -17/-35 or a Stern MPU-100 board, you should remove these jumpers as they will cause the software to run faster. This isn't really a problem, but timings of sound events might be affected as well as other unforeseen consequences. If using a MPU-200 board in a Bally -17 or -35 or a Stern MPU-100 game, you can remove the 5101 RAM at U13, as it will not be accessed. If the chip or socket at U13 is bad, it can be ignored. This however is a waste of resources, as the MPU-200 board is hard to find and cannot be substituted by a -17 or -35 board without some modifications.

Additionally, if all 32 dip switches are turned off upon boot with an MPU-200, it will flash seven times and jump into self-test mode. This will toggle alternatively every solenoid, flashing controlled lamps, and test each digit on the score displays. At least one DIP switch must be on to avoid this. This is not a function of the board itself, just the software used. For example, if you put earlier stern software (previous to Meteor) or any Bally software in an MPU-200, it will not enter self-test with all dips off.

• To down-grade the MPU-200 to the older MPU-100, remove jumpers 32-33 and 34-35 (used on all Stern MPU-200 EPROM configurations), and remove the 5101 RAM chip from U13.

• The MPU-200, when jumpered for four 2716 EPROMS (U1,U2,U5,U6), will run Bally games using three 2716 (U1,U2,U6) ERPOMs.

• On a MPU-200 configured for four 2716 EPROMs (U1,U2,U5,U6), to run Bally games using two 2716 (U2,U6) EPROMs, change the MPU-200's jumpers E13-14 to E13-15, and E5-7 to E1-5.

3.8 Bally / Stern MPU Board LED Never Lights or is Locked On

If the LED never lights, either the +12v (TP2, J4 pin 12) is missing or the LED is bad. By default, the LED is ON until the software tells U11 to turn it OFF.

If the LED lights solid, there's some digging to do. First off, if the board has any corrosion damage at all, it needs to be cleaned and neutralized before attempting any repairs. While shot-gunning components might fix the board, it won't be 100% reliable if the corrosion isn't addressed.

Make sure you are getting a solid power path from the rectifier board through the solenoid driver / power regulator board to the MPU board. A locked on LED can be caused by a poor connection anywhere in this chain. Sometimes reseating connector J4 on the MPU board (lower left) will 'clean' a connector well enough to make a better connection. While this may be a short term fix, be aware that any connector, which seems to work better after being reseated, really should be repinned and have its header pins replaced.

Next, put your DMM or a logic probe on pin 40 of the 6800 cpu chip (U9). Power on the board. You should see the voltage remain low / at zero, and then approx 1/10 of a second later, rise to about +5 vdc (high). This is the reset signal, which originates from the components in the lower left corner of the board, and is sent throughout the board to U9, U10, and U11. What the reset section (called the 'valid power detector') does is not allow the MPU to boot until the +12 volts are stable over the value of ZR1 (a zener diode, usually either 8.2 or 9.1 volts). This delay ensures that the +5 voltage is stable enough to run the MPU board reliably (the +5 volts is derived from the +12 volts on the solenoid driver / power regulator board).

The 6800 CPU chip will not 'unlock' and start program execution until it sees a transition from a low (0 volts) to high (~5 volts) signal. This is the purpose of the power on reset delay. The reset delay and signal must be present at all three of the reset inputs at U9 (pin 40), U10 (pin 34), and U11 (pin 34). If the signal starts out immediately at a high level, the MPU will not start to boot until the transition takes place. If you have a locked on MPU, you can take a screwdriver or your meter probe and short pins 39 and 40 together for a brief moment on U9. If the game starts to boot after doing this, it's a safe assumption that the reset circuit is to blame. Shorting the pins together simulates what the reset circuit does.

If you need to rebuild the reset circuit, full kits are available from specialty suppliers such as Great Plains Electronics or Big Daddy Enterprises. The kits include all replacement components in the corrosion zone. Bare bones, component replacements are Q1 (2n3904 or 2n4401) and Q5 (2n4403 or 2n3906), but it is a good idea to go ahead and replace all the parts that come in the kit. Replace components one at a time to ensure that you do not mix any up. Note there are a some components that are polarized in their installation, which include VR1, CR5, Q1, and Q5. Look carefully at the board to see if there are traces on the top and bottom of a component. The continuity at a through hole can be compromised due to alkaline corrosion. Therefore, it is recommended to solder these components from the top and bottom of the board to ensure that a good connection is maintained.

The following is the list of parts for the reset section that should be replaced. Parts listed with more than one type are equivalent and can be substituted freely. It is also possible that the inductors L1 and L2 need to be replaced as well, however this is very rare. If there is heavy corrosion on them they should be replaced.

Transistors:

Q1 - 2N3904/2N4401 (lower left area)

Q2 - 2N3904/2N4401 (near LED)

Q5 - 2N3906/2N4403 (lower left area)

Diodes:

VR1 - zener 1N9598/1N4738A

CR44 - 1N4004 rectifier diode

CR5, CR7 - 1N4148 switching diode

CR8 - LED

Capacitors:

C1, C2 - 820pF ceramic capacitor

C3 - 0.01uF ceramic capacitor

C5 - 4.7uF tantalum capacitor

C13, C80 - 0.01uF ceramic capacitor

Resistors: (1/4 w unless noted)

R1, R3, R24, R28 - 8.2k

R2 - 120k

R11 - 82 ohm/2 watt

R12 - 270 ohm

R16 - 2k

R16 - 2.2k (stern mpu-200 only)

R17 - 150k

R29 - 470 ohm

R107 - 3.3k

R112 - 1k

R134 - 4.7k

R140 - 20k

If your reset circuit is operating as designed, yet the LED is still locked on, next step is to pull all the chips from the board except for U9, U11, and U6 (leave all chips U1-U6 installed on Stern MPU boards. Only U6 is required on Bally boards to perform the initial LED turn off). It helps to have a known working U6 from a Bally game to use as a test chip for this purpose. Be aware that you need to know/have the board jumpered for the correct type of chip you're inserting.

See if the board starts and turns off the LED with just the chips above installed - if it does, add these chips back in this order to see which might be bad: U10 PIA, U1-U5 program chips, U7 6810 ram, U8 5101 ram. Often a bad ram/rom can cause the entire system to lock up. Bad chip sockets can be a factor as well; the early Bally -17 boards have a closed type brown socket that's especially prone to failure.

Double check the jumpers to ensure they match the ROM chips you have available, and change the ROM chips to known working ones for testing. A final thing to check if the machine won't boot is the clock circuit. It is fairly robust, and far more common that the reset circuit itself or chip sockets are the issue. To check the clock circuit you need a logic probe or oscilloscope. A multimeter might show the average voltage on a clock circuit, or it might just show meaningless constantly changing numbers. The clock signal is pin 3 on the CPU chip, and the shifted clock signal goes to pins 36 and 37. The frequency is about 500 kilohertz for Bally -17, -35 and Stern MPU-100 boards, and approximately 850 kilohertz for the Stern MPU-200 board.

If the clock signal is missing, pull U9 first to make sure the CPU chip isn't damaged, and test it again.

It can be frustrating to track down a locked on LED problem, but breaking the problem up and testing each section individually helps. Just remember that if the LED turns on and then off, most of the battle is won. The board has booted far enough that the software was able to start and turn off the LED. Proceed onto the LED flash testing to determine what needs to be fixed beyond that.

3.9 Bally / Stern MPU Board LED Flash Sequence

Upon start up, Bally and Stern boards have an LED that flashes. The LED is used to convey the results of specific tests conducted on various parts of the system. This section explains what is being tested and how, according to information from the Bally "FO-561-2 Theory of Operation rev. 5-1982" manual, and the Stern manual "Theory of Operation, Stern's Microprocessor Controlled Solid-State Games".

When power is first applied to the MPU board, the LED by default is ON. The very first set of valid instructions in every Bally / Stern game is to turn the LED off. This is more of a flicker than a flash, so is not counted as a flash in the 7 flash sequence.

3.9.1 Quick summary

Flicker: MPU reset good, program booted.
1st Flash: ROM Checksums OK
2nd Flash: U7 6810 ram OK
3rd Flash: U8 5101 ram OK (U8 & U13 on mpu-200)
4th Flash: U10 PIA OK (see details for caveats)
5th Flash: U11 PIA OK (see details for caveats)
6th Flash: U12 555 Display interrupt timer OK
7th Flash: Zero crossing interrupt detector OK (solenoid voltage present)

3.9.2 LED flicker:

The LED flicker tells you the CPU chip was able to start a valid program stored in the EPROMs, and that the reset circuit itself is good.

3.9.3 First flash:

After the program is running, it performs a checksum of all programmed chips U1-U6. Most Bally games' programming is split between an operating system chip U6 and a game ROM chip at U2. Stern games were a little looser. The operating system and game code are freely interspersed.

Bally checksums are calculated by summing each byte, and discarding any carries. Most games check their code in $0400 blocks, so it would be possible to determine down to the chip which chip failed this checksum. (A 2716/9316 chip has hex $0800 space available in it - 2732 sized images are $1000 in size. The smallest chip used was a 474 PROM which has $0200 bytes available) However, to do so would require a way to read the X register from the 6800 CPU chip at the time of checksum failure. So if you do not get the first flash, it is best to replace the U6 chip first, then move onto the other chips - U5, U2, and U1 (if present).

Stern checksums are calculated similarly, but not in chunks. The entire program space is summed and must equal $00 for the first flash to occur.

Regardless of whether the manufacturer is Bally or Stern, after the checksum is passed, the first flash occurs.

3.9.4 Second flash:

Next, the program tests the 6810 RAM chip at U7, by writing the data $00 to each memory location contained in the RAM ($00-$7F). It then reads back each location to ensure that $00 is returned. It increments the data to $01 and repeats this test. This continues until the data read back is $FF (256), which is the maximum value of any one byte stored in the RAM. It then increments the memory location being tested, and repeats the $00-$FF data storage test. If any of the tested locations return an unexpected result, the program stops, and alerts you to a problem with U7 (since you got the first ROM checksum flash, but not the 2nd U7 OK flash).

3.9.5 Third flash:

Now, the program tests the non-volatile 5101 RAM chip at U8 (U8 AND U13 on Stern MPU-200 boards). The 5101(s) store(s) bookkeeping data, game parameters, high scores, replay levels, etc. The program tests this RAM ($200-$2FF) by reading the original nibble / byte (see sidebar), and saves it in a temporary location. Then, it stores a test pattern in the location similar to the U7 test. After the byte successfully passes the test, the original data is returned to the location, and the program loops onto the next byte.

LEARN MORE: How does a 128 byte 5101 RAM occupy 256 memory locations?

If you look at a pinout of the 5101 memory, you will notice it is a 128 byte device. Yet, it is addressed by the MPU via 256 memory locations ($200-$2FF). This is because the 5101 is actually a 256 nibble device - a nibble is a half-byte (4 bits). So data stored to a 5101 in a pinball machine actually only stores half of the data byte being sent to it. Which half it stores is dependent on the board design. Bally and Stern use the upper nibble for storage, and Williams used the lower nibble. Stern MPU-200 boards have an additional 5101 at U13. This stores the lower nibble in conjunction with U8 storing the upper nibble of a byte saved to $200-$2FF. This allows MPU-200 games to store more data, and avoid doing some fancy processing by getting the data in and out of the non-volatile ram area.

For example, here's some pseudo-machine code for what happens:

• LOAD #$24 (the data you want to store is 24)
• STORE $231 (you want to store the data 24 at memory location $231)
• READ $231 (you want to read back the data you just stored)

The data returned is not #$24 as expected, but rather #$2F. The lower nibble was never stored, because the 5101 memory does not store data as bytes but rather as nibbles. To store #$24 properly would require splitting the byte into its nibbles '2' and '4'. The 2 would be stored in one memory location, while the 4 would be shifted, and stored in another memory location.

Showing the byte as binary might be helpful to visualize what's involved. The hex #$24 in binary is %00100100. Split into nibbles is %0010 (the 2) and %0100 (the 4). The upper nibble is the one the 5101 is able to store directly, but the position in the byte of the lower nibble prevents it from being stored. A shift operation is performed 4 times on the byte to reposition the lower nibble as the upper nibble, which enables it to be stored to the 5101. Each shift moves the binary pattern to the left one bit - here's the full sequence:

• Start=%00100100
• Shift left=%0100100x
• Shift left=%100100xx
• Shift left=%00100xxx
• Shift left=%0100xxxx

This gives the #$4 in the high nibble. All byte data has to be split this way to be saved, and recombined upon reading from boards (Bally -17 and -35, Stern MPU-100) with a single 5101 RAM chip. You can see why Stern added the second 5101 RAM to their boards. It makes programming much easier!

3.9.5.1 Continuity Chart for U8 5101 RAM in a Bally AS2518-17, -35 or Stern MPU-100 Board

IC & Pin#	Data Address	Continuity Points
U8 pin 1	(A3)	U7 pin 20, U6 pin 5, U9 pin 12
U8 pin 2	(A2)	U7 pin 21, U6 pin 6, U9 pin 11
U8 pin 3	(A1)	U7 pin 22, U6 pin 7, U9 pin 10, U11 pin 35
U8 pin 4	(A0)	U7 pin 23, U6 pin 8, U9 pin 9, U11 pin 36
U8 pin 5	(A5)	U7 pin 18, U6 pin 3, U9 pin 14
U8 pin 6	(A6)	U7 pin 17, U6 pin 2, U9 pin 15
U8 pin 7	(A7)	U7 pin 15, U6 pin 1, U9 pin 16, U11 pin 24
U8 pin 8		GROUND
U8 pins 9&10	(D10&D00)	U7 pin 6, U6 pin 14, U9 pin 29, U11 pin 29 (* pins 9 & 10 siamesed together)
U8 pins 11&12	(D11&D01)	U7 pin 7, U6 pin 15, U9 pin 28, U11 pin 28 (* pins 11 & 12 siamesed together)
U8 pins 13&14	(D12& D02)	U7 pin 8, U6 pin 16, U9 pin 27, U11 pin 27 (*pins 13 &14 siamesed together)
U8 pins 15&16	(D13&D03)	U7 pin 9, U6 pin 17, U9 pin 26, U11 pin 26 (* pins 15&16 siamesed together)
U8 pin 17	(CE2)	Q5 Right Upper leg, U9 pin 40, U11 pin 34
U8 pin 18	(OD)	U18 pin 6
U8 pin 19	(CE1)	U17 pin 8
U8 pin 20	(R/W)	U7 pin 16, U9 pin 34, U11 pin 21, U18 pin 7
U8 pin 21	(A4)	U7 pin 19, U6 pin 4, U11 pin 22
U8 pin 22	(Vcc)	C13 Left Leg, R12 upper Leg, CR5 Lower Leg

3.9.5.2 U8 & U13 5101 RAM Continuity Chart for Stern MPU-200 ONLY

IC & Pin#	Data Address	Continuity Points
U8 pin 1	(A3)	U13 pin 1, U7 pin 20, U6 pin 5, U9 pin 12
U8 pin 2	(A2)	U13 pin 2, U7 pin 21, U6 pin 6, U9 pin 11
U8 pin 3	(A1)	U13 pin 3, U7 pin 22, U6 pin 7, U9 pin 10, U11 pin 35
U8 pin 4	(A0)	U13 pin 4, U7 pin 23, U6 pin 8, U9 pin 9, U11 pin 36
U8 pin 5	(A5)	U13 pin 5, U7 pin 18, U6 pin 3, U9 pin 14
U8 pin 6	(A6)	U13 pin 6, U7 pin 17, U6 pin 2, U9 pin 15
U8 pin 7	(A7)	U13 pin 7, U7 pin 15, U6 pin 1, U9 pin 16, U11 pin 24
U8 pin 8		U13 pin 8, GROUND
U8 pins 9&10	(D10&D00)	U13 pins 9 & 10, U7 pin 6, U6 pin 14, U9 pin 29, U11 pin 29 (* pins 9 & 10, siamesed together)
U8 pins 11&12	(D11&D01)	U13 pins 11&12, U7 pin 7, U6 pin 15, U9 pin 28, U11 pin 28 (* pins 11 & 12 siamesed together)
U13 pins 11&12	(D11&D01)	U7 pin 3, U6 pin 10, U9 pin 32, U11 pin 32
U8 pins13&14	(D12&D02)	U13 pins 13 & 14, U7 pin 8, U6 pin 16, U9 pin 27, U11 pin 27 (*pins 13 &14 siamesed together)
U13 pins 13&14	(D12&D02)	U7 pin 4, U6 pin 11, U9 pin 31, U11 pin 31
U8 pin 15&16	(D13&D03)	U7 pin 9, U6 pin 17, U9 pin 26, U11 pin 26 (* pins 15&16 siamesed together)
U13 pins 15&16	(D13&D03)	U7 pin 5, U6 pin 13, U9 pin 30, U11 pin 30 (* pins 15&16 siamesed together)
U8 pin 17	(CE2)	U13 pin 17, Q5 Right Upper leg, U9 pin 40, U11 pin 34
U8 pin 18	(OD)	U13 pin 18, U14 pin 9
U8 pin 19	(CE1)	U13 pin 19, U17 pin 8,
U8 pin 20	(R/W)	U13 pin 20, U7 pin 16, U9 pin 34, U11 pin 21, U14 pin 10
U8 pin 21	(A4)	U13 pin 21, U7 pin 19, U6 pin 4, U11 pin 22
U8 pin 22	(Vcc)	U13 pin 22, C13 Left Leg, R12 upper Leg, CR5 Lower Leg

3.9.5.3 Issues with 5101 RAM chips

The socket at U8 or U13 is very close to the corrosion effects of the alkali of a leaking battery. This is often the cause of boards not showing a 3rd flash. There are traces on the component and solder side of the board, and the socket can hide corrosion to these traces. In turn, the corrosion can affect the 5101 chip's contact with the socket pins.

Unless the board is unusually clean, a rebuild of a non-working board should include replacing the socket at U8 (and U13, for MPU-200). The chip is an oddball configuration with 22 pins which makes machine pin sockets hard to find. Use 2 strips of machine sockets, so that you can solder both above and below the board. Inspect the traces closely on the top; it is best to avoid soldering on the top of a board unless you have to as it makes it extremely difficult to desolder the sockets in the future. Take extreme care not to make a solder bridge of the traces on the component side, as it is easy to do. Performing a continuity test to adjacent socket legs after soldering is a good practice. Also, note that some of the pins are shorted together. (see above)

Failure to achieve the third flash can also be attributed to the following: If the U8 and U13 (MPU-200) show correct continuity as charted above, and the 5101 RAM is known to be good, the problem could lie with the U19 (4011) chip. On Stern MPU-200, replace U14 (4572) instead. Finally, although rare, the 6800 CPU at U9 could be bad.

The speed of the 5101 RAM chip can make a difference in the functioning of an otherwise good MPU board. If a slow chip is put into a good MPU, strange behavior such as inconsistent boot ups, incorrect score display behavior, among other things can result from the RAM not being able to keep up with the demand from the CPU. Below is a list of 5101 RAM chips and their speed. A lower number means a faster chip. A Stern MPU-200 board needs 2 chips of at least 450ns, while the Bally AS 2518-17 or -35 and the Stern MPU-100 can work correctly with a slower chip of 650ns. The stern mpu-200 board should have matching speeds for the 2 rams as they are selected and accessed simultaneously. A faster chip is fine for a replacement, but there will not be a performance enhancement.

• PCD5101P (Philips manu) 150ns
• 5101-1 450ns
• 5101L-1 450ns
• 5101L-2 450ns
• 5101-2 450ns
• 5101 650ns
• 5101L 650ns
• 5101-3 650ns
• 5101L-3 650ns
• 5101-8 800ns (too slow for any board)

The 5101 RAM chip is especially sensitive to static discharge that will damage it, so take extra precaution in handling. The memory RAM replacement chip sold by Tom Callahan at pin-logic.com uses a 6116 and special adapter, and makes a good replacement. Pin-logic also sells the static ram chips that do not require batteries for backup; although he advertises that these do not work in the Stern MPU-200 board, 2 of them did work on a test board. Another source for varying types of 5101 and 6116 replacements is a blog site WarpZoneArcade. There is information how to roll-your-own 5101 replacement adapters. Or, visit its accompanying site, PinForge, and purchase pre-made RAM adapters.

3.9.6 Fourth and Fifth flashes:

Next, the program tests each of the 2 6820/6821 peripheral interface adapters (PIAs) at U10 and U11, starting with U10. The PIAs are set to a known state, then data is stored and read back from them to verify their registers are functioning properly. It is important to note that it is not possible for the PIA to be 100% tested with this test, as external data would have to be fed in to do so. However, the test will at least test the internal registers. It would be possible for a PIA to pass the self-test, but still not work properly with external inputs.

Assuming the PIAs pass, the fourth (U10) and fifth (U11) LED flashes occur. The LED itself is connected to the U11 PIA. So if the LED is locked on, U11 might be bad. It's worth letting a locked on LED board 'sit' for a minute or so to see if the game boots all the way up without flashing each test step. This is an example of how a PIA can pass self test but still be bad. The LED control pin has no feedback as to if the LED is in fact flashing.

3.9.7 Sixth flash:

The sixth flash waits for an external input on U11 pin 40 from the display interrupt generator circuit, which occurs 320 times a second. If you're missing the sixth flash, there may be a problem with either the U12 circuit, OR the input pin on the PIA. A logic probe, oscilloscope, or a multimeter on pin 40 can help you determine which is at fault. A logic probe will pulse if the display circuit is operating; the scope will show you the signal's waveform; and the multimeter should settle on a voltage somewhat between 0-5 volts.

One definite reason for lack of a sixth flash is a poor connection on the ground side of C16, the film capacitor. If there isn't a sixth flash, but all other tests and measurements are good, it's a safe bet that U11 is bad and needs to be replaced.

Note that the sixth flash does NOT check for the proper frequency of operation of the display generation circuitry. As long as there is a pulsing signal (technically, ONE state change), the test is marked good and the program allowed to continue.

3.9.8 Seventh flash:

The last flash waits for an external input on U10 pin 18 from the zero crossing detector circuit, which occurs 120 times a second (as the AC waveform passes or "crosses" 0 volts). Diagnosis of issues with the 7th flash are similar to the 6th flash. You can measure the input to pin 18 to determine if the signal is present or not. A signal present, but no flash could mean a bad U10 PIA. A missing signal usually points to missing solenoid voltage. The source of the zero crossing signal is derived from the solenoid voltage delivered from the rectifier board. Equally, if a signal is present, there may be an issue with the zero crossing detection circuit itself.

Note again that the seventh flash does NOT check for the proper frequency from the zero crossing detector. It simply checks for a pulsing signal, and only checks for ONE transition.

After the 7th flash, the program does some background setup: reads dip switches, enables the displays, attract modes, switch scanning etc. in a 'game over' mode, waiting for player input. The LED will sometimes be dimly glowing or even pulse as this happens, which is not a cause for alarm. You can rebuild the LED circuit around Q2 if this worries you, but it is harmless.

One interesting anomaly is that the 7th flash will not occur, if there is a bad 1N4004 diode (CR3) used on -32 / -50 sound boards. On these two sound boards, the +12VDC used on the boards is derived from the +43VDC solenoid voltage, and isolated by CR3.

3.10 The Single Largest Culprit in MPU death

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By far the largest reason the MPU board stops working is because of alkaline corrosion from the on-board rechargeable batteries. The original battery used on the board is a 3.6 volt nickel cadmium rechargeable battery; over time, this type of battery leaks corrosion into the traces surrounding it, affecting the 5101 memory, the reset circuit, the 6810 memory, the LED area, and all the traces around it. One of the worst boards had corrosion stretching throughout the entire ground plane of the board.

3.10.1 Get rid of that battery now!

If you have a battery on the board, it is recommended to remove it immediately. There are several different ways to replace the battery; in order of preference: 5101 ram eliminator, memory capacitor, nothing, lithium battery, remote mounted AA battery pack, exact replacement. Let's look at each of the options in turn and weigh their pros and cons.

5101 Ram Eliminator

A 5101 ram eliminator doesn't eliminate the ram per se; it replaces it with a more modern ram that is either flash ram or has an internal battery built into it.

Advantages: eliminating a static sensitive obsolete part, eliminating any type of battery that could leak, high reliability, very long retention time (10-99 years)

Disadvantages: relatively high cost, need to remove the 5101 (if not socketed) and replace or add a socket, stressing relatively frail mpu board traces, flash ram type can wear out (although unlikely)

Memory Capacitor

A small capacitor (5.5 volt 1.5 farad works well) is added to the board in place of the original battery. The charging circuit for the rechargeable battery works just fine in maintaining enough of a voltage to enable the capacitor to act in place of the battery.

Advantages: relatively low cost, easy installation, no risk of battery leakage, high reliability

Disadvantages: large initial charge time, some 5101s draw too much current, must turn machine on every couple of months to top off capacitor

Nothing

Removing the battery and cleaning the board up, you do have the option to replace the battery with nothing. If you don't care about audits, settings, or high scores, this is a valid option. Some software might not like having random garbage in its memory range, though. If you have a stern mpu-200 based game, do not leave the battery out as the random garbage will cause problems with stern's software.

Advantages: No risk of leakage, ever

Disadvantages: No high scores save, no audits, garbage in ram can cause issues with some software

Lithium Battery

Replacing the original nickel cadmium battery with a lithium battery is possible; however it is imperative that you add a blocking diode to prevent the battery from being charged.

Advantages: Very long life (10 years on average), cheap, can be mounted far from boards so any leakage would not leak onto boards

Disadvantages: Must use blocking diode, can leak (unlikely), any leakage difficult to clean up

Remote Mounted AA Battery Pack

A popular and inexpensive option is to replace the original battery with a small AA pack, with a blocking diode. Like the lithium replacement option, it is essential to have a blocking diode (usually incorporated into the pack) so the mpu doesn't try and charge the AA batteries. If you get lithium AA batteries you can get very long life. This type of battery pack needs to be checked periodically to ensure no leakage is occurring.

Advantages: Low cost, can be moved far from boards so if batteries so leak they do not leak directly onto boards

Disadvantages: Periodic maintenance (replacing/checking), can leak

Exact Replacement

You can replace the NiCad with a NiCad. Not recommended as all of the original pitfalls of the original battery are still present, but it will work. Many people use cordless phone batteries to do this; just make sure the voltage and amp hour rating are similar to the original battery. (3.6 volt 150 milliamp hours)

Advantages: Low cost, can also be mounted far from boards so any leakage does not leak directly onto boards

Disadvantages: Can leak, needs periodic maintenance (checking for corrosion)

Note that all of the replacement options that include batteries are subject to the same conditions causing leakage as the original battery was. It is strongly recommended that if you decide to use a solution that uses a battery as its power source to remotely mount the battery so that any future leakage does not drip onto the boards. The bottom of the head is a good choice as is the sidewall in cases where there are no boards mounted there. Corrosion can and does travel through the wiring used to relocate the batteries however, so periodic inspection of the batteries and board are necessary to ensure that no further corrosion is occurring.

3.10.2 Installation of Various Battery Eliminators

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AA Battery pack

4 AA cell battery holder & diode

One inexpensive option is to replace the Ni-Cad rechargeable battery pack with a 4 AA battery pack plus diode using ordinary alkaline batteries. You must install a blocking diode (1N5817 or 1N4004 work fine) to prevent the game from trying to charge the battery and causing damage. Install the diode in the 1st bay with the banded side soldered to the "+" or RED terminal and the non-banded end to the "-" BLACK negative spring. Having a battery backup will save high scores & credits, and some sound settings. The holder can be mounted in a convenient spot in the backbox, and leads soldered to the MPU and a Molex .062 2 terminal pin and socket connected to the battery holder for easy servicing of the MPU. Mouser P/N 12BH348-GR for the 4 AA pack.

Memory Capacitor

Remove original battery, neutralize and clean any corrosion left behind/inspect parts in area, replace as needed. Drill a small hole to the left of the original batteries' negative terminal. Install the capacitor with the negative lead in the leftmost hole of the negative terminal, soldering it into place. Solder a lead to the positive terminal of the capacitor and bend the leg over to help hold it in place. Solder the other end of the lead to either the positive hole from the original battery, or to the bottom lead of R12. Double check your work in reference to the negative lead of the capacitor. Turn the machine on an let the capacitor charge for between 8-12 hours. Once the cap is charged, turning the machine on for about an hour a month will keep it topped up.

Original style battery, cordless phone battery

Remove original battery, neutralize and clean any corrosion left behind/inspect parts in area, replace as needed. Solder new battery in, or better yet, attach fly leads to battery and remote mount. Turn machine on for large initial charge to battery.

3.11 Bally Solenoid Driver for Dummies

First off, take a look at the picture below:

This is a typical Bally coil from a Mata Hari machine. Notice 3 things: The two big fat yellow wires going to one lug, the small skinny wire going to the other lug, and the diode connected to the two lugs.

One lug on every coil is visited by these fat wires, in what's called a daisy-chain. This is the wire that supplies each coil with positive 43 volts DC (+43VDC). So each coil is connected to the +43VDC bus. Most have two fat wires, but some may have one. Flipper coils have these wires too, but they are connected a little differently, and are discussed elsewhere. For now, just assume we're talking about regular solenoids here.

Next, you'll notice each coil has a small skinny wire on the other lug. This wire goes to the control circuits on the solenoid/regulator board. In order to energize the coil, there must be a path to ground for the +43VDC. Normally, there is not so the coil is relaxed. When the small skinny wire gets connected to ground, the path is complete and current will flow. This current flow turns the coil into an electro-magnet and then pulls the plunger into the coil. When the wire is disconnected from ground, current flow stops, the electro-magnet is turned off, and the plunger returns to it's normal position, with help from either a spring, or gravity.

Finally, the diode. When the current is quickly turned off on an energized coil, the magnetic field around the coil collapses quickly and causes the coil to generate a huge voltage spike. The job of this diode is to prevent the majority of this spike from reaching the solenoid driver circuity. If the diode is bad, or installed backwards, you'll pop the driver transistor the first time the coil is energized, then released. It's like the ignition in older cars - when the points open, the 12 volts is removed from the car's coil quickly, which causes another coil to generate a huge voltage spike, to the spark plug. The computer program that runs the machine also tries to limit this spike by turning off the coil near the zero crossing of the line AC. This helps because the DC that drives the coils is rectified, but not filtered, so it's not smooth DC, but "humpy", like in this picture:

By energizing the coils just after the zero crossing, the in-rush of current caused by a coil is limited, and by turning them off just after the zero crossing, the voltage spike caused by the collapsing field is also kept to a minimum.

So, in the simplest form, the solenoid driver circuits in your Bally look like this:

Look at it as a bunch of coils all connected to the +43VDC bus, and the other lugs going to switches which are also connected to ground. Then, if you were to close a switch, that would connect the circuit from +43VDC to ground, and the coil would energize as long as the switch is closed.

Now see how the circuit is complete due to the switch being closed, and the coil is energized. Then you open the switch and the coil turns off and you're back to the first picture. If the diode were not there, when you opened the switch, there's be a big arc across the switch contacts at the moment they opened up.

Finally, take this one step further and replace the manual switches with transistors. Transistors are normally used as amplifiers, but you can also use them as switches too. There are 3 leads on a transistor, the base, the emitter, and the collector. For NPN transistors like the ones on your Bally solenoid driver, you can used the emitter and collector like a switch. With no current supplied to the base, there is no current flow between the collector and emitter, so the transistor switch is open, or OFF. If you supply a current to the base, current will then flow between the collector and emitter, so now the switch is closed, or ON.

Without getting into too much detail - what happens is a current is applied to the base which is high enough to 'saturate' the transistor. This means the collector-to-emitter current will be amplified as high as it can, and the transistor will then conduct a large amount of current from COLLECTOR to EMITTER, in relation to the current flow from the BASE to the EMITTER. This is how it acts like a switch. The base goes high to turn it on, and low to turn it off. Since the collector is connected to the wire that goes to the coil (the small single wire), and the emitter is connected to ground, turning the transistor as the effect of connecting the collector to ground. This completes the circuit to the coil and it fires.

You may have heard that you can test a coil by grounding the tab on the coil's driver transistor. For the TIP-102 transistors used in the Bally solenoid driver, the metal tab is connected to the collector. Knowing this, and what you've just learned, you can now see that grounding the tab is the same as grounding the collector, which will complete the circuit to ground and fire the coil. Note that this test only tests the wiring from the solenoid driver to the coil. It DOES NOT test the transistor, or any circuitry before the transistor.

So, you can now replace the transistor and "control signal" in the simplified drawing above, with the actual circuit and more details found in the following section.

3.12 Bally Solenoid Driver

Bally AS-2518-16 Solenoid Driver/Regulator

Bally AS-2518-22 Solenoid Driver/Regulator

Stern SDU-100 Solenoid Driver/Regulator

Another style of the Stern SDU-100 Solenoid Driver/Regulator

First off, everything mentioned on this page is in reference to the Bally AS-2518-22 model solenoid driver board, found in most Bally pins from 1977 through 1985. Since it is very similar to the AS-2518-16 board and is identical as far as the operation of the solenoid driver circuits, you can assume it is applicable for these boards as well.

Second, if all this is Greek to you and you have no idea how Decoder ICs work, or what a Transistor is, take a look at the Bally Solenoid Driver for Dummies article above first to learn the basics of how this stuff works.

Thirdly, this model of solenoid driver board actually has three functions: The first obviously is to drive the solenoid and relay coils of your pin, the second is a 5-volt regulator which provides a nice and steady 5 VDC to the other boards for their various logic circuits, and third is the high voltage regulator (190 VDC) for the display driver boards. I won't be discussing the voltage regulator stuff here, just the solenoid driver parts.

Finally, Don't forget that the Solenoid Driver board contains the high voltage circuitry for the displays. There is 190 volts DC here and if you're not careful, you'll get knocked on your ass. A shock from 190 volts DC will hurt. If you don't know what you're doing, then keep away from it and have a professional fix it instead. In addition to high voltages, there are static sensitive parts on this board, so if you're going to work on it, be sure to properly ground yourself before touching the board, and always work in a static-free workspace.

3.12.1 Overview

We'll be discussing things from two circuit boards: The MPU board (AS-2517-17 or -35) and the Solenoid Driver board (AS-2518-22 or -16). The solenoid driver gets signals from the MPU board. These signals tell the solenoid driver which solenoid to fire. Up to 15 momentary and 4 continuous solenoids can be controlled by the solenoid driver. The flipper solenoids are enabled or disabled from the solenoid driver too, but are not controlled like the other solenoids.

3.12.2 How the Solenoid Driver Works

The solenoid driver is responsible for energizing the solenoid coils of your pinball machine. Four signals from the U11 PIA integrated circuit on the MPU board travel out from the J4 to the J4 connector on the Solenoid Driver board. These four signals tell the Solenoid Driver which solenoid to fire. This is accomplished by using a decoder chip that takes the binary pattern of the four signals (16 different patterns) and decodes (or demultiplexes) them into one of sixteen different outputs. The four signals are applied to the decoder then the decoder is strobed. Normally, all sixteen of the decoder output lines are held high (+5 vdc). When strobed, the decoder lowers one of it's sixteen output lines, depending on the pattern of the four input signals. You can learn more about the 74LS154 decoder chip from here.

Take a look at the schematic below, which shows one typical output line and the associated circuitry to drive a single solenoid coil:

With no input supplied (strobe is high), the output lines of the decoder are high (+5 vdc). This puts a voltage at the base of Q1 (this transistor is one of 7 in the CA3081 chip). This turns Q1 "on" and the voltage supplied to it's collector via resistor R1 passes through the transistor to ground. At this point, little or no voltage is present at the base of Q2, and Q2 is "off". With Q2 off, the 40 vdc at the coil has no place to go, and the coil remains deenergized.

When the MPU board supplies the proper input signals (A-B-C-D) to the decoder, and the decoder is strobed (signal drops to low), the proper output signal will go low, which turns Q1 "off" (notice one of the two strobe lines goes to ground, so it's always low). This allows the +5 vdc at Q1's collector to flow through the diode instead of Q1 on it's way to ground via resistor R3. This also puts a voltage at the base of Q2 and turns this transistor "on". When Q2 turns on, the 40 vdc at the solenoid now has a path to ground through Q1 and current flows through the coil, thereby energizing it. Then the strobe to the decoder is released, the decoder output goes high again, Q1 turns on, Q2 turns off, and everything is back to normal.

Diode D1, resistor R3 and capacitor C1 work to slow the speed at which Q2 and the solenoid are able to turn off. This is important to prevent the "inductive kick" voltage that builds up when you try to turn off a solenoid quickly. A solenoid coil can build up hundreds of volts if it is switched off too quickly. For example, the spark in the spark plug of a car is generated from this inductive kick when the ignition coil is turned off quickly. In this case, D1 allows Q2 and the solenoid to turn ON quickly (which is OK) because the current that used to be flowing through Q1 can now flow forward through D1 and turn on Q2 quickly. However, when the decoder output goes back to high and Q1 turns back on, D1 prevents the charge from the base of Q2 from being sucked down Q1. The charge on C1 must drain off (slowly) through R3 and the base of Q2. This takes awhile and slows the turn-off of Q2 and the solenoid COIL, thus reducing the kick. Also, as the solenoid turns off and the voltage on the collector of Q2 starts to rise, this voltage is "fed back" by C1 to the base of Q2 and tends to keep Q2 on a little longer, slowing the turn-off of the solenoid even more. The OTHER diode (D2, across the solenoid) works to absorb the solenoid's turn-off kick by conducting when the voltage on the collector of Q2 is greater than about 40 volts.

3.12.3 Testing and Replacing Transistors

To test a transistor set you DMM to diode test mode. With the game turned off place the black lead on the metal tab of the transistor. Probe the two outer legs of the transistor with your red lead and the DMM should read between .4v and .6v (some DMM will show 4xx - 6xx). The center leg should be a dead short to the metal tab. If either outer leg reads anything but .4v to .6v then that transistor needs to be replaced. Use TIP-102 as the replacement transistor.

If a transistor needs to be replaced it is usually a good idea to check / replace the 1n4004 diode and 330 ohm resistor associated with that transistor as these will often burn / short. Also check the diode on the associated coil, it is likely to be shorted as well.

3.12.4 Solenoid Driver Upgrades

There are some upgrades that you can do to reduce stress on connectors.

There are two 5v test points on the SDB and these can be tied together. On the solder side of the driver board jump TP1 and TP3 together. Be careful you get the right test point. This eliminates a possible failure point on J3 pins 13 and 25. Note that test point one is for the raw +5 voltage coming out of the regulator, and test point three is for the voltage that feeds all the +5 circuits in the driver section. If there's a problem in the driver section, you can isolate it by removing this jumper and removing pin 13 or 25 from J3.

Next the C23 cap needs a common ground with the rest of the SDB. Jump the negative side of C23 to a convenient ground trace. On most boards there is a ground trace going right by the C23 negative lead, other boards might require a longer jumper. Scrape the solder mask off the trace to get a good solder surface to solder the wire to. If you're replacing the C23 capacitor (a good idea, they can be 34 years old at this point) you can sometimes leave the negative lead "long" on the capacitor and bend it down to the ground trace and solder it in both the mounting hole and the trace.

C26 needs a ground upgrade similar to what C23 got. Tie the negative side of C26 to the ground trace going along the outside of the board. This connects both C23's and C26's negative side to a common ground on the SDB. The goal of these modifications is to provide redundant grounds with the least resistance possible.

See this picture for a visual description of the upgrades.

3.12.5 How to Rebuild the Bally/Stern Solenoid Driver Board

The Solenoid Driver board is critical to the operation of the electronics of the game. The Solenoid Driver Board (SDB) comes in several types for Bally and Stern, and are completely interchangeable for any game of the 6800 MPU type. The SDB supplies the game with the voltages for the MPU, coils and high voltage for the displays. Recommendations are given below for replacing components to ensure proper operation and reliability. In all cases, do the ground modifications as shown in another part of this Wiki.

Minimum Recommendation for a Working board

At a minimum, replace both large capacitors on a working or non-working board, especially if they look original. Original caps are often metallic blue or metallic silver, and are at least 30 years old and due to fail, owing to the electrolytic chemicals in the capacitor drying up. The capacitor at C 23 has a factory value of 11,000 uf and 20 volts, but these values are not easily found these days. A electrolytic capacitor of between 11,000uf and 16,000 uf and 25 volts or greater can be safely substituted. A screw terminal capacitor makes for a easy installation, but a snap cap with leads can be used as well. Recent prices for screw terminal caps have increased greatly so this may be a factor in your decision.

The high voltage capacitor at C26 has an original spec of 160 uf and 350 volts and is a axial electrolytic capacitor. Once again, this part is difficult to encounter with these exact specs, but a axial or radial cap from 150uf to 180 uf and at least 350 volts can substitute. 400 v or 450v caps can be had in a radial format and size that will fit. With a radial cap you will have to make leads that bend back to the negative (-) solder pad.

Preferred recommendation for a working board

Besides the above, replace ALL the .100 and .156 molex header pins and the connector terminals in the nylon housings with Molex TRIFURCON Phosphor Bronze tin plated crimp terminals (Molex Part# 08-52-0113 for 18-20 ga. Wire, and 08-52-0125 for 22-26 ga.) for the .156 connectors, and Molex .100 tin plated Phosphor Bronze crimp terminals, (Molex Part#08-52-0123). Do NOT skimp on this step and just do one or the other. The receptacles if not burnt, can be re-used. If replacing the receptacles, the locking or non- locking ramp type are fine. Often, the connector at J5 does not cover the last few pins. I don’t like this personally, although no harm can be done IF the key is in place.

Check every resistor that is usually covered by the plastic shield between the two big heat sinks for correct value and no sign of burn. Replace any that are suspect. Use the diode function on your multimeter to check the zener diode at VR1 and the 1N4004 diode. The zener diode can be difficult to source. See below for recommendation.

Gold Standard for Working or NON-WORKING board

It doesn’t make too much sense trying to trace down the exact problem and replacing only the bad components on a NON-WORKING board. Better to replace every possible bad component and start fresh. To ensure long life and proper operation of a working board, in ADDITION TO THE ABOVE, it is recommended that the components below are replaced regardless. Below is a list of components that effect the HV and +5 volt logic circuits on the SDB. Replace them all ! * The Stern Revision J board is rather different, & a component list for that board follows. It can be identified by the extensive silk screening of each component and its function as seen in the 4th photo above, and by the HUGE 2 Watt and (2) large 1 Watt resistors. It is most often found on late date Stern games like Flight 2000 or Viper, etc.

Component replacement list for Bally AS2518-16 or -22 and Stern SDU100 SDBs, except * revision J

Resistors

• R51 22k ohm 1/2Watt
• R52 390 ohm 1/4 Watt
• R54 8.2k ohm 1/4 Watt
• R55 1.2k ohm 1/4 Watt
• R56 82k ohm 1/2 Watt
• R35 100k ohm 1 Watt

Diodes

• CR21 1N4004 400PIV 1 amp or better (1N4007, etc.)
• VR1 Zener diode 1N5275A 140 volts, 1 Watt. Can Sub NTE 5099A

Transistors

• Q21 2N3584 250volts, 2 amp, TO-66 NPN
• Q22&23 2N3440 250 volts 1 amp TO-39 NPN
• Q20 LM323k (original 78H05KC or LAS1405)

Capacitors

• C27&28 .01 uf 400 vdc metal polyester capacitor

• RT1 25k ohm potentiometer (2 types) a 15mm black one, Piher Part# PT15LH06-253A2020 or a 6mm blue one BournsPart#3306P-1-253

Stern SDU100 revision J

• R35 100k ohm 1 Watt
• R51 33k ohm 2 Watt
• R52 390 ohm 1/4 W
• R53 2.4k ohm 1/4 W
• R54 8.2k ohm 1/4 W
• R55 1.2k ohm 1/4 W
• R56 82k ohm 1/2 Watt
• R73 3.3 ohm 1/4 W
• R74 470 ohm 1/4 W
• R75 100k ohm 1 Watt
• CR22 1N4004 or better
• Q24 2N3904 Transistor

Other diodes, transistors and capacitors as above for AS2518-18

3.12.6 Modify the Display Fuse holder

Fuse adapter for the SDB allowing use of a common fuse

The display fuse on the Solenoid Driver board is a difficult to find and expensive type 8AG 3/16 amp fast blow. It would be best when rebuilding the SDB to replace the fuse holder with new clips and convert it to a more commonly available 3AG type. The original value of 3/16 amp can be substituted with a more common 1/4 amp without worry of over fusing the circuit, due to inherent variations of tolerance by the manufacturer.

All that needs to be done is;

• bend up or clip off the upper solder lead of the clip
• move the TOP fuse holder up one hole
• solder a 20 ga. wire from the base of the clip back down to the lower hole.
  

Be careful not to solder the clips with the inner "ears" facing in the wrong direction, or you will need to re-do your work. It may be helpful to put an old 3AG fuse in the clips to aid in spacing, assure that the "ears" are positioned correctly, and hold the clips in place while soldering. See the photo above. Of course, an inline fuse holder can also be used instead, but looks less professional.

3.13 Bally 6-Digit Displays

This section will help you understand and repair your Bally 6-digit displays. The information is focused on the AS-2518-21 display. Since the AS-2518-15 display is interchangeable with the "-21" display, everything mentioned here will apply to both displays. 7-digit displays behave the same too, so this information will be helpful for those too. The only real difference is an additional digit enable signal, and some more electronics on the board to drive the 7th digit.

If you could care less how they work, but are looking for information on how to repair them, then jump to the Repairing Bally Displays article below. We'll also show you some ideas on how to keep your displays working properly.

A healthy Bally 6-Digit Display

Examples off a Bally AS-2518-21 6-digit display, and a Bally AS-258-15 6-digit display:

You can see that the two displays are a little different in the way the components are laid out. Regardless of the differences in appearance, they both perform the same function and are interchangeable with each other The original display (at least the one mentioned in my Power Play Owner's Manual) is the "-21". The two shown here were upgraded with 1/2 watt 100K ohm resistors. A modification that you should do on all your displays too.

Here are some Stern displays that will work in place of the two above:

3.13.1 How the displays work

The way the display circuitry works is really quite interesting. Although the human eye can not detect it, at any given moment, each display is only showing one digit at a time. The program that runs on the machine's computer is changing the digits so fast that you can not tell. If you were to film the displays and play the film back in slow motion, you'd see all the displays showing the same digit, and it cycles through all six, from left to right. It just cycles so fast that your brain thinks the whole display is lit all the time.

As you can see, each display has six digits, and if you look closely, you can see that each digit consists of seven segments. This is important stuff to know in order to understand how these displays work, and most important, how to fix them cheaply!

If you study the display's schematic, you can see that there are 4 main "parts" of a display assembly: The glass display itself, and the display driver consisting of the input decoder, six digit driver circuits, and seven segment driver circuits. There is one digit driver circuit for each of the six digits, and one segment driver circuit for each segment of a digit. How the actual glass display does what it does in order to light various digits and segments is beyond the scope of this tutorial, so we'll ignore that. The decoder takes a number from 0 - 9 as input and determines which segments need to be energized in order to represent this number. The digit drivers are responsible for applying the proper voltages to the proper pins of the display to tell it which digit to light. The segment drivers are responsible for applying the proper voltage to the proper pins of the display to tell it which segments of the digit to light. It is the MPU's job to supply the proper signals to the display driver to make it do all this stuff.

The decoder is a small integrated circuit (MC14543LE) called a "BCD To Seven Segment Decoder". This decoder happens to be a "latching" decoder, which means it latches on to it's inputs and keeps them, even if they are no longer applied, until the decoder is told to release them (blanked). The decoder also has an input called a strobe. When strobed, the decoder will read it's four inputs and latch on to them. A strobe signal is usually a quick off/on/off pulse. There is also an input for the blanking signal.

BCD stands for Binary Coded Decimal and is a fancy term for storing a number from 0 - 9 in a half byte of storage (four bits). Using BDC encoding, each byte of memory can store two digits. Anyway, the input of the decoder is a BCD number from 0 - 9, and the output of the decoder is seven signals. These seven signals are either on or off, and relate to the seven segments of a digit. Each of the seven output signals go to a MPS-A42 transistor, which is part of a circuit called a segment driver. This transistor acts like a switch to turn the segments on or off. The outputs of the seven segment drivers go to the seven segment pins of the display glass. So this is how the computer tells the display driver which segments to light. The MPU has a four-signal data path that goes to all five displays (or seven for Six Million Dollar Man). These four signals provide the 4-bit input into the decoder, and remember, all four signals go to ALL of the displays. Below is a diagram of how the segments are labeled, and a truth table showing the 15 possible inputs and outputs to the decoder. For those of you that don't know about binary arithmetic, you can get 15 possible combinations of on/off with 4 digits. (e.g., "0000", "0001", "0010", ..., "0111", "1111"). This is also how you count in binary, or base-2. Remember that the display driver is only interested in 10 of the 15 possible combinations, the ones that represent the numbers 0 - 9, or "0000" - "1001". Any other input combinations will result in unpredictable outputs from the decoder, so we label these as "don't cares", since we know they will never happen under normal circumstances.

The digit driver circuit consists of an MPS-A42 transistor and a 2N5401 transistor connected in a circuit that acts as a switch. Normally with no input signal applied, the switch is off, keeping the high voltage supplied by the HV Regulator away from the display. There are 6 digit signals provided by the MPU, one for each digit. The MPU will enable one signal at a time, telling the display driver which digit to operate. This signal will then turn on the "switch" for the digit, allowing the high voltage a connection to the proper pins of the glass display to energize the desired digit. These signals from the MPU are simply 6 wires and the MPU will activate one of them at a time. Like the segment signals, the six digit signals go to all of the displays in a daisy chain fashion.

OK, before I explain how the computer makes all this work, let's sum up: A display driver has four inputs from the MPU. The first is a collection of six signals used to tell the display driver which digit to energize (six digits in the display, six digit signals). Only one of these signals are on at a time. The second input is a collection of four signals that tell the display driver which number to display, in the form of segments. These four signals provide a binary pattern that is interpreted as a binary number from 0 to 9. The third input is a strobe signal, which tells the decoder to read it's inputs, and the fourth signal is a blanking signal, which tells the decoder to turn off all it's outputs. Also, but not mentioned above, are various voltages from the power supply and high-voltage regulator. Each display driver is supplied with +5VDC from the 5-volt regulator on the solenoid driver board. This is used to drive the logic circuits of the decoder. There is also +190VDC* applied to the display driver from the high-voltage regulator on the solenoid board. Finally there is a connection to ground, which brings all the voltages to the proper reference point.

• For brand new displays, this voltage should be at +190VDC in order to "burn in" the display. Once a display has become used, this voltage may be backed down to +170VDC, which will work just fine and will help prolong the life of the display.

3.13.2 How The Computer Controls The Display

OK, so now you know how the display works. The next thing to understand is how the computer in your pinball machine operates the displays. For this article, we'll referring to the AS-2518-17 Bally MPU Module, but all this also holds true for the "-35" MPU module as well. And again, I'm only referring to the Bally AS-2518-21 and AS-2518-15 Display Drivers. The Stern style display drivers operate the same, and the six digit stern drivers are 100% swappable with the Bally displays. There are a few minor differences between the seven digit varieties of displays preventing a direct swap without modifications.

As mentioned above, there are four sets of signal lines that go from the MPU module to the display driver modules. The first set is the BCD data set which carry the display segment BCD data to all the displays on 4 wires. They leave the MPU module (A4) at connector J1, pins 25-28 and visit every display driver module at connector J1 and pins 16-19 (D4 - D0). The next set of signals is the digit enable signals. These 6 wires carry signals to all the display driver modules with information telling it which digit to light. The third set of signals are 5 latch strobe signals. There is one separate signal for each display driver, and it is the signal that tells the driver's decoder to read the decoder inputs, and output the proper segment signals. The final signal is a single single that goes to all the display drivers called Display Blanking. The signal tells the display driver's decoder to turn off all segment outputs, thereby blanking out the display, or turning all segments off. Below is a diagram of all the connections between the MPU module and the display driver modules that have to do what we're talking about.

Once the machine has been turned on and has booted up, the processor on the MPU module is continuously running a program that is stored in the module's ROM chip(s). This program is responsible for controlling the game by reading all the switches, lighting all the lamps, activating all the solenoids, and controlling the displays. The program keeps a lot of information in RAM and uses this information to keep track of scores, switches, etc. An interrupt is a term for a section of computer program that interrupts the "main" program in order to execute a smaller program, sometimes referred to as a "service routine". We won't get into just how this actually happens, just be aware that the main program of a computer may be interrupted at any given time. And to make things even more complicated, interrupts themselves can be interrupted by higher priority interrupt service routines. There may be several different interrupts that occur in a pinball's computer program, but the one we want to study is the one that controls the displays. Keep in mind what was mentioned above, that at any given instant, only one digit is lit on any display. This is called multiplexing.

320 times a second, or once every 3-1/4 milliseconds (thousands of a second), the CPU is interrupted to service the displays. In memory, the CPU keeps track of all the information it needs to operate all the displays. This information includes a counter used to indicate which display digit is active, the BCD data for all the displays, etc. Here's what the display service routine actually does:

Determine which digit was updated last time - The MPU looks at the digit counter and adds 1 to this value. If the new value is 7, it is changes to 1, then the new value is stored back into memory. Let's assume the new value is 4, so we're going to update the 4th digit.

Blank out all the displays - The CPU raises the signal on the Blanking Line which causes all displays to go blank (the blanking signal tells all the decoders to turn off their segment outputs).

Fetch the BCD data from memory - The BCD data for the first display, 4th digit is fetched from memory.

Send the BCD data to the display driver - This BCD data is placed on the BCD data bus and display #1 is strobed. This will cause the display's decoder to latch onto the input signals (store them for future use).

'Do it again - The previous two steps are repeated for the second, third, fourth, and fifth display.

Enable the digit - The MPU then enables the 4th digit and disables the other 5 digits by raising and lowering signals on the Digit Enable lines.

Finally, turn the digit on - The MPU lowers the signal on the Blanking Line, which causes the all of the decoders to output their proper segment signals and the 4th digit on each display is displayed.

All done! - The interrupt service routine then exits and control returns to the main program

As you can see, the display interrupt service routine only handled 1 digit for all displays. Every time it is invoked, it will process the "next" digit, resetting the counter back to 1 when necessary. The process of updating 1 digit for all displays takes about 500 microseconds, or 1/2 of a millisecond, to complete. Pretty cool, eh?

So, lets do some math. It takes 1/2 millisecond to update one digit, and since there are 6 digits, it takes 3 milliseconds to display all six digits. Since the interrupt runs 320 times a second, and it takes 6 interrupts to update the entire display, dividing 320 by 6 means that the displays are completely updated just over 54 times every second. That's fast enough to fool your eyes and brain into thinking the display is completely lit all the time. Also, since the interrupt routine takes about 1/2 millisecond to run, and it runs 320 times every second, that means about 160 milliseconds of every second of time is spent updating the displays, which is about 16 percent of the time.

3.14 Rectifier Boards

3.14.1 How To Hook Up a Bally AS-2518-18 Rectifier Board

Often folks buy a new or used rectifier board and then when they get it, they realize that they have to hook it back up to the old wiring harness. If this is you, and you forgot to take notes or pictures before you removed your old board, then here you go. The photo below shows an original AS-2518-18 rectifier board connected to a factory wiring harness. As far as I know, the wire colors are the same for ALL AS-2518-18 applications.

Key:

E1 - Red 18 AWG - Transformer Lug 5 - Primary AC Hot

E2 - Yellow 18 AWG - Transformer Lug 1 - Primary Neutral

E3 - Red 20 AWG - Transformer Lug 2 - Solenoid Bus Hot

E4 - White/Red 20 AWG - Transformer Lug 6 - Solenoid Bus Neutral

E5 - Green 20 AWG - Transformer Lug 8 - Display High Voltage Hot

E6 - White/Green 20 AWG - Transformer Lug 10 - Display High Voltage Neutral

E7 - Blue 18 AWG (2 wires) - Transformer Lug 17 - GI Bus Hot

E8 - Black 18 AWG (2 wires) - Transformer Lug 18 - GI Bus Neutral

E9 - Orange 18 AWG - Transformer Lug 13 - Controlled Lamp Bus Hot

E10 - Green 18 AWG - Transformer Lug 14 - Controlled Lamp Bus Neutral

E11 - White 20 AWG - Transformer Lug 15 - 12V Input for 5-Volt Regulator Hot

E12 - White/Black 20 AWG - Transformer Lug 16 - 12V Input for 5-Volt Regulator Neutral

AWG = American Wire Gauge (18 = fat, 20 = skinny)

"E" solder pads are labeled on the top side of the circuit board

3.14.2 How To Hook Up a Stern TA-100 Rectifier Board

As Steve mentioned above when you replace or remove and reattach your rectifier board you need to know how to hook it back up. I have done this with a lot of Stern pins and made myself a chart for quick and easy reference when re-attaching the rectifier to the transformer. I figured it may be useful to others as well.

3.15 Bally Auxiliary Lamp Driver Boards

Bally AS-2518-52 Aux. Lamp Driver Board

Bally AS-2518-43 Aux. Lamp Driver Board (Midway A084-91614-A000 pictured - same as AS-2518-43)

3.16 Bally Sound Boards

3.16.1 Bally AS-2518-32 Sound Board

Bally AS-2518-32 Sound Board

3.16.1.1 -32 Sound Board ROMs & Jumper Settings

Game	U3 ROM	Jumper Settings
Lost World	E729-18	B
Six Million Dollar Man	E729-18	B
Playboy	E729-18	B
Voltan Escapes Cosmic Doom	?	?
Supersonic	E729-18	B

Source: Bally / Midway 1982 parts catalog.

3.16.2 Bally AS-2518-50 Sound Board

Bally AS-2518-50 Sound Board

3.16.2.1 -50 Sound Board ROM & Jumper Settings

Game	U3 ROM	Jumper Settings
Star Trek	E729-18	B, D
Kiss	E729-18	B, D
Paragon	E729-51	B, C
Harlem Globetrotters	E729-51	B, C
Dolly Parton	E729-51	B, C

Source: Bally / Midway 1982 parts catalog.

3.16.3 Bally AS-2518-51 Sound Board

Bally AS-2518-51 Sound Board

3.16.3.1 -51 Sound Board ROMs & Jumper Settings

Jumper A is used when U3 is a 6802 and U10 (6810) is not used.
Jumper B is used when U3 is a 6808 and U10 (6810) is used.
Jumper C is used when U4 is 2K in size (9316B or 2716).
Jumper D is used when U4 is 4K in size (2532 or 4732).

Game	U4 ROM	Jumper Settings
Future Spa	E781-2, E781-5 (or sub with E781-13)	B, C
Nitro Groundshaker	E776-14, E776-15	B, D
Silverball Mania	E786-8, E786-11	B, C
Space Invaders	E792-2, E792-7	B, C
Rolling Stones	E796-11, E796-19	B, C
Mystic	E798-2, E798-5	B, C
Hot Doggin	E809-2, E809-7	B, C
Viking	E802-2, E802-7	B, C
Skateball	E823-2, E823-14	B, C
Frontier	E819-2, E819-9	B, C
Speakeasy	E877-1	B, C
BMX	E888-02	B, D

Source: Bally / Midway 1982 parts catalog.

3.16.4 Sounds Plus Sound Board (AS-2518-56)

The Sounds Plus board was only used in Xenon and very early Flash Gordons. The Sounds Plus board has a daughter card called the Vocalizer that contains the roms and circuitry needed to generate speech.

3.16.5 Squawk & Talk Sound Board

AS-2518-61 Squawk & Talk Sound Board

The Squawk & Talk (S&T) sound board was the first to offer sound and speech in one board to Bally games. It is probably the most intuitive sound board Bally offered too. Similar to the Bally MPU boards, the S&T uses an LED flashing system during board initialization. There are at least 3 variations of the board: -61, -61a, and -61b.

AS-2518-61a Squawk & Talk Sound Board

3.16.5.1 Squawk & Talk Jumper Settings

The first table below, is a list of the Squawk & Talk jumper settings by game as specified in the 1982 Bally / Midway parts catalog. These jumpers reflect the original ROM configuration when the game was released. If you've changed your sound ROMs to 2716s or from 2532s to 2732s, see the second table below.

• If using a 6808 CPU chip, install L, remove K
• If using a 6802 CPU chip, install K, remove L
• The 5 EE jumpers must be installed when the AY-8912 chip is not present.
  

Game	Jumper Settings
Flash Gordon	C, D, E, G, Q, S, U, W, Y, AA, H, DD, N, L OR K
Eight Ball Deluxe	C, D, E, G, Q, S, U, X, Y, AA, H, DD, N, L OR K
Fireball II	C, D, E, G, Q, S, U, X, Y, AA, H, DD, N, L OR K
Embryon	C, D, E, G, Q, S, U, X, Y, AA, H, DD, N, L OR K
Fathom	C, D, E, G, Q, S, U, W, Y, AA, H, DD, N, L OR K
Medusa	C, E, G, Q, S, U, W, Y, BB, D, H, DD, N, EE, L OR K
Elektra	C, E, G, Q, S, U, W, Y, BB, D, H, DD, N, EE, L OR K
Centaur	C, E, G, Q, S, U, W, Y, BB, D, H, DD, N, EE, L OR K
Rapid Fire	C, E, G, Q, S, U, W, Y, AA, H, EE, CC, M
Mr. & Mrs. Pac-Man	C, D, E, G, Q, S, W, Y, U, AA, H, DD, N, L OR K
Spectrum	C, D, E, G, Q, S, U, W, Y, BB, H, DD, N, EE, L OR K
Vector	C, D, E, G, Q, S, U, W, Y, AA, H, DD, N, L OR K

Source: Bally / Midway 1982 parts catalog.

ROM Size/Location	U2	U3	U4	U5
2716	D, P	Q, T	U, X	Y, BB
2532	D, G	Q, S	U, W	Y, AA
2732	F, P	R, T	V, X	Z, BB

3.16.6 Say It Again Board

File:AS-2518-81-2.jpg

Bally AS-2518-81 Say It Again Sound Board

The "Say It Again" sound board is a board used to add reverb to a Squawk & Talk sound and speech board. This board was only used on Centaur and Centaur II.

3.16.7 Cheap Squeak Sound Board

Bally Cheap Squeak Sound Board A080-91603-XXXX or Midway P/N M-051-00114-XXXX

LED boot up flash sequence is four flashes. Two quick, pause, two more quick. After boot up the LED seams to go on and off when sounds are playing or idle.

Cheap Squeak is used in the following games:
Black Pyramid - Cybernaut - Fireball Classic
King Of Steel - Spy Hunter - X's & O's
----------------------------------------------
EPROM Configuration	Jumpers Connected
U3&U4 using 2532s	J6, J9, J12
U3&U4 using 2732s	J7, J10, J11
U3 ONLY using 2764 (may not work in all games)	J2, J4, J7, J11

3.16.8 Turbo Cheap Squeak Sound Board

3.16.9 Sounds Deluxe Sound Board

3.16.10 Bally Sound Board Pinouts

Pin Connection	AS-2518-32	AS-2518-50	AS-2518-51	AS-2518-56 Sounds Plus	AS-2518-61 Squawk & Talk	AS-2518-61A Squawk & Talk	AS-2518-61B Squawk & Talk	A080-91603-C000 Cheap Squeak	A080-91855-C000 Turbo Cheap Squeak	A084-91864-C000 Sounds Deluxe
J1-1	Sol. Address A	Sol. Address A	Sol. Address A	Sol. Address A	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 0	Sound Select 0
J1-2	Sol. Address B	Sol. Address B	Sol. Address B	Sol. Address B	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 1	Sound Select 1
J1-3	Sol. Address C	Sol. Address C	Sol. Address C	Sol. Address C	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 2	Sound Select 2
J1-4	Sol. Address D	Sol. Address D	Sol. Address D	Sol. Address D	Sound Select	Sound Select	Sound Select	Sound Select	Sound Select 3	Sound Select 3
J1-5	+5VDC	+5VDC	+5VDC	+5VDC	N/U	N/U	N/U	N/U	N/U	N/U
J1-6	Ground	Ground	Ground	Ground	Ground	Ground	Ground	Logic Ground	Logic Ground	Logic Ground
J1-7	N/U	N/U	N/U	N/U	Gen. Ill. Bus (6VAC)	Gen. Ill. Bus (6VAC)	Gen. Ill. Bus (6VAC)	N/U	N/U	N/U
J1-8	Sol. Bank Select	Sol. Bank Select	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt
J1-9	+43V	+43V	N/U	N/U	N/U	N/U	N/U	N/U	N/U	N/U
J1-10	N/U	N/U	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+14V Unregulated	+14V Unregulated
J1-11	Key	Key	Key	Key	Key	Key	Key	Key	Key	Key
J1-12	Sol. Address E	Sol. Address E	Sol. Address E	Sol. Address E	Sound Select	Sound Select	Sound Select	N/U	N/U	N/U
J1-13	N/U	N/U	N/U (Spare Address Line)	N/U (Spare Address Line)	N/U	N/U	N/U	Earth Ground	Earth Ground	Earth Ground
J1-14	Ground	Ground	Ground	N/U (Ground)	Ground	Ground	Ground	Logic Ground	Logic Ground	Logic Ground
J1-15	+43V Return (Sol. Ground)	+43V Return (Sol. Ground)	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+12V Unregulated Return	+14V Unregulated Return	+14V Unregulated Return
J1-16	n/a	n/a	n/a	n/a	n/a	+12V Unregulated Return	+12V Unregulated Return	n/a	n/a	n/a
J1-17	n/a	n/a	n/a	n/a	n/a	+12V Unregulated	+12V Unregulated	n/a	n/a	n/a
J1-18	n/a	n/a	n/a	n/a	n/a	N/U	N/U	n/a	n/a	n/a
Pin Connection	AS-2518-32	AS-2518-50	AS-2518-51	AS-2518-56 Sounds Plus	AS-2518-61 Squawk & Talk	AS-2518-61A Squawk & Talk	AS-2518-61B Squawk & Talk	A080-91603-C000 Cheap Squeak	A080-91855-C000 Turbo Cheap Squeak	A084-91864-C000 Sounds Deluxe
J2-1	Speaker +	Speaker +	Speaker -	Speaker -	Speaker -	Speaker -	Speaker -	Speaker -	Speaker Return	Speaker Return
J2-2	Speaker -	Speaker -	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +
J2-3	n/a	n/a	n/a	n/a	Key	Key	Key	n/a	Key	n/a
J2-4	n/a	n/a	n/a	n/a	Remote Volume Return	Remote Volume Return	Remote Volume Return	n/a	N/U	n/a
J2-5	n/a	n/a	n/a	n/a	Speech Volume	Speech Volume	Speech Volume	n/a	N/U	n/a
J2-6	n/a	n/a	n/a	n/a	Sound Volume	Sound Volume	Sound Volume	n/a	N/U	n/a
J2-7	n/a	n/a	n/a	n/a	n/a	n/a	Reverb Audio In	n/a	n/a	n/a
J2-8	n/a	n/a	n/a	n/a	n/a	n/a	Shield Ground	n/a	n/a	n/a
J2-9	n/a	n/a	n/a	n/a	n/a	n/a	Audio Out	n/a	n/a	n/a
J2-10	n/a	n/a	n/a	n/a	n/a	n/a	Shield Ground	n/a	n/a	n/a
Pin Connection	AS-2518-32	AS-2518-50	AS-2518-51	AS-2518-56 Sounds Plus	AS-2518-61 Squawk & Talk	AS-2518-61A Squawk & Talk	AS-2518-61B Squawk & Talk	A080-91603-C000 Cheap Squeak	A080-91855-C000 Turbo Cheap Squeak	A084-91864-C000 Sounds Deluxe
J3-1	n/a	n/a	n/a	n/a	n/a	n/a	Ground	n/a	n/a	n/a
J3-2	n/a	n/a	n/a	n/a	n/a	n/a	Data	n/a	n/a	n/a
J3-3	n/a	n/a	n/a	n/a	n/a	n/a	Clock	n/a	n/a	n/a
J3-4	n/a	n/a	n/a	n/a	n/a	n/a	+5VDC	n/a	n/a	n/a
J3-5	n/a	n/a	n/a	n/a	n/a	n/a	Key	n/a	n/a	n/a
J3-6	n/a	n/a	n/a	n/a	n/a	n/a	PB3	n/a	n/a	n/a
J3-7	n/a	n/a	n/a	n/a	n/a	n/a	PB2	n/a	n/a	n/a

3.17 Stern Sound Boards

3.17.1 Stern SB-100 Sound Board

Stern SB-100 Sound Board - 1st Version

Stern SB-100 Sound Board - 2nd version (less populated)

3.17.2 Stern SB-300 Sound Board

Stern SB-300 Sound Board

4 Problems and Solutions

4.1 Powering up the first time

Thanks to Bally's decision to modularize their system, there is a technique you can use to save yourself some headaches when you first power up a machine. This method connects one section/board at a time and allows you to test each board thoroughly before moving onto the next so you can isolate any issues to one board. This method concentrates on the -18, -49, and all stern games rectifier boards. The -54 rectifier board on later Bally games would employ a slightly different technique.

Disconnect all connectors from the mpu, lamp, sound (if present) and solenoid driver boards. Disconnect J1 and J3 from the rectifier board. Leave J2 connected. Check all the fuses for proper values on the rectifier board. Power on the game, watching to see if any fuses blow. Use a meter and test each test point on the rectifier board to ensure proper voltage is present (remember some of the voltages are AC). Get the rectifier board working 100%.

Turn the game off and reconnect J3 to the solenoid driver board. Connect J3 to the rectifier board as well. Power on the game and repeat the voltage tests on all the test points on the rectifier and solenoid driver board. Investigate any suspect voltages and correct any faults found. Keep in mind that the displays use both the high voltage and +5 voltage so it might be a good idea to remove the displays from the circuit, also.

Once the solenoid driver board tests ok, connect J4 to the mpu board. Do not reconnect any other connectors to any other boards at this point. Power on the game; if all is well, you will see the mpu board start its LED flash sequence. This is where the majority of repairs will take place; there's no point in hooking other boards up until you have a solid rectifier, solenoid driver/power regulator, mpu board combination working.

After/if the mpu board is booting, add the rest of the connectors back in. When you add the playfield's connectors back in and power up, listen for any solenoids locking on at power-up. Repair the solenoid circuits before proceeding if any do lock on.

At each step in the chain, be sure to inspect and repair any and all connectors in the circuits. Often the connectors get tarnished and do not conduct well enough for reliable game operation. Do not try to clean or sand any suspect connectors - this is a temporary fix at best and only delays the inevitable task of replacement.

Using this method for powering up the game for the first time ensures that any issues you encounter will be isolated to the last piece you added in. Diagnosing and repairing one board at a time is much simpler than multiples.

4.2 Rectifier Board Issues

4.2.1 -18, Stern Rectifier boards

The rectifier board takes the AC voltage from the transformer and uses bridge rectification to convert those voltages to DC. No filtering is done on the rectifier board (that's the solenoid driver/power supply board's job). Depending on the generation of board, there are varying amounts of discrete diodes or bridge rectifiers that produce the DC voltages needed. Additionally, all of the circuits have a fuse for protection in the event of a short on this board.

Putting a meter on the test points across the top of the board will tell you if you're missing any voltages. Refer to the schematics or the charts above to determine the proper voltages at each test point, and remember that some of the voltage outputs are AC volts. If there are any missing voltages investigate further to determine the cause. The main issues with the rectifier board are cracked header pins, bad bridges, poor fuse clips, and poor connections on through hole vias.

If you do nothing else to your power supply, replace the header pins and the connectors that connect to them. The pins are usually burnt beyond usage as are the connector pins. (Often, operators chopped the harness connectors off and soldered the wires directly to the pins as a "fix".) You can get 10 amp header pins from various suppliers that are more robust than the original 7 amp versions. Often just this change alone will fix many lamp "wavering" problems you see on games with lots of feature lamps.

When you replace the header pins consider prying up the plastic insulator piece slightly that keeps the pins in place so you can solder to the top and bottom of each pin. This technique will cure any problems with vias you have and obviate the need for jumper wires that accomplish the same thing. After soldering you can push the insulator piece back down.

Many times the fuse clips are weak or aren't making good contact with the fuses. If you inspect the fuse clips and they are tarnished at all, replace them. Any fuse rated at 4 amps or more use a high current fuse clip to eliminate issues in the future with that circuit. Lower value fuses can use lower current clips with no problem. Solder the fuse clips bottom and top where appropriate for maximal mechanical strength and conductivity.

It's a good idea to replace the discrete diode bridge for the high voltage score display with 1N4007 diodes mounted slightly off the board (about 1/4") so that air can circulate all around them. Solder the leads top and bottom where appropriate. The power resistors should be replaced also with a slight air gap below them to help with cooling. It is possible to approximately double the size of the power resistors (25 ohm to 47 ohm, 600 ohm to 1.3k ohm) to help with the heat dissipated Resistor/temperature discussion although the final test results were not posted.

If you need to replace any bridges, the original style VJ248 bridge can be replaced on the -18 board with a wire lead 25 or 35 amp bridge rectifier. The notch in the bridge is the positive + output; diagonally opposite this lead is the DC negative -. The other 2 leads are the AC inputs and are interchangeable. You have to bend the leads slightly to get them to fit in the smaller VJ248 solder pads. Mark the top of the board with the positive, negative, and AC leads so you don't solder the bridge off by mistake.

If you decide to use the original style bridge, make sure it's not thicker than the other bridges in any other position. The 3 bridges must lie flat against the heat sink slug for proper cooling. The best way to install a replacement VJ248 of the same thickness is to put the bridge in place, then bolt the slug back onto all 3 bridges. Solder the replacement bridge in place. Reinstall the slug with heat sink compound (available at computer supply stores or Radio Shack) smeared in a single thin layer on each bridge surface, and the slug surfaces. Use the least amount position to get a good even layer; more is not better.

After replacing any parts, test your work with only the J2 cabinet connector installed. Never over fuse a circuit unless the manual for the game specifies; for instance, games with more than 2 flippers often recommend a larger fuse for the solenoid circuit to handle the additional load multiple flipper coils place on the fuse.

4.2.2 -54 Rectifier board

The weak link of this generation of rectifier board are the CR1-CR4 diodes (originally 1n4004, replace with 1n4007) and CR5-CR8 (6 amp at least 50v diodes). The original bridges are much hardier on this generation of rectifier board. If you do need to replace a bridge, the best way is to install it and bolt it onto the bottom mounting plate, then solder it into place. The bottom mounting plate acts as a heat sink for the bridges.

BR1 is for the feature lamps on the game, BR2 is for the solenoids. The bridge formed by CR5-CR8 forms the +5 vdc, and the one formed by CR1-CR4 supplies the high voltage for the displays. Mount the discrete diodes slightly off the board for better cooling. While not a large problem on this board, inspect the fuse clips as well to ensure they are not tarnished.

4.3 MPU boot issues

Non-booting Bally/Stern MPU boards fall into a couple different categories. If the board's LED is good and turns off at bootup, you're part of the way there. Refer to the flash sequence section to figure out where your issue lies to narrow down the problem area.

You must have a good set of roms in a game as well as a known good working 6800 cpu chip. Suspect any sockets that have a brown color or closed frame - often the spring tension on these sockets is poor necessitating replacement. Be very careful soldering on the mpu boards as the traces and pads are very fragile.

4.3.1 LED locked on

First off, ensure that there's not simply a problem with Q2 or the LED itself (i.e. the board isn't actually booting up anyway, just with the LED locked on). A logic probe on pin 18 of the U11 6821 PIA will tell you if the LED signal is changing.

You can short pins 40 and 39 momentarily on the cpu chip; after doing so, see if the LED goes off. If it does, concentrate your efforts on repairing the reset circuit as it's not holding the reset low on powerup for the minimum required 50 milliseconds. If it doesn't, it's best to pull the board from the machine and put it on the bench, using the benchtop power supply details to keep working on the board outside the machine.

Attach a logic probe to the output of Q5 - on power on, you should see this circuit start low and then go high approximately 50 milliseconds later. If it goes high immediately, at a minimum replace Q5, then Q1. If you see the reset circuit working properly, next put the probe on U9 pin 3, 36, and 37 to see if you get pulsing - these are all clock signals and you should see pulsing on all 3 pins. If you have an oscilloscope you can visually see the signals, or even on a multimeter, the voltage will show between 2.5-2.9 volts. If you see zero volts or 5 volts, your clock signal is bad.

Try removing U7, U8 (U8 and U13 on Stern MPU-200 boards) and U10 to see if the board will then turn off the LED. This tells you the roms are being read and that one of the RAM chips or U10 PIA might be bad. Narrowing down what causes the lock on determines your next steps.

At this point if the LED is still locked on take a known good Bally U6 chip, re-jumper the board for 2x2732 roms, and put it in U6. If the mpu board now unlocks, add chips back in including a known good Bally U2 chip (or 2x2732 known good Stern chips) and you should get the unlock + 1st flash (Rom checksum ok).

Still locked on? After double checking all your jumper changes, roms, and rams in another board if possible, time to start suspecting other issues such as bad sockets, traces, or addressing chips.

4.3.2 Reset Circuit

The purpose of the reset circuit is to ensure the +5 vdc is stable before allowing the system to start. At startup, the reset signal is held low via pull-down resistor R139 until the +12 vdc line rises above the zener diode VR1's value (8.2 or 9.1 volts depending on your board). At this time, the input voltage threshold for the +5 regulator on the solenoid driver board has been met with some headroom. Q1 starts conducting, turning on Q5, which provides the actual reset signal. All of this happens in approximately 50 milliseconds.

Most of the reset circuit is in the corrosion zone (lower left corner of the mpu board) and consists of most of the components commonly included in "repair kits". If the reset circuit is not working, the LED will not turn off. If Q1 or Q5 fails, conducting all the time, the cpu chip will never come out of reset.

The reset circuit continuously monitors the +12 volt line; if it falls below VR1's threshold voltage, the game will reset. If a Bally/Stern game is resetting, concentrate on why the +12 volts is dropping below 8.2/9.1 volts. (VR1 sets the threshold at which the reset signal turns on, and also when it would turn off in a rebooting scenario.)

Note that Q1 and Q5 actually form a switching power regulator for the reset signal only. The normal +5 supplied to the rest of the board is derived entirely from the solenoid driver board's regulator. The reset signal regulated power is used to charge the battery, provide the reset signal, and to power the 5101 chip(s) on the board. Normal +5 vdc from is blocked from entering the reset circuit by the 1N4148 diode CR7. Diode CR5 (1N4148) blocks the battery voltage from powering the entire board via CR7.

4.3.3 Sockets

this is a stub

4.3.4 ROMs/ICs

this is a stub

The Motorola part number equivalencies that appear on the top of U9, U10, and U11 are...

• SC44216P = 6800 microprocessor
• SC44067P = 6820 PIA

4.3.5 Clock Signal

replacement 9602 board: http://www.homepin.com/9602.html

replace with a 6802: http://pinballeon.com/6802/e6802.htm

<WIP>

4.3.6 How to make a Benchtop power supply for the MPU board

Being able to test the MPU board on the bench is a great advantage in trouble shooting. A benchtop power supply is quite easy and inexpensive to put together. All that is required is a computer supply and some mods to the connectors. An ATX or old AT computer power supply will supply the + 5 vdc and +12 VDC that is needed to run the first 6 flashes. The 7th and final flash requires +43 vdc and cannot be supplied by the ATX power supply, but the MPU can be "fooled" into thinking it is present. An ordinary ATX computer can be had used or new for under $20. Exact wattage is unimportant. In order to be able to switch the power on and off, the 20 pin connector on a ATX supply must be modded. This is not necessary on an older AT supply. Because modern motherboards use a soft power on/off, the green pwr-ON at pin 14 must be tied to the black COM ground at pin 13 or 15 thru 17. This can be done easily done with a short length of wire and a .062 pin attached to each end and shoved into the 20 pin connector at pin 14 and 15. Or, simply cut the wires free from the connector and solder them together.

Take one of the molex 4 pin connectors which have 1 RED wire (+5 vdc), 1 YELLOW (+12 vdc) and 2 BLACK ground wires. Attach an alligator clip to the RED, YELLOW and one BLACK lead. A good tip is to use the color coded rubber boots to protect from accidental shorts and keep it easier to identify the leads at a glance. If you should accidentally short the +12 volts to +5 via you will kill all the ICs on the board !

To use the power supply, with the power OFF, clip the black lead to TP 4 at the top right of the board. Clip the RED +5 vdc lead to TP 5 at the bottom right, near the battery. Finally clip the YELLOW +12 vdc to TP 2 on the bottom left of the board. Make certain that this connector is not on or shorted to TP3 which is nearby. This error would damage the board, so double check this before turning on the power. Connect the power supply to 120vdc outlet and flip the switch to boot.

Upon power up, you should see the brief flicker, then 6 (not 7) more flashes for a good board. The 7th flash cannot be gotten without +43 vdc present. On some occasions, the LED will lock on and not go into the flash sequence. This COULD BE because the MPU is sensitive to the exact voltage supplied and will not boot with a computer supply, so if it boots in the game, that would be the cause. This condition is rare, but possible. Also, if the LED locks on immediately, try doing a manual reset by briefly shorting together pins 39 and 40 of the U9 CPU with a small screwdriver. This forces the pin 40 to go low and begin the boot process. It is also possible to short the junction of resistors R1 and R3, on the right side of R1, to board GROUND with a jumper clip to accomplish the same effect.

ATX Power Supply connector modification

Bench Top Power Supply hooked up to MPU board

4.3.7 Repairing Alkaline Damage

Should a leaky battery damage your MPU, the first decision to make is this: is the board worth repairing? The extent of the alkaline damage combined with your PCB repair skills, the value you place on your time, and the quality of the result you want to obtain may drive you to replace the board entirely with either an OEM board or one of several aftermarket replacements. Alkaline cleanup, component sourcing and replacement, and socketing troublesome old IC sockets can take 3 to 8 hours.

Should you decide to repair the board, component kits to replace everything in the "corrosion zone" are available from several sources for about $10.

Note: Most alkaline damage repair kits do not include the L1 and L2 inductors which are often damaged. Since these inductors are so small in value, simply replace them with a jumper.

Once you've decided to proceed, to neutralize alkaline, you need an acid. The most common way to accomplish this is to wash the affected area of the board with a mild vinegar solution (50% vinegar to 50% water). Use a toothbrush to scrub the board's affected area and outside the affected area, front and back. After scrubbing, rinse the board with water, then use isopropyl alcohol (the highest percentage you can get - 99% or 91%) in a wave action down the board to displace the water. Let the board air dry, or use a hair dryer without heat to speed the drying process.

After the board is dry, replace any components that were affected by the corrosion damage. The parts will be harder to remove and solder as the combination of corrosion and cleaning makes the solder difficult to heat. Adding new solder before desoldering will help in this process, as will boosting your temperature controlled soldering station up by about 50 degrees. Be careful as the pads are very fragile at this point and can lift easily.

Alternate methods of cleaning the affected areas include bead blasting, and sanding. If the damage is very slight, sanding might work best but you remove all the conformal coating when you do so (that's the green masking material applied to the traces on the board). You have to either replace this coating, or use an alternate material to protect the bare traces from oxidation. Clear nail polish has been used to do this, but isn't a great substitute. You can also tin the affected traces with new solder which will protect the copper. It is also possible to purchase conformal coating but it is toxic and messy to work with.

Bead blasting is a technique that uses small glass beads on a sand-blaster type setup to blast away the corrosion. Again, the conformal coating is removed and should be replaced. Some critics of the bead blasting technique indicate that the corrosion actually gets embedded in the board by this method; however, it is an accepted repair practice in electronics repair. Most people do not have the equipment needed to do this.

Regardless of the method used, any bare copper traces should be at minimum tinned with solder. Often after removing the components, you will need to sand the remaining pad to get a good soldering surface. A small fiberglass sanding pen is ideal for this purpose (available at auto parts stores). It allows precise sanding on small surfaces. Sand right before you solder as copper starts to oxidize immediately. Use a can of compressed air to blow any fiberglass particles out of your work area and be careful using the fiberglass pen as the fibers will become embedded in your skin causing irritation. Wear eye protection as well as you really do not want these particles flying into your eyes!

Use a meter to test your work, following point by point as you replace components to ensure you have a clean circuit path. Add jumpers as needed, and solder replaced components top and bottom to ensure good via continuity. Use a high quality socket when you replace the 5101 ram and be very careful around this area, as it is right next to the battery zone and is usually heavily damaged. All of the traces in this area are part of the address and data bus for all the roms, pias, and cpu, so any shorts or damage here will affect the rest of the board.

Finally, remember also that the alkaline will travel both down and up from the original position of the battery. Inspect the lamp driver board (right below the MPU) to ensure it hasn't become corroded also. If the corrosion was really bad, inspect the J4 connector on the MPU too. Corrosion will travel into the wires in this connector. If this has happened, you must cut the wires back far enough so the corrosion is not seen; otherwise it will leach back into your board and continue to spread through the wiring harness. Hopefully, the harness will still have enough slack to make it to the J4 connector. If not, you can extend the wires neatly by soldering and heat-shrinking new wires onto the harness. Having a parts machine to pull this type of wiring from enables you to match closely the wire markings so prevent confusion in the future.

• Bally/Stern MPU Alkaline Damage Abatement
• 

  The front side of a Stern MPU-200 with alkaline damage removed.
• 

  The back side of a Stern MPU-200 with alkaline damage removed.
• 

  An MPU-200, "corrosion zone" cleaned up.
• 

  A Bally -17 MPU, "corrosion zone" cleaned up.

4.3.8 Using the Dallas/Maxim DS1811 Reset Generator on Bally and Stern MPUs

Like the technique employed to repair alkaline damage on Gottlieb System 80 MPUs, the Dallis/Maxim DS1811 reset generator may be used on Bally and Stern MPUs also. The DS1811-10 has a typical trip point of 4.35VDC. You may also use the Microchip Technology equivalent, part number MCP130-460DI/TO, available from Great Plains Electronics.

Unlike Gottlieb System 80 MPUs, using the DS1811 on Bally and Stern boards doesn't save you much work. It replaces only 10 easily sourced components. And since you've done the hard work of cleaning up the alkaline damage already, using the DS1811 isn't really worth the trouble. But, if you'd like to use the DS1811, the procedure is described below.

After you've cleaned up the alkaline damage, replace all components except these 10:

• VR1
• R1, R2, and R3
• R112
• R138, R139, and R140
• Q1 and Q5

With the board oriented as it would be in the game (J5 at top), install a jumper from the top through-hole of where R139 was, to the bottom through-hole of where R138 was.

There are several ways to form the legs of the DS1811 for a Bally or Stern MPU. However, with the flat side of the DS1811 facing left (i.e. at J4), the legs of the DS1811 should be placed in the prior location of Q5 such that:

• Pin 3 of reset generator (top pin) is where the upper, right lead of where Q5 was
• Pin 2 of reset generator (middle pin) is where the lower, right lead of Q5 was
• Pin 1 of reset generator (bottom pin) is where the left lead of Q5 was

Add a 1K, 1/4W resistor from pin 1 of the reset generator to +5VDC. This signal can be picked up conveniently at the banded end of CR5 (a 1N4148 diode).

• Using the Dallas/Maxim 1811 Reset Generator
• 

  An MPU-200 MPU with alkaline damage abated, and reset components replaced with the DS1811 reset generator.

• 

  The same image, but with the single jumper indicated (yellow dot), where to install the DS1811 flat side facing left, and the added 1K resistor.

• 

  Illustrated picture of components to remove, keep, and jumpers to add.

• 

  Closeup of the DS1811 equivalent installed.

4.4 Solenoid problems

Before proceeding to diagnose solenoid or problems, see this section: How coils are turned on

4.4.1 Replacing a failed Solenoid Transistor

If any coil has locked on, or any SE9302 transistor has failed the diode test with your multimeter, replace the following components on the Solenoid Driver board as a set. In addition, also test the playfield coil disconnected from the game wires, with the ohm setting. The coil should have a value higher than 3 ohms up to around 15 ohms. Lower than 3 ohms is a dead short and will heat up and burn up components if the fuse does not blow. The coil diodes should also be replaced if the coil has locked on. Since the diode must be disconnected from the lugs to test it, it just makes sense to clip it off, replace the diodes, and not bother to test them. 1N4004 diodes or better, (1N4005,6 or 7) should be used. You cannot test the diode in place. The diode band (cathode) goes to the power lug of the coil, usually a double wire connection, because the coils are daisy chained. If it is a single wire, look at another nearby coil and note the color of the double wire.

Replace any suspect SE9302 with a TIP 102 transistor. They are used in many pinball machines, so having a small supply of them is highly recommended. The TIP 102 is a more robust transistor and can handle more current. On the SDB replace the associated diode, and resistor for any driver transistor you replace. Check the associated pin for signs of burning and replace the header pins and connector pins if they have turned brown or look corroded. If a diode and/or resistor has actually burnt, check for continuity and make sure the circuit board traces have not also burnt up. This is a common problem when someone has over-fused the game.

4.4.2 Solenoid Driver Board Transistor, Resistor, Diode & associated Connector Chart

TIP 102	1N4004 Diode	330 ohm Resistor	SDB Connector
Q1	CR1	R9	J1-pin 2, J2-pin 9
Q2	CR2	R6	J1-3, J2-4
Q3	CR3	R16	J2-5, J3-4
Q4	CR4	R18	J1-5
Q5	CR5	R10	J2-10
Q6	CR6	R12	J2-11
Q7	CR7	R14	J2-12
Q8	CR8	R20	J5-10
Q9	CR9	R26	J5-9
Q10	CR10	R28	J5-15
Q11	CR11	R32	J5-14
Q12	CR12	R30	J5-13
Q13	CR13	R22	J5-12
Q14	CR14	R24	J5-11
Q15	CR15	R39	Flipper Relay
Q16	CR16	R34	J2-6, J3-7, J5-8
Q17	CR17	R42	J5-7
Q18	CR18	R45	J2-15, J3-9, J5-3
Q19	CR19	R47	J2-8
TIP 102	1N4004 diode	330 ohm Resistor	SDB Connector

4.5 Lamp problems

Most lamp problems stem from the sockets themselves. The recommended best practice for problem sockets is to replace them. If you want to try and get them working reliably, here are some things you can try:

First off, clean the inside of the socket. There are nice dremel tool tips to help, but even a screw driver can scratch off some crud from inside a socket. Some time a light squeeze on the socket with pliers can make the bulb stay in nice and snug and be less likely to move and stop lighting.

The bare wire running under the playfield for controlled lamp power carries 5-6 vdc and is usually soldered onto the sockets mounting bracket. The mounting bracket then connects to the outside of the socket. After 30 years or so the connection from the mounting bracket to the lamp socket's outside can break. To remedy this there are two things you can try. You can solder the barrel of the lamp socket directly to the base of the socket (so it can no longer swivel). This can be kind of tricky without a higher power soldering iron - if you use paste flux it is easier. Radio Shack also sells a solder called "Crystal Clear" flux which works well. To do this well you need to either sand or file (the file works best and saves your fingers) the area to be soldered on the base and the barrel. The other option is to run a small jumper wire that connects the bare wire directly to the outside of the socket, thus eliminating the poorer connection between the mounting bracket and barrel.

Another less common issue is the connection between the lamp socket's solder lug (insulated wire to the driver board connects here), and the back tip of the socket (what moves out/in and is spring loaded to hold bulb in place). What you can do here is to move the insulated wire off of the lamp socket's solder lug and solder it directly to the back of the socket tip. This eliminates any potential connection issues with the solder lug/tab and the back pin.

Before soldering onto a socket, either the barrel or the spring terminal, it must be sanded or filed clean or the solder will not stick. Paste flux or the crystal clear flux solder recommended above will help. If you have a temperature controlled soldering station crank it up above what you would normally use for boardwork to about 800 degrees.

Another issue is the multiple lamp mounting boards/brackets like those used in Stern Big Game, Meteor, and others. The lamp sockets are riveted to these mounting boards and are not replaceable. These mounting boards suffer from a bad connection to the bare controlled lamp wire running under the playfield. You can either solder each lamp barrel to the base plate or run a daisy chain wire from barrel to barrel to help fix issues with the sockets.

Again, lamp sockets need to be sanded (200 grit works well) or filed before solder will stick. (see picture, below)

If your lamp is always stuck on usually the SCR driving it is bad. Bally/Stern use two different SCR to control lamps. MCR106 is able to drive up to two lamps at the same time. The smaller 2n5060 will only drive one lamp. These SCRs do fail from over sinking of current, from old blackened bulbs (which draw more current) or from being shorted to something under the playfield carrying a high voltage (solenoids). If you accidentally short several lamps together, this would cause the SCR to fail also.

If you are in a bind it is possible to use the more robust MCR106 in place of a 2n5060 with one caveat. Two legs of the MCR106 SCR need to be reversed to be used as a replacement for a 2n5060. As you are looking at the board the top and middle leg of the MCR106 need to be reversed. (see picture, below)

• • note ** a 2n5060 CAN NOT be used instead of a MCR106

Still can't get your controlled lamp to light up and you're sure it's wired up right and getting power? A lamp that never lights might be a bad SCR that needs to be replaced or the connection that runs from the lamp board to the lamp. Use your DMM on continuity test to follow the path from the SCR to the lamp itself to find out if it is a connector issue.

On some lamp boards there are buffer and decoder chips. A bad buffer or decoder chip can prevent a lamp from lighting. If you have multiple lamps out and you have tested the wiring for each, look back to the chips to see if the lamps out have a chip in common. (Refer to the games' schematics) If so, and you have tested the SCR's as good, the chip is probably bad. The .100 headers on the lamp driver boards are subject to a lot of stress and should be resoldered to ensure there are no hairline cracks in the connectors.

All Controlled lamps not working:

Could be rectifier board connectors, bad lamp bridge rectifier, or fuse blown.

Dim controlled lamps:

The biggest cause of dim controlled lamps is a weak connection via the power chain's connectors. The original lamp driver bridge rectifier is slightly undersized on the rectifier board at 8 amps; either changing to #47 bulbs can alleviate some of the load placed on this bridge, or it can be upgraded to a larger capacity (25 amp-up). Changing the header pins on the rectifier board to a 10 amp capable pin plus changing the connector pins will help the power chain. Application of a dielectric to prevent oxidation can help prevent new pins from prematurely wearing out, but do not apply any chemical to old, tarnished pins.

The fuse clips on the rectifier board can get tarnished, too. Replacement with high current phosphor-bronze clips will help dimming issues. The less resistance in the power chain the better and brighter your lamps will be.

4.6 Switch problems

Bally / Stern 5 x 8 Switch Matrix

Bally/Stern games use a switch matrix arranged as a 5x8 matrix for a total capability of 40 switches. Some games (Medusa, Spectrum, and others) have a sixth column of switches making a total of 48 switches in a 6x8 matrix. This guide will concentrate on the "normal" 5x8 matrix but the information applies also to the 6x8 matrix; the sixth column signal wire is merely in a different location, and for switch matrix troubleshooting purposes the information is interchangeable.

Columns 0 and 1 are shared by the playfield and cabinet switches. Any problems with switches in these columns can be further diagnosed by disconnecting the J2 connector (playfield) or J3 connector (cabinet) to isolate the playfield, cabinet, or both from switch tests. Switch test on Bally/Stern machines is entered by pressing the self-test button on the coin door 4 or 5 times, depending on the game. The stock software in each game only shows the lowest switch number that's closed; multiple closures or an entire row/column closed will still only show the lowest switch number. (There is a special test rom available that will walk through all the closed switches one at a time).

Start a switch diagnostic test by removing all balls from a game and placing all drop targets into an upright position. Enter switch test and you should have a zero flashing on the match display, signifying no closed switches. Use the chart from the manual in your game if you see a closed switch to investigate why it's showing closed.

Probable reasons for a stuck switch are:

• points or blades adjusted too closely/touching
• switch diode touching lamps/other wiring
• solder splashes/conductive debris on a switch
• shorted switch capacitor, if used
  

Here is where disconnecting the playfield will help. If you disconnect the switch connector for the playfield from the MPU board (J2) and the stuck switch stays, you know the problem is not on the playfield. If the switch is in column 0 or 1, you might have a problem with the switch matrix going to the cabinet. It is common for switches on the coin door to become mangled, either being stuck closed or shorted to the coin door in some way. You can disconnect the coin door separately while in switch test to see if the switch faults clear.

If you disconnect both J2 and J3 isolating all switches in the game from the MPU board, you should always see the flashing 0 indicating no switches closed in switch test. If you do not, there is a board fault that should be investigated and corrected. All of the signals for pulsing and reading the switch matrix originate and terminate at the U10 6821 PIA chip. As a quick test for this chip, you can swap it with the U11 PIA to see if the problem's symptoms change. If they do or the switch matrix starts to work correctly, you have a probably failed PIA chip and should replace it. Be aware that the U11 PIA chip controls the solenoids in the game, so if the U10 chip is bad in any way, you might have locked on solenoids causing more damage if your fuse doesn't blow. Before swapping the PIA chips, remove the solenoid driver board's .156 connectors to the solenoids to prevent damage. You could also just remove the J4 connector that feeds the solenoid driver board's input signals. (Lower right connector on the SDB).

Sometimes due to wiring error a switch diode is reversed in the switch matrix, either from previous repair work, or even from the factory. When this happens, you will see the wrong switch closing. Test for this by entering switch test and activating each switch one at a time referencing the switch chart in the manual, ensuring that each switch reports the correct switch number. This means that each drop bank will need to be reset by hand after each drop target test. If the game in question has a spinner, test the spinner with the playfield down and then place a piece of paper between its switch points so testing other switches with the playfield up doesn't show a false positive on the spinner from movement.

Momentary contact switches will sometimes have a switch capacitor installed. The purpose of this capacitor is to ensure the MPU board "sees" very quick hits to a tilt, pop bumper, sling, or standup target. Switch capacitors should not be installed on rollover, saucer, spinner, outhole, or trough switches. There are a few games that do have capacitors installed on these switches. You can cut these off safely and not worry about replacing them.

A symptom of a failed (shorted) switch capacitor will be a stuck switch showing in the switch test, and no scoring/scoring once/multiple repeated scoring in gameplay. As a test, you can cut one leg of the capacitor off a suspect switch and see if the problem goes away. If it does, the capacitor was probably bad and you can replace it. (A 0.047 mfd 16 volt or higher non-polarized ceramic disc replacement works well.)

Quick hits to switches that do not have capacitors installed can have a capacitor installed to improve performance, or if you have a pop or sling that activates when hit but does not score. You can add the 0.047 mfd capacitor to these switches on the two lugs that do not have the diode installed; one end of the capacitor goes to the blade lug that has one end of the diode but not the matrix wiring, and the other end of the capacitor goes to the switch lug that only has the matrix wires without the diode. If you do add a capacitor to a sling or pop bumper, be aware that it is possible for radio frequency interference from a coil's collapsing magnetic field to be picked up by the capacitor, causing the switch to activate. This is most common with flipper coils - holding a flipper up and releasing generates a short pulse of radio frequency static.

It is good preventative maintenance on machines that have switch capacitors to methodically replace each and every one with a new one. Adding a switch capacitor to pops and slings is a good idea also as you can run a slightly larger switch gap on the activation switches, which helps to prevent switch bounce and repeat, unwanted, activations.

4.6.1 Leaf Switch Theory,Operation and Adjustment

Leaf switches in pinball games come in 4 formats: Normally Open (N.O.), Normally Closed (N.C.), Break-Make, & Make-Make, the last 2 of which are really combinations of a N.O. and/or a N.C. switch. Regardless of their function, all switches are in fact, a N.O. or N.C. type.

Leaf switches in electronic games are of 2 compositions,at least 2 bronze blades each holding a gold flashed contact or a Tungsten contact. Since gold is a very high conductor of electricity, it is used on most switches, with the exception of the flipper cabinet and End of Stroke (EOS) contacts, which are tungsten. Gold will not tarnish or turn black, but sometimes gets dirty from solenoid dust, and this may effect its conductivity. Tungsten flipper contacts must be redressed with an ignition-type flat file as used in automotive repair, as the contacts are too hard to be smoothed by sandpaper or flex file abrasive. Gold flashed contacts must NEVER be cleaned with a file or sandpaper. A business card, or thin cardboard, is all that is necessary to clean electronic gold flashed contacts. If they seems to have a foreign substance on them, a Q-Tip with a degreaser like Mean Green, or alcohol can be used and then wiped off. Contact cleaner must NOT be sprayed liberally on the switch, but can be applied with a swab.

4.6.2 Normally Open (N.O.) Switch

Normally Open Switch in resting state

Schematic rendering of N.O. & N.C. switches

This is a leaf switch that has 2 contacts that complete a circuit when pushed closed by some mechanical device. The switch re-opens when the device moves away from the moveable contact, and the springiness of the blade opens the circuit.

4.6.3 Normally Closed (N.C.)Switch

Normally Closed (N.C.) switch in resting state with optional nylon spacer

This type of switch opens a circuit when a mechanical device pushes against the blade.

4.6.4 Break-Make switch

Break-Make switch in resting state

This switch is really a composite of a N.O. and a N.C. switch with just three blades instead of four. The moveable center blade has contacts on BOTH sides. Proper adjustment insures that when a device moves the center blade towards the open contact, the CLOSED switch OPENS BEFORE the center contact touches the open switch’s contact. When the pressure is released, the center blade returns to its N.C. side and re-makes contact. This type of switch is often used on relays. A Make-Break switch is really the same, just upside-down, or in reverse, of the order of actions of a Break-Make switch. Special care should be taken with a Make-Break switch that the three blades are at not time shorted together. This can happen often when the blade stiffener is maladjusted, and contacts the other blade of the pair.

4.6.5 Make-Make switch

Make-Make switch in resting state

A make-make switch is a composite switch consisting of two N.O. switches using only 3 blades. When mechanical pressure is applied to the blade, the switch “makes” or closes the circuit, and continues to move until a second switch contact is closed, tying all 3 blades together.

4.6.6 Adjusting Switch Gaps

Proper switch clearance gaps are crucial for correct operation of any pinball game. Very many problems in games come down to a problem with incorrect operation of a switch. The switch blades are made up of phosphor bronze, which has high conductivity, resilience to form and excellent soldering characteristics, but has the drawback of being brittle compared to copper. Switch blades therefore, are commonly broken by the game, or careless actions by the repair person. A switch adjusting tool, purchased or homemade, is a necessity. Pliers or screwdrivers might be used in special circumstances, or in extremis, but are not best practice.

Switches in games are designed to have a degree of over-travel, which creates a wiping motion that helps clean the switch. The contacts must meet, stay together and slide across the face of the contact slightly, to be perfectly adjusted. They also must be gapped wide enough that they do not bounce, causing multiple switch closures. This problem is seen often in electronic games, when the rapid nature of the switch closures cause machine-gunning of the slingshots .

Before adjusting switches, make certain the screws holding the switch stacks are down tightly. Bakelite spacers in the switch stacks, due to excessive moisture, have occasionally shrunk by drying out, causing poor adjustment. After tightening a switch stack, be sure to recheck the gap of each switch.

To adjust a leaf switch, first make sure the switch stack of bakelite or plastic spacers and blades are tightly packed against each other by giving the 2 screws a twist of your screwdriver. As long as there is no screw movement with reasonable pressure, you can procede. Some switches have a regular nut on the backside instead of a speednut, which will require holding it as you turn.

Using your switch adjusting tool, put twisting pressure on the moveable switch blade as close to the switch stack as possible, and include the blade stiffener(if present) in the adjuster slot. Try to use as little force and change of gap as possible, and incrementally reach your gap goal. Using too much force and a back and forth gap readjustment, tends to bend and weaken the switch blade, and can make a deformed switch blade difficult to set for correct operation. This is often seen in games that have been “hacked”, and sometimes the only way to remedy the situation is to replace the entire switch, or disassemble it entirely. Cycle and recycle the mechanical device that activates the switch and observe the switch for proper gap, wiping action and release.

4.6.7 Recommended Gap Specifications

Kicking rubber, or slingshot switches usually have a generous gap, at least 1/16", due to the rubber ring pushing back against the switch, and a bit of trial and error will be necessary to find the ideal gap setting. Pop bumper switches and scoring “dead” bumper switches, should have a gap of 1/64" for the actuating switch under the spoon, and a 1/32" gap for the score switch when open. Flipper cabinet switch have a generous gap which can be adjusted to suit the owner of the machine to provide a good "feel". All other types of switches will probably function well with a 1/32" gap, and this would be a starting point, modifying the gap on a case by case basis.

4.6.8 The Importance of Diodes and Capacitors on Switches

A ceramic capacitor of the type used on switch. NOTE: The number is NOT the correct value for switches. Use 0.047 mfd for replacement

On all Bally and Stern solid-state (SS) pinball games, there MUST be a diode connected to each pair of switch blades. The diode’s purpose is to isolate the switch from the other switches in the switch matrix. A shorted or reversed diode will cause the MPU to read the strobe signal on the wrong return line, causing a switch read error.

Bally (and Stern) used a matrix of 5 columns (strobes, designated 0-4) and 8 rows (returns, designated 0-7) allowing for 40 switches. Some Bally games have a sixth column allowing for 48 total switches. The sixth column games re-use a signal pin from the earlier games that was the sound board address "E" pin. Stern uses this same pin for the 7th digit enable on their displays, and never used it for their sound boards. No Stern game has a sixth column of switches.

You can use a 1N4148, 1N916, or 1N4004 (or better) interchangeably. Bally specifies 1N4148 and Stern 1N4004 as original.

4.6.9 Switch Capacitor Purpose and Failure

Capacitors are used on switches that are normally subjected to very quick hits, to lengthen the switch pulse that the MPU reads. Not all switches will have capacitors; standups, pop bumpers, slings, and tilt mechanisms are the usual ones that benefit from them. All switches that need a quick reaction can have switch capacitors added to them (such as rollover buttons). These are ceramic non-polarized capacitors of a value of .047 or .050 uf and 16 volts or greater. A commonly available cap is the .047 uf 50 volt through Mouser P/N 140-50U5-473M-RC.

The factory installed caps are often damaged by the high wattage industrial soldering irons used in manufacturing the games, or they succumb to the vibration over time and no longer serve their purpose of lengthening the switch closures so the MPU can read them. Often a repairman will clip the cap off to diagnose a stuck switch problem and not bother to replace it. The switch will operate in this fashion, but for more sensitive play, the capacitor should be replaced. A failing cap can also make a switch bounce, and cause machine-gunning of a slingshot or pop bumper.

Sometimes the operation of the flippers or other solenoids will cause a phantom switch close on a pop bumper or slingshot - this is due to the way the software reads the fast react switches on those mechanisms. The RF produced by the flipper coil's collapsing EMF field is picked up by the switch capacitor, causing the pop or sling to fire. In most cases, no score is added, the mechanism just operates. Keeping the leads short on the switch capacitors might reduce their tendency to pick up this stray RF in the machine.

4.6.10 Proper Location of Wiring, Diodes, & Capacitors

Color coded wiring of the playfield switches will vary by game model and manufacturer, but the following should hold true for any Bally or Stern game made from at least 1977 to 1985 . Switches may have two or three lugs, depending on function. If the switch has 3 lugs, one of them is a DEAD LUG, which is electrically isolated from the other switch blades and ground. It may be that the dead lug is off to the side, or positioned the same as the other lug, and it may be difficult to visually verify which is the dead lug. The Dead Lug does not have a blade. The purpose of the dead lug is to have a isolated soldering point for the COLUMN wire(s) and the NON-banded (anode) end of the diode.

Switch capacitor is wired as shown, some switches will not have one.

A stand up target with capacitor & diode

A 3 lug switch will have the following connections.

• A switch capacitor (if required) between the 2 switch blades.
• A ROW wire(s), (with a capacitor leg, if needed) to one end of either switch blade
• A COLUMN wire (usually daisy chained) plus the NON-banded end of the diode to the DEAD LUG
• The BANDED (cathode) end of the diode to the opposing switch blade, either by itself, or sharing the lug with a leg of the capacitor

Remember that switches are usually daisy-chained together, so except for the last switch in a group, there will be a common COLUMN wire (sometimes NOT insulated) between each switch, along with the NON-banded diode. Any break is this wire will cause all the switches below it to not function. Keep in mind that the schematics show a logic progression of switches which may or may not match the physical chain under the playfield. A failed or leaky diode can only be tested for by desoldering one end of the diode & checking with the diode test function of your multimeter. It is very little more work to just simply replace the diode with new if it is suspected.

4.6.11 Troubleshooting multi- ball games that will not start

Bally produced multi-ball games which require ALL balls to be in the correct position before a game will start. If a pinball is stuck on the playfield, missing, or the switch does not register, is broken or maladjusted, then the game will not start. The symptoms each game shows varies. After the game boots, a few insert lights may flash repeatedly, or the game will not coin up, the general illumination will not light and credits will not count down, etc. Check the chart below for specific games.

These switches can be checked in the game diagnostic switch test see if they are stuck closed, or manually operated to see if they register. Remember that only the LOWEST number closed switch will appear on the display, so if other switches are closed or have a fault, they must be cleared to check for the higher switch number.

Game	# of balls	Symptoms	Check switch
Centaur	5	All zeros on; displays flicker	#01 Ball trough 4 #02 Ball trough 5 #08 Outhole (will start with #01 or #02)
Elektra	2	Will not start; displays blank	#01 Outhole #02 Left/Right of Outhole (Starts with #01 or #02)
Embryon	2	Always starts	#05 Left/Right of Outhole #08 Outhole
Fathom	3	Won't start; no GI, 2 insert lights flash, displays blank	#01 Outhole #02 Left of Outhole 1 #03 Left of Outhole 2 (Starts with #1& 2, OR #1&3)
Fireball II	3	Won't start; displays blank	#01 Outhole #02 Left of Outhole #03 Left of Outhole #18 Right of Outhole
Vector	3	Won't start; displays normal	#01 Left of Outhole 2 #02 Left of Outhole 2 #03 Outhole
Xenon	2	Won't start; displays blank	#02 Ball release 1 #28 Ball release 2

4.6.12 Electrical short troubleshooting Fuse helper

Circuit breaker with a blown fuse soldered in position

As an aid to finding the cause for an electrical short, you can make a circuit breaker tool to eliminate the need to constantly replace a fuse, while you investigate the cause. This could save you money in the long run. It is better to under-fuse the connection by a small amount, then to use the rated fuse rating, so a 3 amp circuit breaker could be used on a 5 amp fuse holder, or a 10 amp breaker for a 20 amp G.I. fuse holder. The very small GMA fuses (5x20mm) will probably need some kind of jumper wire setup.

• a burned out fuse of any amperage or voltage (you were saving them just for such a thing!)
• a circuit breaker of 1, 3, 5, or 10 amps, whatever amperage you require for the circuit you are troubleshooting. Buy ones like Mouser P/N 691-CMB10311C3NBA (Carling) or 655-W57-XB7A4A10-10 (Tyco).

Solder the burned out fuse to the spade terminals of the circuit breaker as shown in the photo. Alternatively, make a two wire female spade mini harness, and solder the bare wires to each ends of the bad fuse and attach the circuit breaker that way.

4.7 Display problems

4.7.1 Display High Voltage Section

Bally High Voltage Section Repair

WARNING: This circuit uses high voltages. Don't continue, unless you are confident in your diagnostic abilities.

If all displays are blank, your high voltage (HV) section may not be working. On the Solenoid Driver Board (SDB), use a DMM to measure volts DC on test points TP2 and TP4, to determine if this section needs repair:

TP2 = 150 to 190VDC
TP4 = 230VDC +/- 25VDC

If TP2 is less than about 150VDC or over 200VDC, the HV section is malfunctioning. It is worth mentioning that when the source display voltage rises above the core acceptable levels, the displays will still operate. However, the increased voltage will strain the display circuitry. In turn, the displays glass life expectancy will decrease dramatically. If TP4 is 0VDC, then power is not getting from the Power Supply board, and the problem is located either on the Power Supply, or in the wiring/connectors carrying power to the SDB, so you must correct this before working on the HV section.

Replacing the components in the HV Section
(TP2=0VDC or 230VDC AND TP4=230VDC)
If you prefer to replace only the failed components, follow page 50 of the Bally repair manual, F.O. 560, dtd 20 June 1977.

Since there are not that many components, it is may be less time consuming to replace all the components in the HV section. Most of these components are located between the two large heat sinks. There is a school of thought when working with high voltage regulator circuitry that dictates replacing ALL the components, as a baked, tired, component can take out new components as well. This is one area where shotgunning the section might not be a bad idea.

Check the Parts Suppliers section of the wiki to find suppliers, and get the following replacement parts (1/2 watt resistors can be substituted for 1/4 watt).

Part	Part No.	Location
Transistor	2N3584,250V,2A,NPN	Q21
Transistor	2N3440,250V,1A,NPN	Q22,Q23(heatsink)
Zener diode	1N5275A,140V,1W,5%	VR1
Diode	1N4004,400PIV,1A	CR21
Fuse	3/16A,8AG	F1(-22 only)
Resistor	22k Ohm,1/2W,5%	R51
Resistor	1.2k Ohm,1/4W,5%	R55
Resistor	82k Ohm,1/2W,5%	R56
Resistor	8.2k Ohm,1/4W,5%	R54
Resistor	390 Ohm,1/4W,5%	R52
Resistor	100k Ohm,1W,5%,metal film	R35
Capacitor	0.01 uF, 400V metal polyester	C27,C28
Capacitor	150 uF, 350V (if original, replace)	C26
Potentiometer	25k Ohm, PC-mount	RT1

Remove and replace components

• Clip the old components from the board (make sure you have new ones first).
• Use one of the desoldering methods to remove solder from the holes.
• Stuff board with new components.
• Check for correct orientation on transistors, diodes and the large capacitor if you replace it.
• Leave a little space under components for air flow.
• Bend leads on components so they won't fall out when board is inverted for soldering.
• Double check that all the correct parts are in the correct places and properly oriented.
• Solder the parts to the board
• Clip excess off leads

Ready to test

Prior to powering up and testing, remove all display connectors, or test with F1 removed from the SDB. I recommend connecting your DMM with a clip lead to TP2 prior to powering the game, so you don't have to probe the HV section. Power up the machine and verify TP2 voltage is 150VDC to 190VDC. If the correct voltage is read, power down the machine and reconnect all the displays and put F1 back in. Leave your DMM connected to TP2.

Power up the machine and adjust RT1 so TP2 reads about 150VDC to 160VDC. If some of the displays no longer light, then adjust the voltage up until they are all lit.

New displays may require to be burned in at 190VDC for an hour or two, but then the voltage can be reduced. The lower voltage will prolong the life of the gas plasma displays.

If TP2 is not correct after your repair, you will need to recheck your work. If you cannot find a problem with your repair, then I recommend you follow the troubleshooting steps on page 50 of the Bally repair manual, F.O. 560, dtd 20 June 1977.

After you have repaired your HV section and verified that it is providing the correct voltage, the next part of the wiki will address how to correct problems with the displays.

4.7.2 Repairing Bally/Stern Displays

This page will help you repair your Bally 6- and 7-digit displays. The information is focused on the AS-2518-21 display. Since the AS-2518-15 display is interchangeable with the "-21" display, everything mentioned here will apply to both displays. Bally 7-digit displays (AS-2518-58) work the same way, they just contain additional components to support the additional digit, and lighting of commas. Some Stern DA-100 6-digit displays are very similar to the Bally versions, and the information here will also work for them. The Stern 7-digit display is slightly different, as its circuit board is physically deeper than any of the other displays and is not directly interchangeable with a Bally 7 digit display. Additionally, there are some input pin differences; however, if you have the schematic you can use the information here on the display, some transistors might be labeled differently.

First off, let's make sure your malfunctioning display is even repairable. If the glass display itself is shot, there's not much that can be done except to replace it. Here's a couple of photos of things that can go wrong with the glass display.

Burn spots on the digit segments - You can't fix these but you can live with them

Broken glass nipple - This display glass is ruined

Then there's the circuit board. Most if not all of the components can be replaced without much effort, but if there is damage to the circuit board itself, it may be impossible, or unreliable to repair.

Burn marks on the driver board

Underneath - The traces are a mess

So we're assuming you have displays that do not fall into the categories above. If your problem is with the digits not being displayed properly, and it's NOT the MPU's fault, then it can be fixed, and fairly easily too!

FIRST THING - Before you go any further, there are two things you should do to ALL your displays, even if they seem to be working fine. First, reflow the solder on the joints for the header pins. On the bottom side of the circuit board, just heat each header pin solder joint with your soldering iron, then add a little fresh solder. Be careful not to create any solder bridges between adjoining pins, unless there is already one there. Next, replace the six 100K ohm 1/4 watt resistors with 1/2 watters. They are the ones with the color code brown-black-yellow, and are labeled R1, R3, R5, R7, R9 and R11. You'll find seven of them, but only the ones I just listed need to be replaced. For 7-digit displays there will be eight of them, so replace R56 too, along with the six I just mentioned. 1/4 watt is just too small for their circuits and often they are overheated which causes them to change their resistance. On the photo of the burnt circuit board up above, the area that was burnt was under 3 of these resistors.

SECOND THING - Connectors, connectors, connectors! There are lots of signals going from the MPU to each display driver, and if these signals are not making it due to bad wiring or connectors, then your displays will misbehave. Check all the display driver connectors for loose or broken wires, burnt pins, busted connectors, and replace or repair anything that looks bad. Remember that some of the signals are daisy-chained from display to display, and a bad connection at one display can effect the others "downstream". Then check the J2 connector on the MPU, since this is where all the signals come from. Next check the J3 connector on the solenoid driver board. There's a high voltage regulator used by the displays on this board, and J3 is where it gets the 230 VDC from the power supply (pins 6 & 3) and feeds the regulated 190 VDC to the displays (pin 8). Finally, check the J3 connector on the rectifier board, since this is where the high voltage comes from. Connectors are always a big pain!

Header pin solder joints - Notice the cracks around the last two pins on the right

Header pin solder joints after being re-soldered - No cracks

Can you find the six 100K ohm resistors (brown-black-yellow)

Here they've been replaced them with 1/2 watt resistors of the same value (100K ohms)

Now we'll look at come common problems and briefly describe the cause, but I assume you've already replaced or checked the 100K Ohm resistors and re-soldered the header pins:

All displays are blank

Most likely cause of all blank displays is a lack of high voltage. First off, check F2 on the rectifier board. It's a 3/4 Amp slow blow fuse and it's test point on the rectifier board is TP2. You should read 230 VDC at this test point. If it's OK, then check the fuse on the solenoid driver board. The high voltage regulator's output is fused and if this fuse is blown then there's probably a short somewhere on one of your displays or the wiring harness. The high voltage regulator fuse is a 3/16 Amp, but it's a bit smaller (8AG) than a standard fuse, and a hard one to find. If the fuse is not blown, then the next thing to do is verify that at least 170 VDC is making it from the regulator to the displays. Check TP2 on the solenoid driver board. It should read between 170 and 190 VDC. If it does, then the regulator is working. While you're there, if your display glasses are not new, use the small trimmer pot on near the fuse and adjust the high voltage to be 170 VDC. Older displays work just fine on 170 VDC and it's less stressful.

Next thing to check is to be sure that the 170 volts is making it to the displays. Check connector pin J3-8 on the solenoid driver board, that's where the 170 VDC leaves. Check for a good connector, and check the solder joint on the header pin. The high voltage hits all of the displays at connector J1-1 and is daisy-chained from display to display. Check these connectors and the header pins too. On at least some early Stern games like Dracula, there is a fuse for the displays mounted on the back of the backbox door, often covered by a cardboard tag. It may be that these early games came without the fuse on the SDB. Check for proper amperage and continuity on this fuse holder if no voltage is reaching the displays.

Note - If there is any light at all on the display, then it is probably repairable. Some type of Bally display glasses will have some light on them, besides the digits. If there is light anywhere on the display, then the glass is most likely OK and your problems are elsewhere.

See how this display is glowing when it's first turned on? This indicates that the glass is good.

.

REMEMBER - 170 VDC WILL HURT!
TURN YOUR MACHINE OFF IF YOU'RE GOING TO MESS WITH IT BEYOND MEASURING VOLTAGES

If you have 170 VDC at all of the displays, and the decoder is still working, but the displays are still blank, then there is probably a problem on the MPU or the MPU connectors, such as a "stuck-on" blanking signal, etc.

If the blanking signal for the displays is stuck high or low on the MPU then the displays will remain blank. To check the blanking signal use your DMM or logic probe on MPU J1 P10. During the flash tests it should remain high (5v on DMM). Once attract mode begins it should begin pulsing (DMM will show somewhere between 1v and 4v). If the blanking signal is stuck high or low examine the blanking circuit including CR6, U14, U20. It could be the PIAs but unlikely as the power on flash test should check that the PIAs changes states. I have seen CR6 be open and cause displays to be blank.

A single display is blank

If you have one display that is blank, it could be the same problems as mentioned above (lack of 170VDC), something wrong on the circuit board, or something with the glass display itself. If you see any light glowing at all on the display, then the glass is most likely good and your problem is elsewhere.

The main cause of a single display being blank is a bad glass. If the glass is good, then your problem is most likely a bad 4543 decoder IC. The decoder on the display driver board is used to decode the digit data from the MPU into signals that light the proper displays. If the decoder is blown, then this could cause the display to be blank. A quick check with a logic probe will help you decide if the decoder is function properly.

Sometimes the solder joints on the display glass needs are cracked and need to be reflowed. Depending on which solder joints are bad, this could cause the display to be blank.

If you can verify there is 170VDc, and the decoder is working, then it may be just a bad display. If there is some light anywhere, then it's probably good. If not, it may or may not be good. A totally blank display is the hardest thing to fix. If everything looks good, but the display is completely blank, then you may just have to chalk it up as a bad display glass. Unfortunately they can not be repaired.

All displays are missing the same digit

If all the displays have the same digit out, then the problem is most likely caused by a bad connector at the MPU. The MPU daisy-chains the digit enable signal to all the displays, and if the same digit is out on all, then it's either an amazing thing that they all have a problem w/ the same digit, or the digit enable signal is not present. Check the connectors on the MPU and all of the displays. If all seem well, then one-by-one, disconnect each display and see if the problem goes away. If it does, then there's a short or a bad connector problem on the board you just removed. Be sure to turn the power off between swap-outs, and wait 10 seconds for the high voltage filter capacitor to discharge before you remove any connectors.

One display is missing the same segments on all the digits

Each display has it's own decoder chip, which takes four inputs from the MPU and outputs seven signals to light the seven segments of a digit. If you're having problems with one or more segments on all the digits, then it's either the segment driver transistor or the decoder itself. I'm sure there's a way to test the transistor but I just go ahead and install a new one. If that doesn't fix it, then replacing the decoder will. I've not had a segment problem that was not fixed by replacing both segment drivers and decoders (other than MPU problems). Be sure to orient the transistor and/or IC in the proper position. You'll notice a flat side on the transistor and a small notch on one end of the decoder IC. Be sure they line up just like the one you removed, and that the wires of the transistor go into the same holes that the old one came out of. Also, if you're replacing the IC, use a socket, so it'll be easier to replace it next time. Here's a handy chart that shows which segment driver transistor drives which segment, and another diagram of how the segments are labeled. Just find the segment that's giving you trouble on the chart, then look up it's corresponding driver transistor. Then find this transistor on the circuit board and replace it.

One digit is out on one of the displays

If you have a single digit out, then it's probably the the level shifter and digit driver transistors for that digit. Just to be sure, check the connector on the display at pins J1-4 through J1-9. These are the connectors that supply the digit-enable signals from the MPU. Your problem may be that the display driver is not getting the enable signal from the MPU. If it is, then just replace the two transistors and you should be back in business. Here's a handy chart that shows you which level shifter and digit driver are associated with each digit. You'll find the transistor labels printed on the circuit board, or look at the diagram below. Just look at this chart, find the digit that's blank, and then locate the two transistors listed for that digit. Find them on the circuit board and replace them.

One digit is very bright, and the rest are out

If you have one digit that's very bright and all the rest are out, simply replace the digit driver and level shifter transistors for that digit. Turns out sometimes a short transistor will draw so much current that there's not enough left to drive the remaining digits, and so they all go blank. Just use the chart above to determine which transistors to replace.

Display(s) flicker

Closeup of Cracked Header Pins on a Bally/Stern Display Module. These cracks caused rapid "flicker" of the display.

This is almost always caused by broken solder joints on the header pins. If you already re-flowed the solder, double check them, then look for other broken solder joints and check all connectors for tight fits. Something is loose that's making them flicker.

Another cause of flickering or strobing digits is a faulty decoder IC. If your digits are flickering or "wavy", try replacing the decoder IC.

Here is a link to a video of a display board with a faulty 4543 decoder IC. Keep in mind that failed / failing decoder chips do emit symptoms other than what is seen in the video. Please see the other symptoms discussed above in this section.

Conclusion

That covers the most popular problems. I hope it covers yours. If you don't have the manual for your pinball machine, click on any of the thumbnails below for a large picture of the component layout of the all three boards. The 100K Ohm resistors are the ones colored brown-black-yellow.

4.7.2.1 Display Examples

Here are the 3 types of Bally displays:

AS-2518-21 6-Digit Display

AS-2518-15 6-Digit Display

AS-2518-58 7-Digit Display

Here is the Stern DA-300 display. Note that the circuit board is deeper than any of the other display types.

4.8 Sound problems

Regardless of the sound board, it is always best to first remove the existing solder from the header pins, and reflow new solder onto them. Due to vibration over time, the header pin connections can end up with cracked solder joints, which is very common on the Bally sound boards. The next order of business would to replace the volume pot and the secondary pot, if one is used on the board. The original, factory pots used were not sealed, therefore, dirt and other contaminants can cause the pot to have dead spots or fail in general. Once these two things are done initially, troubleshooting the sound board, if it's still not working will be a lot easier.

If the board is still not working after the above recommended procedures, the next thing would be to check all of the voltages used on the board. See the Sound Test Point Value section for the test point voltage values for each particular sound board.

If all of the voltages check out, it's time to move onto the appropriate sound board troubleshooting section below.

4.8.1 -32 & -50 Sound Board Troubleshooting

Both the -32 and -50 sound boards use at least two 10Kohm pots. One for volume and the other for sustain.

Should the 86L93 (U11) chip fail, the 74LS93 is a viable substitute.

A bad 1N4004 diode (CR3) on the incoming 43V line can cause the CPU to halt at 6 flashes upon boot up.

4.8.2 -51 Sound Board Troubleshooting

The lack of an on-board test LED makes this board a bit difficult to troubleshoot. Fortunately, all of the big ICs on this board are socketed. Like all sound boards of this age, the capacitors are likely to have dried out and no longer work. Capacitor kits for this board can be found at Great Plains Electronics.

If the board is producing no sound at all, start by checking the volume adjustment pot. When you turn the pot you should hear the volume of the hum go up and down. If you do not hear this the amp/pot may be bad. If you hear the hum volume change then it is likely that the amp and pot are working. However, the 1K volume adjustment pot is 30+ years old and was an "open" design. It is recommended that this pot be replaced with a quality sealed 1K ohm pot.

Check the power at the board with a DMM. TP3 is ground. TP2 and TP1 should measure 5VDC and 12VDC respectively. These are nominal values. Minor variation from these values is acceptable.

Next it is time to check the large ICs on the board itself. First, swap the 6821 PIA at U2 on the sound board with either U10 or U11 on the MPU and retest. Second, swap the 6810 RAM at U10 on the sound board with the 6810 at U7 on the MPU and retest.

If the problem persists, swap in a known good sound ROM at U4 and retest.

If you have a known good 6808 (a 6802 can be used with the proper jumpers), swap it for the processor at U3 and retest.

If you have a known good AY-3-8910, swap it for the sound IC at U1 and retest.

You can also check the sound interrupt signal and the sound select signal IC. Connect a logic probe to the board; red lead at TP2, black lead at TP3. With J1 connected to the game and your probe on pin 40 of the PIA at U2, the signal should start high. When the MPU completes it's 7th flash, it will command the sound board to make the boot sound, pin 40 will go low for a split second, then return to high. If all goes well, consider the sound interrupt signal good.

Test the function of the sound select inverter IC at U5. U5 is a simple hex inverter. In attract mode, with no sounds being produced, pin 3 should be low, pin 2 should be high. Pins 5/4, 7/6, and 14/15 should test the same as pins 3/2. Pins 9 and 11 may not be connected on your game. If so, there will be no signal on those pins. However, their "inverted" signals at pins 10 and 12 should be high. Pins 13 and 16 not connected.

4.8.3 Sounds Plus Sound Board Troubleshooting

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4.8.4 Vocalizer Speech Board Troubleshooting

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4.8.5 Squawk & Talk Sound Board Troubleshooting

All of the versions of Squawk & Talk sound boards use two 1Kohm pots. One is used for volume control, while the other is for speech.

4.8.6 Say It Again Reverb Board Troubleshooting

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4.8.7 Cheap Squeak Sound Board Troubleshooting

The Cheap Squeak's LED should flash four times for a successful boot up sequence. Two quick flashes, a pause, two more quick flashes then stay on. Once the LED stays on, it seems to turn itself off for certain sounds, and then turn back on. Likewise, it appears to idle with the LED on, when no sounds are playing.

4.8.8 SB-100 Sound Board

Technical write up regarding the SB-100 sound board is located here.

4.8.8.1 Adjusting the Sound Quality on a Stern SB-100 board

Earlier versions of the Stern SB-100 Sound board can have an unpleasant high pitched sound for all the different sounds. STERN advises the following changes to lower the frequency of the tones, which sound much better to my ears.

• replace all 3 of the 5k potentiometers at R2,R6, & R13 to 25k ohm pots. Suggested part # is 15mm Piher PT15LH06-253A2020
• Replace the 2.2k ohm resistor at R12 with 8.2k 1/4 watt
• adjust the frequencies by putting the RED lead from your multimeter set to the Frequency (Hz) setting, on the TP and the BLACK lead on a ground on the sound board and turning the pots one way or the other in small increments to the following specs.

• TP2 Adjust R6 138 Hz +/- 3Hz
• TP3 Adjust R2 104 Hz +/- 3 Hz
• TP5 Adjust R13 172 Hz +/- 3 Hz

4.8.9 SB-300 Sound Board

Technical write up regarding the SB-300 sound board is located here.

4.8.9.1 Stern SB-300 Sound Board Modification for VSU-100 Usage

Games with a VSU-100 speech card require a modified SB-300 to utilize the speech. First, see if your SB-300 already has a trace for this connection by checking continuity between pin 5 of the rightmost connector at the bottom and the top of capacitor C14. If you read continuity, you do not need to do this mod.

• Stern SB-300 Added Jumper Modification for Speech
• 

  First solder point for jumper
  (pin 5 of rightmost connector)
• 

  Second solder point for jumper
  (top of capacitor C14)
• 

  Overall picture of jumper

4.8.10 VSU-100 Speech Board

Work in progress.

Pray the S14001A speech chip isn't bad on this board!! Really hard to find.

4.9 Flipper problems

4.9.1 Photo Identification of Different Types of Flipper Assemblies

• Bally & Stern Flipper Assemblies
• 

  Early Bally Flipper mechanism from a 1978 Star Trek
• 

  Later Bally Flipper mechanism from a 1981 Medusa. Commonly referred to as "linear flippers". Note-Double EOS switch for Upper Zipper Flipper
• 

  Early Stern Flipper mechanism from a 1979 Dracula. Note-Double EOS switch for Upper Flipper
• 

  Later Stern Flipper mechanism from a 1981 Star Gazer

4.9.1.1 Rebuilding Flippers

Nothing makes more of a difference on a game than having taut, crisp, flippers. Even if every other mechanical component on a game is rebuilt, if the flippers are sluggish and weak, players walk away with a sour taste of the games' experience. At a minimum, flippers should be taken apart, inspected for wear, have their coil sleeve replaced with new, and reassembled while dressing any worn plungers/stops with a file. Additionally, the end of stroke switch should be filed and adjusted, as well as the cabinet switches that actuate the flippers.

It is best to replace the plungers and links, the coil stop, and the end of stroke switch(es) with brand new components. Quality varies in replacement parts for this era game, with some components being completely unavailable in suitable replacements. One example is the proper Stern coil stop for flippers - while there is a modern replacement, it is very expensive and does not seem to work as well as the original copper colored stops. You can swap the copper stops from stern pop bumpers which show very little wear into the flipper positions. The worn stop from the flipper will usually work on the pop bumper fine as the pulse rarely pulls the pop plunger down to the stop (hence why they are perfect to swap).

When reassembling the flipper, check the bushing for cracks or wear - the bushing's job is to hold the flipper bat square to the playfield at a high enough height to prevent the flipper from dragging across the playfield surface, causing gouging and wear. Be sure the flipper has a slight up-down leeway built in at both rest and at extension. The inlane guide should be a smooth transition from guide to flipper; while you can't adjust the flipper to tweak this, you can and should adjust the lane guide.

{WIP}

4.10 Setting Free Play

If you read the manual that came with your game, you'll notice there are no factory provisions for setting the games on non-coin play. There are several options for homeowners to set their machines up so quarters or opening the coin door aren't required.

Free play via low replay scores

The easiest way to keep a quantity of credits on the machine is to set the first replay score to a very low value (10,000 on most machines). This way you can put several credits on the machine initially, and then each game played will probably win a credit. Press the self-test button inside the coin door until you see "01" in the ball-in-play display. Press the button on the mpu board itself (S33) to clear this value to zero, then use the credit button (on the coin door) to step the setting one click forward to 10,000. (Some games let you 'flick' a coin door switch to zero the value, S33 works for all games)

In most cases you will score 10,000 very quickly enabling the machine to self-replenish its credits.

Free play via adding a switch

If you like having the 'coin-up' sound most machines make, adding a free play switch to a game is relatively simple. Any type of normally open switch can be soldered to one of the coin switches and mounted in an unobtrusive way (through the coin door return is a popular example, or mounted to the coin return instead). While it is also possible to drill a hole in the cabinet or coin door to mount this type of switch, it is discouraged to do this as it is difficult or impossible to reverse cleanly.

This type of switch can be piggybacked onto the credit button switch itself, the initial full press will add a credit, and the pullback stroke will start a game.

Free play via ROM replacement

As of this writing, free play replacement ROMS are available for all Bally/Stern games. For many years only Bally freeplay roms of various flavors were available, and these romsets are incorporated into some of the aftermarket replacement MPU boards. In 2009 freeplay roms became available for all the stern mpu-100 and mpu-200 games as well, but as of yet (5/2011) are not incorporated into any aftermarket boards.

Some varieties of free play roms never let the credits go below one, some require a DIP switch setting, and some are free play only. Regardless of the type of free play rom used, they all work similarly. When the credits fall below a certain amount, the software code either increments a credit automatically, simply allows a game start with credits showing 00, or never let the credits decrement below 01.

For many people free play roms are the preferred method of handling free play as no hardware modifications are needed to incorporate free play, and you can still have replay levels set to challenging levels. It also allows the machines to be placed in clubs, businesses, shows, etc. without the owner having to worry about people not knowing how to add credits via some other method. Press the credit button and go.

5 Game Specific Problems and Fixes

5.1 Stern Seawitch

Problem:The ball gets trapped between the glass and the left side plastic above the 3 drop targets, from a hard shot to the center 3 drop targets.

Solution: Cut a 11" (28cm) long by 5/8" to 7/8" (16mm to 22mm) strip of acrylic commonly used for home window glass replacement. Acrylic sheet can be scored and cut with a knife, but a bandsaw works best. Remove the plastic protector sheet, and plan the areas and angle you wish to bend.

With a propane torch (the instant on Benzomatic is great for this), heat the bend area for 2 seconds, and form the bend freehand or with a tabletop. The acrylic will stay soft and bendable for about 20 seconds, so if the angle is not right you can change the bend with or without additional heat from the torch. Clean up the cut edges and corners with a file and/or sandpaper. Brackets can be made out of thin stainless or mild steel. Keystone makes a bracket that is small and has 1 hole tapped for a 6-32 screw. (Manufacturer P/N#614 or Mouser P/N 534-614) A 6-32 nut & 3/8" computer case screw can be used to provide the needed clearance.

Ball deflector installed on a Seawitch

5.2 Bally/Stern LED stays on after boot

7th flash produced but no led dimming afterward: The problem was one of the capacitors around the u12 (clock signal) was bad. I replaced c12,c16?, and c17. After that I got the 7th flash and the dimmed led afterward

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5.3 Solenoid expander board

There is a 555 bulb near (or sometimes not so near) that lights when the solenoid expander is activated. This bulb is essential for proper operation of the expander as the main opto isolator chip on the expander board needs a load to work; if you're having entire sets of solenoids not working, check this bulb.

The header pins on this board like to crack, also, so standard operating procedure should be to replace or at minimum resolder the headers, and re-pin the connector with Trifurcon connectors.

Also, it's very important that all solenoids on the expanded circuits have *TWO* diodes on them! If you or someone in the past replaced the coils with one that one had one, multiple solenoids will activate on any solenoid expanded solenoid, causing a memory drop to activate when it shouldn't, or a target bank reset when a saucer ejects.

Bally Solenoid Expander board- Arrow indicates necessary bulb

5.4 Using a Bally 7 digit display in a Stern game or using a Stern 7 digit display in a Bally game

Bally and Stern 7 digit displays are interchangeable. However, Stern displays do not support commas and a small modification to the printed circuit board is necessary to make each board display all 7 digits in a "foreign" platform.

First, use a small jumper to connect J1, pins 11 and 12 together. Bally and Stern chose different pins to strobe the 7th digit. Without this mod, placing a Stern 7 digit display into a Bally game will result in the 7th digit not being displayed (and vice versa). Making this modification creates a "universal" Bally/Stern 7 digit display.

Bally and Stern also chose a different depth dimension for their display PCBs. Fortunately, the difference can be accommodated merely by mounting the display tray on the opposite side of the lamp insert panel. Note that this is also necessary when using "PinScore" displays in a Stern game. Alternatively, if using a Bally (or PinScore) display in a Stern game, since the Bally circuit board itself is not as deep, insert the display only as far as necessary for it to "flush up" to the backglass when installed.

Bally displays automatically show commas whenever the thousands and millions digits are lit. To make a Bally display "match" the Stern display's non-comma capable display, clip the base lead from Q22 and commas will no longer light up. You can alternatively clip one end of diodes CR1 and CR2 and lift the diodes off the board. This modification would be easier to reverse.

Since Stern 7 digit displays do not support commas, using a Stern display in a Bally game will look a little "off" versus the other displays in the game, but this will get your displays running if you have no other choice.

5.5 Bally Game running slow(delayed score, controlled lamp flicker) or if game crashes before attract mode starts

If you bally game is running very slow(solenoid pulses are delayed and long, controlled lamps flicker, scoring takes a few seconds to register) or if your games boots and flashes 7 times but crashes(dead game with junk on the displays) before attract mode starts you may have a bad C16 cap. C16 cap controls the display interrupt speed. If it is out of spec it could cause display interrupts to be too quick and bog down the processor. C16 cap is in the corrosion area along with the 555 timer.

See youtube video of slow game caused by c16 cap. http://www.youtube.com/watch?v=TlGMGLHrDD8&feature=channel_video_title

5.6 Converting a Bally -17, -35 or Stern -100 CPU Board to a Stern -200

Stern MPU-200 CPU boards are probably the least common of the four CPU boards. The -200 boards are compatible in -17, -35, and -100 games. Although considering that -17, -35, and -100 boards are much more prevalent, it would be somewhat of a waste to use a -200 in any of these games. What if the more common boards could be converted to a -200? Check out WarpZoneArcade's blog entry to find out how to modify a -17, -35, or -100 to work as a -200.