Bally/Stern

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1 Introduction

Bally -17 Board Set

Bally -35 Board Set

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.

For an interesting read, the patent Bally filed for their first "computerized pinball machine" can be viewed here.

Placeholder for Stern M-100 Board Set

Stern M-200 Board Set

The early circuit boards were fabricated by a company called Universal Research Laboratories (URL). URL was purchased by Gary 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.

Bally Goldball special driver/voltage board

Some later -35 Bally games used a combination of the solenoid driver board and the lamp driver board.

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

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	Additional Boards	Transformer
Freedom	AS-2518-17	AS-2518-18	AS-2518-14	Chimes		E-122-125 ^{see note}
Night Rider	AS-2518-17	AS-2518-18	AS-2518-14	Chimes		E-122-125
Black Jack	AS-2518-17	AS-2518-18	AS-2518-14	Chimes		E-122-125
Evel Knievel	AS-2518-17	AS-2518-18	AS-2518-14	Chimes		E-122-125
Eight Ball	AS-2518-17	AS-2518-18	AS-2518-14	Chimes		E-122-125
Power Play	AS-2518-17	AS-2518-18	AS-2518-14	Chimes		E-122-125
Mata Hari	AS-2518-17	AS-2518-18	AS-2518-23	Chimes		E-122-125
Strikes & Spares	AS-2518-17	AS-2518-18	AS-2518-23	Chimes		E-122-125
Lost World	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32		E-122-125
The Six Million Dollar Man	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32		E-122-125
Playboy	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32		E-122-125
Voltan	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32	A few games were outfitted with an AS-2518-51 sound board for testing	E-122-125
Supersonic	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-32		E-122-125
Star Trek	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50		E-122-125
Game Title	MPU	Power Supply	Lamp driver	Sound	Additional Boards	Transformer
Paragon	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50		E-122-125
Harlem Globetrotters	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50		E-122-125
Dolly Parton	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-50		E-122-125
Kiss	AS-2518-35	AS-2518-49	AS-2518-23	AS-2518-50	Auxiliary Lamp Driver AS-2518-43	E-122-131
Future Spa	AS-2518-35	AS-2518-49	AS-2518-23	AS-2518-51	Auxiliary Lamp Driver AS-2518-43	E-122-131
Space Invaders	AS-2518-35	AS-2518-49	AS-2518-23	AS-2518-51	Auxiliary Lamp Driver AS-2518-52	E-122-131
Nitro Groundshaker	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-125
Silverball Mania	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-125
Rolling Stones	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-125
Mystic	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-125
Hotdoggin	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-125
Viking	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-125
Skateball	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-131
Frontier	AS-2518-35	AS-2518-18	AS-2518-23	AS-2518-51		E-122-131
Xenon	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-56 (Sounds Plus)	Auxiliary Lamp Driver AS-2518-52, Vocalizer module AS-2518-57	E-122-142
Game Title	MPU	Power Supply	Lamp driver	Sound	Additional Boards	Transformer
Flash Gordon	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61 (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, early games used the AS-2518-56 sound board and Vocalizer module AS-2518-57	E-122-142
Eight Ball Deluxe	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, Solenoid Expander AS-2518-66	E-122-142
Fireball II	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, Auxiliary Driver - SCR Lamp Flasher AS-2518-67, Auxiliary Driver - GI Flasher AS-2518-68	E-122-142
Embryon	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52	E-122-142
Fathom	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, Solenoid Expander AS-2518-66	E-122-142
Medusa	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61A (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52	E-122-142
Centaur	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B (Squawk & Talk)	Say It Again AS-2518-81 (Reverb), Auxiliary Lamp Driver AS-2518-43, Solenoid Expander AS-2518-66, Auxiliary Driver - SCR Lamp Flasher AS-2518-67, Auxiliary Driver - GI Flasher AS-2518-68	E-122-142
Elektra	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, Solenoid Expander AS-2518-66, Auxiliary Driver - GI Flasher AS-2518-68	E-122-142
Vector	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, Solenoid Expander AS-2518-66, Auxiliary Driver - GI Flasher AS-2518-68, Auxiliary Driver - Triac Lamp Flasher AS-2518-82	E-122-142
Spectrum	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B (Squawk & Talk)	Uses a second AS-2518-23 for lamps (2 total in game), Auxiliary Driver - SCR Lamp Flasher AS-2518-67, Auxiliary Driver - GI Flasher AS-2518-68	E-122-142
Speakeasy	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-51	Auxiliary Lamp Driver AS-2518-52, Solenoid Expander AS-2518-66	E-122-142
Rapid Fire	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B (Squawk & Talk)	Ball Delivery Sensor & Motor Board AS-2518-102	E-122-142
Granny and the Gators	AS-2518-133	AS-2518-132	AS-2518-107 (combo lamp and solenoid driver)		Vidiot Deluxe AS-2518-121	AS-3071-12
Mr. & Mrs. Pacman	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, Solenoid Expander AS-2518-66, Auxiliary Driver - GI Flasher AS-2518-68	E-122-161
Baby Pac-Man	AS-2518-133	AS-2518-132	AS-2518-107 (combo lamp and solenoid driver)		Vidiot AS-2518-121	AS-3071-12
Eight Ball Deluxe Limited Edition	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61 (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52, Solenoid Expander AS-2518-66
Game Title	MPU	Power Supply	Lamp driver	Sound	Additional Boards	Transformer
BMX	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-51	Solenoid Expander AS-2518-66	E-122-161
Centaur II	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61B (Squawk & Talk)	Say It Again AS-2518-81 (Reverb), Auxiliary Lamp Driver AS-2518-43, Solenoid Expander AS-2518-66, Auxiliary Driver - GI Flasher AS-2518-68	E-122-142
Goldball	AS-2518-133	AS-2518-151	AS-2518-147 (combo lamp and solenoid driver)	AS-2518-51	AS-2518-68 GI Flasher	E-122-170
Grand Slam	AS-2518-133	AS-2518-151	AS-2518-147 (combo lamp driver/solenoid driver/regulator)	AS-2518-51		?
X's & O's	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045 / A080-91603-B000 (Cheap Squeak)		E-122-142
Kings of Steel	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045 / A080-91603-B000 (Cheap Squeak)		E-122-142
Black Pyramid	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045 (Cheap Squeak)	A084-91614-A000 Aux. Lamp Driver	E-122-142
Eight Ball Deluxe Classic	AS-2518-35	AS-2518-54	AS-2518-23	AS-2518-61 (Squawk & Talk)	Auxiliary Lamp Driver AS-2518-52	?
Spy Hunter	AS-2518-35	AS-2518-54	AS-2518-23	M-051-00114-B045 (Cheap Squeak)		E-122-142
Fireball Classic	AS-2518-35 †	AS-2518-54	AS-2518-23	M-051-00114-B045 (Cheap Squeak)		AA40-0037-0000
Cybernaut	AS-2518-35 ‡	AS-2518-54	AS-2518-23	M-051-00114-B045 (Cheap Squeak)		?

*Note: Part of the AS-2877 POWER TRANSFORMER MODULE which has the AS-2518-18 Rectifier Board Assembly mounted directly onto the transformer using a bracket. Later games had the AS-2877-1 POWER TRANSFORMER MODULE which had a large metal plate onto which both the transformer and AS-2518-18 Rectifier Board Assembly were mounted. See Inside Backbox photo on the Internet Pinball Database page of Freedom for an example of AS-2877. See also Page 4 of the Bally 1979 Parts Catalog.

† Note: Fireball Classic was sometimes fitted with a 6802 MPU board (an upgrade from the -35 board)

‡ Note: Cybernaut was sometimes fitted with a 6802 MPU board (an upgrade from the -35 board), or a 6803 MPU board.

2.2 Stern

Game Title	MPU	Power Supply	Lamp driver	Sound	Notes
Pinball	M-100	TA-100		Chimes
Stingray	M-100	TA-100		Chimes
Stars	M-100	TA-100		Chimes
Memory Lane	M-100	TA-100		Chimes
Lectronamo	M-100	TA-100		SB-100
Wild Fyre	M-100	TA-100		SB-100
Nugent	M-100	TA-100		SB-100
Dracula	M-100	TA-100		SB-100
Trident	M-100	TA-100		SB-100
Hot Hand	M-100	TA-100		SB-100
Magic	M-100	TA-100		SB-100
Cosmic Princess	M-100	TA-100		SB-100
Meteor	M-200	TA-100		SB-300
Galaxy	M-200	TA-100		SB-300	Uses relay to turn on / off general illumination
Ali	M-200	TA-100		SB-300	Uses relay to turn on / off general illumination
Game Title	MPU	Power Supply	Lamp driver	Sound	Notes
Big Game	M-200	TA-100		SB-300	First Stern 7 digit game, widebody
Seawitch	M-200	TA-100		SB-300
Cheetah	M-200	TA-100		SB-300	First stern game using plastic pop bumper rod and ring, widebody
Quicksilver	M-200	TA-100		SB-300
Stargazer	M-200	TA-100		SB-300
Nine Ball	M-200	TA-100		SB-300
Iron Maiden	M-200	TA-100		SB-300	Widebody
Viper	M-200	TA-100		SB-300	Widebody
Dragonfist	M-200	TA-100		SB-300
Cue	M-200	TA-100		SB-300
Flight 2000	M-200	TA-100		SB-300	Uses voice module VSU-100, widebody
Free Fall	M-200	TA-100		SB-300	Uses voice module VSU-100, widebody
Lightning	M-200	TA-100		SB-300	Uses voice module VSU-100, uses interface board for bonus display in playfield
Split Second	M-200	TA-100		SB-300	Uses voice module VSU-100, widebody
Catacomb	M-200	TA-100		SB-300	Uses voice module VSU-100
Orbitor 1	M-200	TA-100		SB-300	Uses voice module VSU-100, widebody

3 Technical Info

3.1 The Bally / Stern Board Set

The Bally/Stern boardsets always consist of a rectifier board, a solenoid driver/power regulator board, a lamp driver board, and an mpu board. These boards utilize the Motorola 6800 series of microprocessors, 2 peripheral interface adapter chips (6821 PIAs), a switch matrix, multiplexed gas plasma displays, and direct driving of lamps and solenoids (no matrix). Lamps are switched on near the zero crossing 120 times a second to prevent premature lamp filament burnout.

Additional boards present in games may include various flavors of sound boards, as well as additional lamp driver boards (both main and auxiliary), solenoid expander boards, specialized boards such as an echo (say-it-again) board, and speech boards.

The software utilized in these games is very similar to one another, consisting of an "operating system" and a "game rom"; Bally utilized a masked rom for their OS over several games, enabling many roms to be ordered at one time for lower manufacturing cost. Stern custom compiled their operating system for each game, although some games have the same exact rom codes, differing switches in each of those affected games perform different functions although the rulesets are the same/very similar to one another.

Starting with the Stern Mpu-200 series of games (Meteor, 1979), Stern utilized a state machine architecture, where the core operating system handles the various housekeeping functions (displays, switch reading, memory management, lamps/solenoid driving, etc.) and the state layer handles things like game rules and timing of lamp and sound effects. This enabled the programmers to concentrate on defining their rulesets and lamp effects instead of tweaking timing within the assembly code itself. The state machine is multi-threaded and is able to execute up to 16 threads at one time.

Bally games continued to use a real-time setup, where all functions are coded in 6800 assembly language, necessitating lots of additions to the operating system over the years to enable more sophisticated light and sound effects/choreography. Contemporaries of Bally (Gottlieb, Stern, and Williams) all switched to the state machine architecture at some point in their solid state eras. The coding speed advantage of the state machine enabled more rapid development of software, a distinct advantage when production runs started to become shorter and shorter.

3.2 Recommended Documentation

Schematics for each game are essential in tracing down connections to lamps, switches, and solenoids. The owner's manual is a handy resource to have for dip switch settings as well as audit information.

Less important but still handy are the Bally Theory of Operation manual and the Repair Manuals. The repair manuals are written with the use of a test fixture called an Aid1 in mind (essentially a specialized logic probe).

The early -17 Bally games as well as the early stern mpu-100 games have both an owner's manual and a separate schematic package available. If buying documentation on ebay or the like, be sure to check with the seller to see what is included. Most documentation is also available via ipdb.org although the quality of some of the scans make it difficult to extract the needed information. Be aware that although rare, some factory documentation contains errors in schematics as well as game descriptions and settings.

3.3 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

3.4 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

3.5 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 (columns), (starting with 0, ending with 4), and 8 switch returns (rows), (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 1N4004 diode, or in some cases a 1N4148 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 Centaur, 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.

3.6 Bally and Stern MPU Boards

Bally AS-2518-17 MPU Board

Bally AS-2518-35 MPU Board

Bally 6802 MPU Board (A080-91638-D000)

Stern M-100 MPU Board

Stern M-200 MPU Board

All Bally and Stern MPU boards are built around the Motorola 6800 series CPU chip and 6820 or 6821 peripheral interface adapters (PIAs).

32 pins at J5 of a -17 MPU

33 pins at J5 of a -35 MPU

In most cases, if a Bally MPU board has taken a bad hit from alkali damage, the bottom right corner of the board typically takes a hit. Unfortunately, the bottom right corner of the board is also the location where the board number is stenciled onto the masking. If the masking has delaminated, it will take the stenciled board number information with it. At this point, it would be difficult to determine what board it actually is.

However, there is a quick and easy way to determine whether the board is either a -17 or -35. Simply look at the J5 header pin connection located at the top center of the board. If there are only 32 pins (including one empty key) at the connection, the board is a -17. If there are 33 pins (including one empty key) at this connection, the board is a -35.

The Bally 6802 MPU board was only found in two games and in small quantities before the introduction of 6803 games. Some specifics of the 6802 board can be found here.

3.7 Transformers

Manufacturer	Part Number	Power Transformer Module	Rectifier Board Assembly	Winding 1	Winding 2	Winding 3	Winding 4	Winding 5
Bally	E-122-125	AS-2877, AS2877-1	AS-2518-18	49VAC	173VAC	7.3VAC	7.8VAC	12VAC
Bally	E-122-131	AS-2877-3	AS-2518-49	49VAC	173VAC	7.3VAC	9.2VAC	12VAC
Bally	E-122-141 / AS-3071-2	AS-2877-6	AS-2518-54	49VAC	170VAC	6.5VAC	8.2VAC	14.2VAC
Bally	E-122-142 / AS-3071-2	AS-2877-6	AS-2518-54	49VAC	170VAC	6.5VAC	9.4VAC	14.2VAC
Bally	E-122-170 / AS-3071-15 ‡	AS-2877-13 ‡	AS-2518-151 ‡	49VAC	170VAC	8.5VAC	20V CT †	14.2VAC
Bally	AS-3071-12 §	AS-2877-11 §	AS-2518-132 §

† Center Tapped
‡ Goldball and Grand Slam only.
§ Baby Pacman and Granny & The Gators only

3.8 Rectifier Boards

The rectifier board is the first part of the power train in any Bally or Stern machine. In addition to rectifying four discrete AC voltages to DC, the rectifier board consists of the bulk of fuses for the game, including the main fuse. After all associated voltages are fused, the power is dispersed to the backbox, playfield, and lower cabinet.

++++ Add more later, explain differences between -18 and -49 (Space Invaders / Kiss) rec. boards ++++

There are two revisions of the AS-2518-54 rectifier board. The first revision has 5 fuses. Revision "B" has an additional fuse. On revision B, two fuses are used for the general illumination instead of just one fuse. One fuse is for the GI on the playfield, and the second fuse for the GI in the backbox. The AS-2518-132 rectifier board (used only in Baby Pac-Man and Granny & The Gators) is based on the AS-2518-54 revision B board.

The AS-2518-132 rectifier board is only used in Bally's two hybrid games--Baby Pac-Man and Granny & The Gators. The AS-2518-132 board backwards compatible with the AS-2518-54 board. However, in order to use a standard AS-2518-54 board in a hybrid game, the rectifier diodes at CR5, CR6, CR7, and CR8 need to be upgraded from the stock 3 Amp diodes to 6 Amp diodes.

Bally AS-2518-18 Rectifier Board
Bally AS-2518-49 rectifier board
Bally AS-2518-54 Rectifier Board
Bally AS-2518-54 Revision B Rectifier Board. Two fuses are used for the general illumination instead of one (the GI for the playfield and the GI for the backbox)
Bally AS-2518-132 Rectifier Board. Only used in Baby Pacman and Granny & The Gators.
Bally AS-2518-151 Rectifier Board

Early Stern TA-100 Rectifier Board
Later Stern TA-100 Rectifier Board
Later Stern TA-100 Rectifier Board (blank)

3.8.1 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.

Bally AS-2518-18 Rectifier Board (Solder Side)

Board Connection	Wire Color / Gauge	Transformer Lug	Circuit
E1	Red 18 AWG	5	Primary AC Hot
E2	Yellow 18 AWG	1	Primary Neutral
E3	Red 20 AWG	2	Solenoid Bus Hot
E4	White/Red 20 AWG	6	Solenoid Bus Neutral
E5	Green 20 AWG	8	Display High Voltage Hot
E6	White/Green 20 AWG	10	Display High Voltage Neutral
E7	Blue 18 AWG (2 wires)	17	GI Bus Hot
E8	Black 18 AWG (2 wires)	18	GI Bus Neutral
E9	Orange 18 AWG	13	Controlled Lamp Bus Hot
E10	Green 18 AWG	14	Controlled Lamp Bus Neutral
E11	White 20 AWG	15	12V Input for 5-Volt Regulator Hot
E12	White/Black 20 AWG	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

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

Stern TA-100 Rectifier Wire Color connections

As 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.

3.8.3 How To Properly Mount a Bally AS-2518-54 Rectifier Board

Bally AS-2518-54 Rectifier Board

Bally AS-2518-54 Rectifier Board (back)

The Bally AS-2518-54 rectifier board normally mounts on a large metal plate found in the bottom of the pinball machine’s cabinet. It uses the metal plate as a heat sink for the two large bridge rectifiers on the underside of the board, so mounting it properly is important. Carefully following the steps illustrated below will ensure the board is correctly mounted for long term reliability.

Mounting a Bally -54 rectifier board
Locate the two mounting holes for the bridge rectifiers, circled in red, and the seven mounting holes for the circuit board, circled in yellow.
Practice laying the board in the proper position once, so you’re sure you know where it goes. You want the two holes that go through the bridge rectifiers to line up with the holes in the plate. Also make sure the mounting screws around the edge of the board are lining up with their holes too.
Prep the surface of the mounting plate by cleaning the area, where the two bridges will mount, with some alcohol or acetone.
Make a circle of heat sink grease around each bridge mounting screw hole approximately the diameter of a dime. Heatsink grease is available from most all the popular vendors.
Carefully place the rectifier board in back on the mounting board. You want to get the board positioned as best as you can without moving it around a lot or you will smear the heat sink grease all over the place. What I like to do is peek through one of the two mount holes on the board and locate the corresponding screw hole on the plate. Then as you peek through this hole, guide the board into place while keeping the screw hole in sight.
Double check your work, being careful not to move the board around too much. To avoid smearing the heat sink grease, it’s best if you can place it directly into the proper position the first time, without having to scoot it around afterwards.
Next, start the two mounting screws that go through the bridge rectifiers, but do not tighten them all the way.
Now locate and install the remaining seven mounting screws along the perimeter of the board, but don’t tighten them all the way yet. Since all the screws are a little loose, you have a little bit of board movement available to help locate the mounting screw holes on the plate.
Once all the perimeter screws are in place, tighten the two bridge rectifier screws. You want them nice and tight so it spreads the heat sink grease into a nice, evenly spread thin layer. Just be careful that you don’t strip the threads out of the mounting holes. Then tighten up the perimeter screws after that.
All done!
One word of warning: The mounting screws protrude way past the bottom of the board, so be careful where you place this assembly. The screws may scratch your workspace (a nice table, countertop, etc.).

3.9 Bally and Stern Solenoid Driver Board

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 of all, everything mentioned in the following sections specifically reference the Bally AS-2518-22 solenoid driver board, found in most Bally pins from 1977 through 1985. Since the Bally AS-2518-16 and Stern SDU-100 boards are very similar, and all are identical as far as the operation of the solenoid driver circuits, the information is applicable to these boards as well. The main differences between Bally and Stern solenoid driver boards used from the factory are the physical layout of parts, and whether or not the board is single-sided or double-sided. Since the physically connector locations are the same, Bally and Stern solenoid driver boards are similar enough to be interchangeable.

Secondly, if all this is Greek and you have no idea how decoder ICs work, or what a transistor is, take a look at the How Bally Coils are Driven for Dummies section to learn the basics of how things work.

Third, the solenoid driver board actually has three functions.

Drive the solenoid and relay coils of a pinball machine.
Regulate the logic voltage which provides a nice and steady +5VDC to the other boards for their various logic circuits.
Regulate the high voltage (+190 VDC) for the display driver boards

The regulated voltage will not be discussed here, only the solenoid drive section.

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 butt. A shock from 190 volts DC will hurt. If you don't know what you're doing, stay away from it and have a professional fix it instead. In addition to high voltages, there are static sensitive parts on these boards. While working on boards, be sure to properly ground yourself before touching the board, and always work in a static-free workspace.

3.9.1 Stern Driver Board Revisions

There are several versions of the Stern SDU-100 driver board. Revision A is the most radically different than all the other versions, since it has a blue solder mask and hand-drawn traces. This revision can have either "Rev 1" or "Rev 2" printed on the board below the "SDU-100" label.

Revision B is marked as "B432" in the lower right hand corner. There is a lot of extra masking and labels on this board that are not seen on any other revisions.

Revision C is is marked as "Revision C" in the center of the board. A fuse was added for the high voltage section for the displays. However, this fuse was proven to be largely useless, and did not blow if there was a short in the high voltage section's regulation transistors.

The final revisions of the board lacked a fuse, but included a shutdown transistor in the high voltage section intended to cut the high voltage power if there is a short in this section (however, this is not always successful depending on where the short is). The later revisions went up to revision D, and possibly E or F, but this is currently unconfirmed.

SDU-100 Revision A (Rev 1 and Rev 2)
SDU-100 Revision B (B432)
SDU-100 Revision C
SDU-100 Revision D/E/F?

3.9.2 How Bally Coils are Driven for Dummies

Typical Bally Coil (Mata Hari)

There are three main characteristics regarding the coils and coil connections in Bally games.

Two big fat yellow wires going to one lug.
The small skinny wire going to the other lug.
The diode connected to the two lugs.

The majority of information in this section is applicable to Stern games too. Bally and Stern solenoid driver boards are similar enough in overall design for them to interchange between games / manufacturers. The only other primary difference between Bally and Stern is the wire color of the solenoid bus line in most cases.

One lug on every coil is connected via a parallel circuit by the fatter wires. This type of connection is also commonly referred to as a daisy-chained circuit. These fat wires supply 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 only have one. Flipper coils have these wires too, but they are connected a little differently, and are discussed elsewhere. For now, just assume regular solenoids are being discussed here.

Each coil has a small skinny wire on the other lug. This wire goes to the control circuits on the solenoid driver board. In order to energize the coil, there must be a path to ground for the +43VDC. In its at rest state, the coil does not have a path to ground. 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, which 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, there is a diode on each coil. When the current is quickly turned off on an energized coil, the magnetic field around the coil collapses quickly. This action causes the coil to generate a huge voltage spike. The job of the diode is to prevent the majority of this spike from reaching the solenoid driver circuity. If the diode is bad (shorted) or installed backwards, the drive transistor will be destroyed the very first time the coil is energized, then released. The process is similar to the ignition system used 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.

Comparison of Electrical Sine Waves

The computer program that runs the machine also tries to limit this spike by turning off the coil near the zero crossing of the AC line. This helps because the DC that drives the coils is rectified, but not filtered, so it's not smooth DC, but "humpy", as shown in the adjacent picture.

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

Depiction of Multiple Coils in a Bally Game with Manual Switches Inserted and tied to Ground

So, in the simplest form, the solenoid driver circuits in a Bally game look like what is shown in the accompanying pic. Look at it as a bunch of coils all connected to the +43VDC bus, and the other lugs going to switches which are connected to ground. If a switch were to close, it would connect the circuit from +43VDC to ground, and the coil would energize as long as the switch is closed.

One Switch Closed and Energizing the Coil

See how the circuit is complete due to the switch being closed, and the coil is energized. When the switch is opened again, the coil turns off, and is returned to the same state as the previous picture. If the diode were not there, there would be a big arc across the switch contacts upon the moment they opened up.

Depiction of Multiple Coils in a Bally Game with Transistors Shown

Now, 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 the Bally solenoid driver, the emitter and collector can be used like a switch. With no current supplied to the base, there is no current flow between the collector and emitter - the transistor switch is open, or OFF. If current is supplied to the base, the 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 has the effect of connecting the collector to ground. This completes the circuit to the coil and it turns on (fires).

A coil can be tested by momentarily grounding the tab on the coil's drive transistor. For the TIP-102 or similar transistors used in the Bally solenoid driver, the metal tab is connected to the collector. Knowing this, and what was just discussed, grounding the tab is the same as grounding the collector, which will complete the circuit to ground and fire the coil. However, this test only tests the wiring from the solenoid driver to the coil. It DOES NOT test the transistor itself or any circuitry before the transistor.

The transistor and "control signal" in the simplified drawing above can be replaced with the actual circuit. More details regarding this circuit are found in the following section.

3.9.3 Overview

Two circuit boards will be discussed: 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.

3.9.4 How the Solenoid Driver Works

The solenoid driver is responsible for energizing the solenoid coils of the 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 (+5vdc). When strobed, the decoder lowers one of it's sixteen output lines, depending on the pattern of the four input signals. Detailed info about the 74LS154 decoder chip is availalbe here.

Typical Solenoid Driver Circuit

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 seven in the CA3081 transistor array 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 40vdc 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 +5vdc 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 40vdc 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.

3.10 Lamp Driver Board

Bally and Stern controlled lamps are driven discretely via SCRs located on the lamp driver board. Because of this, neither manufacturer utilizes a lamp matrix. Any variation of the lamp driver boards are capable of controlling a maximum of 60 discrete lamp circuits. Typically the 2N5060 SCRs can only control one lamp, while the MCR106 / SCR106 / C106 SCRs can control up to two lamps.

The first generation of both the Stern and Bally lamp driver boards has 4050 hex buffer chips installed between the 4514s and the MCR106 SCRs. It is unknown why both companies chose to remove these chips from later designs.

Bally Lamp Driver Boards
AS-2518-14, Rev. 2
AS-2518-23
AS-2518-23, Rev. 1
AS-2518-23, A000

Stern Lamp Driver Boards
LDA-100
LDA-100 Rev. B
LDA-100 Rev. C

3.11 Combination Solenoid / Lamp Driver Board

File:Bally AS-2518-107 Partially stripped.JPG

Bally AS-2518-107 Combination Solenoid / Lamp Driver Board (Note that the board shown is missing the 5v regulator and heat sink, the 5v filtering capacitor, and several other discrete pieces)

Bally AS-2518-147 Combination Solenoid/Lamp Driver Board. This board integrates 5V and display voltage regulation, along with lamp and coil drivers, onto a single board. Image courtesy of Collin Foust.

3.12 Vidiot Board

Bally AS-2518-121 Vidiot Board (Note that some chips have been pulled from their sockets on this board)

Bally created two Hybrid video/pinball games, Granny and the Gators and Baby Pac-Man, which included a video game monitor and a pinball playfield. The Vidiot board is a special circuit board used to operate the video game portion and sounds of the hybrid games. However, each game used a slightly different Vidiot board. Baby Pacman used a "Vidiot Board", while Granny and the Gators used a "Vidot Deluxe Board". The two boards are not interchangeable.

3.13 Miscellaneous Boards

3.13.1 Solenoid Expander Board (AS-2518-66)

Bally Solenoid Expander board- Arrow indicates necessary bulb

The Solenoid Expander board was used in several Bally games. Its purpose is to enable a particular coil or to multiplex several coils. It is typically driven by a lamp SCR on the lamp driver board versus a solenoid transistor on the solenoid driver board. However, at least Centaur and Centaur II are exceptions. Both games drive the solenoid expander board via the Q11 transistor on the solenoid driver 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 (MOC3011) on the expander board needs a load to work. Neither Centaur nor Centaur II use this bulb.

3.13.2 Auxiliary Driver - GI Flasher (AS-2518-68)

Placeholder for Bally Auxiliary Driver Board

The auxiliary driver board is used on some Bally games to drive a triac, which in turn switches some of the general illumination on and off for effect. It is typically driven by a lamp SCR on the lamp driver board. The driven triac is typically located on a bracket which is attached to the rectifier board mounting plate in the bottom of the cabinet.

Much like the solenoid expander board, there is a 555 bulb near the auxiliary driver board that lights when the auxiliary driver board is activated. This bulb is essential for proper operation of the auxiliary driver, as the opto isolator chip (MOC3011) on the board needs a load to work.

3.13.3 Strobe Board

The Bally strobe board was used on Flash Gordon. A small transformer in the cabinet bottom provides the voltage required for this board. That power is fused by an "in-line" fuse at the small transformer.

There isn't much to go wrong with this board as it's comprised of a few diodes and resistors. Other than replacing the actual strobe lamp and the "trigger" transformer, parts are easy to find. Some folks have been successful using a strobe lamp acquired from Radio Shack. A source for the trigger transformer is unknown.

The trigger transformer should measure about 32 ohms between the pins marked 1 and 2, and about .2 ohms between the pins marked 3 and 4.

If your strobe is producing a very weak strobe, or not working at all, test the two 22uf/250V electrolytic capacitors. Simply replacing out of spec capacitors may bring the strobe back to life.

Another area for concern, as with all single sided PCBs is the header pins. Replacing these pins or simply reflowing the solder on them is a good idea as they are subject to cracked solder joints.

If working properly, the strobe will fire 4 times at game power up. It also strobes along with the controlled lamps during "all lamp" test. It obviously will strobe during game play too.

Flash Gordon Strobe Board Components
Bally Strobe Lamp Board as found on Flash Gordon (front), with new 22uf capacitors.
Bally Strobe Lamp Board as found on Flash Gordon (rear).
The "HAL-9000 like eye" strobe lamp as seen from the front of the lamp insert panel.
Small transformer and in-line fuse in cabinet bottom.

3.14 Displays

Here are some different types of Bally displays

Bally 6 and 7 digit displays
AS-2518-21 6-Digit Display
AS-2518-15 6-Digit Display
AS-2518-58 7-Digit Display

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

Stern 4, 6, and 7 digit displays
4-Digit Display
DA-100 6-Digit Display (Double-Sided)
DA-100 (Rev B) 6-Digit Display (Single-Sided)
DA-100 6-Digit Display (Single-Sided)
Different DA-100 6-Digit Display (Single-Sided)
DA-300 (Rev A) 7-Digit Display
DA-300 (Rev B) 7-Digit Display
DA-300 (Rev C) 7-Digit Display

3.14.1 Bally 6-Digit Displays

A healthy Bally 6-Digit Display

The following 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 displays 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.

Example of a Bally AS-2518-15 6-digit display

Example of a Bally AS-2518-21 6-digit display

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 the Power Play Owner's Manual) is the "-21". The two shown here were upgraded with 1/2 watt 100K ohm resistors. A modification that should be done on all displays.

Example of a Stern 6-digit display

Likewise, there are different versions of Stern 6-digit displays. These displays are interchangeable with all Bally and Stern games.

3.14.1.1 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 it is not visible. 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.

Each display has six digits, and upon closer inspection, 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!

There are 4 main "parts" of a display assembly:

The glass display itself
The display driver consisting of the input decoder
The six digit driver circuits
The 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. 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 onto its 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.

Labeled Segments and Truth Table

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. 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. 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. Please see the 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.

Before explaining how the computer makes all this work, let's summarize: 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.

3.14.1.2 How The Computer Controls The Display

The next thing to understand is how the computer in the pinball machine operates the displays. For this section, referenced MPU board will be the AS-2518-17 module, but all this also holds true for the "-35" MPU module as well. And again, the Bally AS-2518-21 and AS-2518-15 Display Drivers will be referenced. 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.

Display Signals from MPU Board Illustrated

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.

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.

3.15 Bally Auxiliary Lamp Driver Boards

Bally AS-2518-43 Aux. Lamp Driver Board

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

To increase the total of controlled lamps used in a particular game, Bally implemented auxiliary lamp driver boards. These aux. lamp driver boards were either used for effect (chaser or infinity lamps used between backglasses in games such as Xenon or Space Invaders), additional controlled insert lamps, or both (top rollover insert lamps and Queen's Chamber chaser lamps used on Centaur).

There are essentially only two different boards used in games. The first is an AS-4518-43. This is the smaller footprint board, which has only one output connection. It is capable of driving 12 discrete circuits or a total of 24 lamps (12 sets of 2 lamps).

Outputs for AS-4518-43 Aux. Lamp Driver Board
J2 Header	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
Output	Q1	Q2	Q3	KEY	Q4	Q5	Q6	GND	GND	--	Q7	Q8	--	--	--	--	Q9	Q12	Q11	Q10

Bally AS-2518-52 Aux. Lamp Driver Board

The second board is the AS-4518-52. This board is narrower, yet longer in construction. It is capable of driving 28 discrete circuits or a total of 56 lamps (28 sets of 2 lamps). Either aux. lamp driver board receives the same inputs from the CPU board. Likewise, these signals are identical to the signals sent to the primary lamp driver board. The only differing signal between the primary lamp driver board and either aux. lamp driver board is the lamp strobe. The primary lamp driver board receives lamp strobe 1, while the aux. lamp driver boards receive lamp strobe 2.

Outputs for AS-4518-52 Aux. Lamp Driver Board
J2 Header	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	--	--
Output	--	--	KEY	Q2	Q7	Q6	Q1	Q3	Q5	Q4	Q9	Q14	Q13	Q8	Q10	--	Q12	Q11	--	--
J3 Header	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
Output	--	KEY	Q16	Q21	GND	GND	Q20	Q15	Q17	Q19	Q18	Q23	Q28	Q27	Q22	Q24	Q26	Q25	GND	GND

3.16 Bally Sound Boards

3.16.1 Bally AS-2518-32 Sound Board

Bally AS-2518-32 Sound Board with 2 pots

Bally AS-2518-32 Sound Board with 3rd pot at R35

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
Grand Slam	TBD	B, D
Future Spa	E781-2, E781-5 (or sub with E781-13)	B, C
Nitro Groundshaker	E776-14, E776-15	B, C
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)

Bally AS-2518-56 Sounds Plus Board

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 Vocalizer Speech Board (AS-2518-57)

Bally AS-2518-57 Vocalizer Board

Bally AS-2518-57 Vocalizer and Sounds Plus Boards Insitu

The Vocalizer board was only used in Xenon and very early Flash Gordons. It is a complimentary board to the AS-2518-56 Sounds Plus board, and contains the numerous roms needed for an extensive speech vocabulary.

3.16.6 Squawk & Talk Sound Board (AS-2518-61)

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 4 variations of the board: -61, -61a, -61b and -61d.

Some variations of this board have a J3 header connection located at the top upper left edge of the board. This connection was never implemented. Likewise, some boards are populated with a 2 x 20 pin .100" header connection located on the left edge of the board. This connection is marked on the schematics for the use of a vocalizer, which was never implemented.

All of the different variations of this board should work on all games. The exceptions are Centaur and Centaur II. These two games must use the -61b board. The reason for this are the extra input / output connections at J2 (bottom right of board) needed for connection to the Say It Again board. A standard -61 or -61a has a total of 6 header pins at J2, while the -61b has a total of 10 header pins.

4 Revisions of the AS-2518-61 Squawk and Talk Sound Board
AS-2518-61 Squawk & Talk Sound Board
AS-2518-61a Squawk & Talk Sound Board
AS-2518-61b Squawk & Talk Sound Board. Note expanded connector at J2 (lower right).
AS-2518-61d Squawk & Talk Sound Board installed in VECTOR.

3.16.6.1 Squawk & Talk Jumper Settings

Bally Squawk & Talk Jumper Locations. Note that the -61B revision of the board contains a jumper FF located within the stack of resistors below the AD558. Neither the -61 or the -61a revision has this jumper.

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 with a 6810 chip, install L, remove K
If using a 6802 CPU chip, install K, remove L. The 6810 can be removed if using a 6802, but doesn't impede proper operation if left in place
The 5 EE jumpers must be installed when the AY-8912 chip is not present.
The -61B revision of the board has an FF jumper, located in the stack of resistors below the AD558. This jumper should be IN if the "Say it again" board (reverb) is not used or connected. With the "Say it again" board in use, jumper FF should be OUT.

Game	Original Jumper settings as shipped with factory configured ROMs
Flash Gordon	C, D, E, G, Q, S, U, W, Y, AA, H, DD, N, and L or K
Eight Ball Deluxe	C, D, E, G, Q, S, U, X, Y, AA, H, DD, N, and L or K
Fireball II	C, D, E, G, Q, S, U, X, Y, AA, H, DD, N, and L or K
Embryon	C, D, E, G, Q, S, U, X, Y, AA, H, DD, N, EE, and L or K
Fathom	C, D, E, G, Q, S, U, W, Y, AA, H, DD, N, EE*, and L or K
Medusa	C, E, G, Q, S, U, W, Y, BB, D, H, DD, N, EE, and L or K
Elektra	C, E, G, Q, S, U, W, Y, BB, D, H, DD, N, and L or K
Centaur	C, E, G, Q, S, U, W, Y, BB, D, H, DD, N, EE, FF (if no SIA board), and 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, and L or K
Spectrum	C, D, E, G, Q, S, U, W, Y, BB, H, DD, N, EE, and L or K
Vector	C, D, E, G, Q, S, U, W, Y, AA, H, DD, N, and L or K

Source: Bally / Midway 1982 parts catalog.

*Note: Even though the parts catalog states otherwise, Fathom more than likely uses the EE jumpers. Please confirm.

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

3.16.7 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.

3.16.8 Cheap Squeak Sound Board

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

The Cheap Squeak was designed as a lesser expensive sound board. It only utilizes a 6803 microprocessor, which allows it to function without 6821 PIAs and external ram memory. This sound board is only capable of simple tones and sounds and no speech.

The following -35 games use the Cheap Squeak:

Black Pyramid
Cybernaut
Fireball Classic
Kings Of Steel
Spy Hunter
X's & O's

Lady Luck, a 6803 based game, also uses this sound board.

At power up, the Cheap Squeak's LED will flicker briefly, then flash, flash again, then turn on and 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. The LED May turn on and off when sounds are playing or idle, but this is not always the case. With some games (Kings of Steel, X's and O's, and Black Pyramid), after the sound board successfully boots, the LED remains on.

There are differing results when pressing the self test button depending on the sound ROMs. For example, pressing the self test with Black Pyramid ROMs results in a differing tone played every time. While pressing self test with Kings of Steel or X's and O's ROMs, causes the sound board to play the same sound each time.

Board Theory of Operations
The 6803 (U1) microprocessor multiplexes A0-A7 with D0-D7, calling those signals AD0-AD7. The processor fetches information from the sound ROMs (both code to execute and sound clips) by placing address information on AD0-AD7 and strobing the processor's AS (address strobe) signal to the 74LS373 (U2), thereby latching the lower 8 bits of the address bus in the LS373. A8-A15 are used along with jumpers JW1 through JW12, to implement a memory mapped I/O scheme to address the 2 sound ROMs which can be 2532s, 2732s, or 2764s. A14 and A15 control the 74LS10 (a triple 3-input nand gate) to assert device selects to the ROMs.

Note that the processor does not use the traditional R/W signal as it never "writes" to memory. Besides placing instruction address and data on the address and data busses, the processor reads sound selects via P20-P24 and writes sound data to the DAC via P10-P17. Think of these lines as PA1-PA7 of a 6821 or 6532.

The 6803 is initialized by the MPU at power up into 6803 mode N. Once initialized and running, the sound ROM code running in the 6803 accepts sound signal commands and merely reads pre-formatted sound "clips" from the sound ROMs and then writes the data to the ZN429 (U6) digital-to-analog converter (DAC) 8 bits at a time. The DAC converts the digital data to an analog level which is presented to the amplifiers for output to the speaker(s).

The board creates 5VDC on board by regulating 12VDC down to 5VDC. Unregulated 12VDC enters the board at J1-10. It is filtered by C8, C9, and C10. The inductor at L1 smooths the voltage somewhat. D6 (VR332, equivalent to a 1N5402), D7, and D8 drop the voltage by .5 - .7 volts (normal voltage drop across a diode). The 7805 at U9 further regulates the voltage down to 5VDC which can be measured at TP2 (TP3 is ground).

This 5VDC is used to power the TTL logic ICs. The ZN429 DAC also uses this 5VDC as a voltage reference. To prevent the sound volume from fluctuating over the range of operating temperatures, the reference voltage is held constant by a "voltage divider biasing circuit" comprised of resistors at R22, R23, and R24, and a 2N5305 NPN transistor at Q7. This reference voltage is presented at pin 5 of the DAC.

Test Points

TP1 should measure about 11VDC.
TP2 is 5VDC.
TP3 is ground.
TP4 is the clock signal, provided externally by the 6803 for the purpose of synchronizing address and data read cycles.
TP5 is the reset signal, which is also present on pin 6 of the 6803.

3.16.8.1 Cheap Squeak ROMs & Jumper Settings

Bally Cheap Squeak Sound Board with Jumpers Highlighted

General EPROM Configuration	Jumpers Connected
U3 & U4 using 2532s	J6, J9, J12
U3 & U4 using 2732s	J7, J10, J11
U3 ONLY using 2764 (works only for Cybernaut and X's & O's)	J2, J4, J7, J11

Sound ROM Configuration and Behavior by Game

Game	EPROM Configuration Tested	Jumpers Connected	LED Boot Behavior	SW1 Tune	Boot Tune
Cybernaut	U3 - 2764, U4 - nu	J2, J4, J7, J11	Flicker, Blink, Blink, On	Space Ship Landing	Ding followed by Decaying Buzz
X's & O's	U3 - 2764, U4 - nu	J2, J4, J7, J11	Flicker, Blink, Blink, On	Single Chime that decays	Single Chime that decays
Spy Hunter	U3 - 2732, U4 - 2732	J7, J10, J11	Flicker, Blink, Blink, On	Cartoon Electrical Short Circuit	Chime followed by Rising Laser
Lady Luck			Flicker, Blink, Blink, On	Explosion
Black Pyramid	U3 - 2732, U4 - 2732	J7, J10, J11	Flicker, Blink, Blink, On	Random Pitched Chime	Ding followed by Decaying Buzz
Kings of Steel	U3 - 2732, U4 - 2732	J7, J10, J11	Flicker, Blink, Blink, On	Bell	Chime followed by Rising Laser

After pressing the test switch (SW1), a sound is played, and then the board reboots itself.
Note: Combining 2732 images into a single 2764 does not work for Black Pyramid, Fireball Classic, Kings Of Steel, or Spy Hunter.

3.16.9 Bally Sound Board Pinouts

NC = not connected, and verified.
Not all N/U have been verified as NC. Some may actually be NC.

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
J1-1	Sol. Address A	Sol. Address A	Sol. Address A	Sol. Address A	Sound Select	Sound Select	Sound Select	Sound Select
J1-2	Sol. Address B	Sol. Address B	Sol. Address B	Sol. Address B	Sound Select	Sound Select	Sound Select	Sound Select
J1-3	Sol. Address C	Sol. Address C	Sol. Address C	Sol. Address C	Sound Select	Sound Select	Sound Select	Sound Select
J1-4	Sol. Address D	Sol. Address D	Sol. Address D	Sol. Address D	Sound Select	Sound Select	Sound Select	Sound Select
J1-5	+5VDC	+5VDC	+5VDC	+5VDC	N/U	NC	N/U	N/U
J1-6	Ground	Ground	Ground	Ground	Ground	Ground	Ground	Logic Ground
J1-7	NC	N/U	N/U	N/U	Gen. Ill. Bus (6VAC)	Gen. Ill. Bus (6VAC)	Gen. Ill. Bus (6VAC)	N/U
J1-8	Sol. Bank Select	Sol. Bank Select	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt	Sound Interrupt
J1-9	+43V	+43V	N/U	N/U	N/U	NC	N/U	N/U
J1-10	NC	N/U	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated	+12V Unregulated
J1-11	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
J1-13	N/U	N/U	N/U (Spare Address Line)	N/U (Spare Address Line)	N/U	NC	N/U	Earth Ground
J1-14	Ground	Ground	Ground	N/U (Ground)	Ground	Ground	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
J1-16	n/a	n/a	n/a	n/a	n/a	+12V Unregulated Return	+12V Unregulated Return	n/a
J1-17	n/a	n/a	n/a	n/a	n/a	+12V Unregulated	+12V Unregulated	n/a
J1-18	n/a	n/a	n/a	n/a	n/a	N/U	N/U	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
J2-1	Speaker +	Speaker +	Speaker -	Speaker -	Speaker -	Speaker -	Speaker -	Speaker -
J2-2	Speaker -	Speaker -	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +	Speaker +
J2-3	n/a	n/a	n/a	n/a	Key	Key	Key	n/a
J2-4	n/a	n/a	n/a	n/a	Remote Volume Return	Remote Volume Return	Remote Volume Return	n/a
J2-5	n/a	n/a	n/a	n/a	Speech Volume	Speech Volume	Speech Volume	n/a
J2-6	n/a	n/a	n/a	n/a	Sound Volume	Sound Volume	Sound Volume	n/a
J2-7	n/a	n/a	n/a	n/a	n/a	n/a	Reverb Audio In	n/a
J2-8	n/a	n/a	n/a	n/a	n/a	n/a	Shield Ground	n/a
J2-9	n/a	n/a	n/a	n/a	n/a	n/a	Audio Out	n/a
J2-10	n/a	n/a	n/a	n/a	n/a	n/a	Shield Ground	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
J3-1	n/a	n/a	n/a	n/a	n/a	n/a	Ground	n/a
J3-2	n/a	n/a	n/a	n/a	n/a	n/a	Data	n/a
J3-3	n/a	n/a	n/a	n/a	n/a	n/a	Clock	n/a
J3-4	n/a	n/a	n/a	n/a	n/a	n/a	+5VDC	n/a
J3-5	n/a	n/a	n/a	n/a	n/a	n/a	Key	n/a
J3-6	n/a	n/a	n/a	n/a	n/a	n/a	PB3	n/a
J3-7	n/a	n/a	n/a	n/a	n/a	n/a	PB2	n/a

3.17 Stern Sound Boards

3.17.1 Stern SB-100 Sound Board

Stern SB-100 Sound Board - 1st Generation

The first generation SB-100 sound board was used on the earliest Stern games with electronic sound. These boards were fully populated, because in addition to electronic sounds, there was a (simulated) chimes option (typically dipswitch setting 23 on M-100 MPU boards). Although they will have higher pitched sounds, the first generation boards are compatible with all Stern games using the M-100 MPU board and electronic sounds. With some modifications, this board can be made to sound like the lower pitched 3rd generation board.

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

The second generation SB-100 sound board was used on Stern games with electronic sound and no chime sound option (typically dipswitch setting 23 on M-100 MPU boards). Due to the lack of the optional chime sounds option, this board is less populated. Although they will have higher pitched sounds, the second generation boards are compatible with all Stern games using the M-100 MPU board and electronic sounds, which did not use the chime option. With some modifications, this board can be made to sound like the lower pitched third generation board.

Stern SB-100 Sound Board - 3rd Generation (C-1 - less populated)

The third generation SB-100 sound board was used on some of the last Stern M-100 games with electronic sound and no chime sound option. Like the second generation board, due to the lack of the optional chime sounds, this board is less populated. The difference with this board and the second generation board is that the component markings and through holes have been removed where components are no longer used. Although they will have lower pitched sounds, the third generation boards are compatible with all Stern games using the M-100 MPU board, which did not use the chime option. This board also shipped in the "standard" green PCB variety. This board is easily identified by the large "C-1" notation. Some test points are located in different positions compared to the first two generations, and TP9 is omitted.

3.17.2 Stern SB-300 Sound Board

Stern SB-300 Sound Board

The Stern SB-300 sound board was used in all games which used the M-200 MPU board. The SB-300 is interfaced to the MPU board via the 34 pin J5 connector located at the top of the board.

Note that the sound board only uses pins 1-32 on its J1 connection. Some ribbon cables used were 2 - 16 pin connections, while others were 2 - 17 pin connections, or a combination of the two.

Make certain that pin 34 of the sound board is not connected to the MPU. Pin 34 on J1 of the sound board and pin 34 on J5 of the MPU board is the /IRQ signal. This signal is never used by the sound board. However, if it is connected to the MPU board from the sound board, it can sometimes cause the MPU to lock up or hang. Either bend pin 34 of J1 on the sound board away from the connector (if it is even connected), or snip the pin off completely.

3.17.2.1 Stern VSU-100 Speech Board

Stern VSU-100 Speech Board

The Stern sound board and speech boards shown installed in a game

The Stern VSU-100 speech board was used as a complimentary board to the SB-300 sound board. In other words, Stern never designed a sound board which was capable of both sound and speech. The speech synthesis is based on the S14001A speech chip. They are pricey, but still available.

3.18 Speakers

All Bally -35 and -133 games use a speaker, Bally -17 games do not. In some cases, games use more than one speaker. The early games use a very small, low wattage xxx ohm speaker in the bottom of the cabinet.

Typical M-100 speaker from a Hot Hand. Note that the volume control is missing from this unit.

Typical M-200 speaker from a Seawitch

With the exception of the first four Stern M-100 games, which shipped with a 4-bar chime box, all others use a speaker. And most of them have the speaker mounted on a board, aimed at the coin door. The speaker is a 6-1/2", low wattage speaker, but has an odd impedance of 6.4 ohms.

The Stern M-200 games use a single speaker in the lower cabinet. It is a 6-1/2", 8 ohm, low wattage (some are marked 8W) speaker.

3.19 Stern MA-100 ROM Board

Stern MA-100 ROM Board

For the first Stern solid state game, Pinball, a ROM board was initially used. This board was mounted to the backbox and a harness connected the board to the MPU board at the top connector J5.

3.20 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.

3.20.1 Bally AS-2518-35 or AS-2518-133 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.

3.20.2 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

3.20.2.1 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.

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.
On the solder side of the -17 board, run a jumper from U2 pin 18, to U17 pin 11.
On the solder side of the -17 board, cut the trace going to U2 pin 21.
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. Note: Trace cuts were completed using a "ball" cutter in a Dremel. The "cut" is marked with a black marker.

Reference the left picture.

On the solder side of the -17 board, cut the trace leading to U18 pin 4.
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.

Reference the center picture.

On the solder side of the board, cut the trace leading to U2 pin 21.
On the solder side of the board, jumper from U2 pin 21 to U2 pin 24.

Reference the right picture.

On the solder side of the board, cut the trace leading to U6 pin 21.
On the solder side of the board, jumper from U6 pin 21 to U6 pin 24.

Note B Cuts and Jumpers
Solder Side Trace Reroute at U18 and "through hole" to U2, pin 18
U2 Cut and Jumper from pin 21 to pin 24
U6 Cut and Jumper from pin 21 to 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 Bally games. This modification should also work for early Stern games with two original 9316 ROMs at U2 and U6.

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.

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.

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.
Scrape the solder mask from the trace leading to pin 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.

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.
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.
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.
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.

On the solder side of the -17 or MPU-100 board, cut the trace that runs to U2 pin 21.
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.
On the solder side, jump a wire from U2 pin 18 to U2 pin 12.
On the solder side, jump a wire from U2 pin 21 to U9 (6800CPU) pin 24.
On the solder side of the board, cut the trace that runs to U6 pin 21.
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.
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).
On the solder side, cut the trace that runs to U17 pin 2.
On the solder side, cut the trace that runs to U18 pin 4.
On the solder side, add a jumper from U17 pin 2 to U18 pin 4.

Note D Cuts and Jumpers
Component side cut locations
Solder side cuts and added jumpers

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:

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

3.20.3 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	2716	9316	9316	2-3, 5-7, 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 should remove the 5101 RAM at U13, as it will not be accessed directly. (Some of the software depends on the values being read with the lower nibble high (1111 or $F) - they will load the byte expecting $1f for instance and if you leave U13 in, it will return either random values or more likely $10). 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.

3.20.4 Bally -35 2764 EPROM Conversion

These instructions will convert a Bally -35 MPU to use a single 2764 EPROM. Colors in the table will match the wire colors in the example photos.

Bally -35 MPU - 2764 EPROM Conversion Instructions
1.		Remove any PROMs or EPROMs from U1, U2, U3, U4, U5 and U6.
2.		Bend out pins 1, 2, 27, and 28 on a 28 pin EPROM socket so we can solder wires to the pins and install it in socket U2 on the MPU. Pin 26 of the EPROM is not connected. I usually remove this pin from the socket but you can just bend it out and not connect anything to it.
3.		Ensure that there are no jumpers connected to E4, E13, E13a, E11, E9, E12, and E35.
4.		Connect jumpers E7 and E8. This connects EPROM A9 to CPU A9.
5.		Connect EPROM socket pins 1, 27 and 28 to +5V. I chose to use pin 24 of U3 as the source for +5V. This wire is RED in my examples.
6.		Connect EPROM pin 2 (A12) to jumper location E4 (A14). This wire is pink in my examples.
7.		Connect jumper location E12 to ground. I use the large ground trace closest to E12. That will connect EPROM CE to ground. This wire is BLACK in my examples.
8.		Connect jumper positions E9 and E13A. That will connect EPROM A11 to CPU A11. This wire is green in my examples. NOTE: There is an error on the Bally schematic which shows jumper position E13 connected in common with E13A. This is an error and E13A will need to be used for this step.
9.		Connect jumper position E11 to the side of resistor R14 closest to the EPROM socket. That will connect EPROM OE to the output of the gate at U17A. That is an enable that combines CPU A12, VMA and phase 2 of the clock creating an enable that we can use for our EPROM. We could also use jumper location E35 but R14 is closer and makes for a cleaner installation, in my opinion. This wire is yellow in my examples.

Bally -35 2764 EPROM Conversion

3.20.5 Bally -17 And Stern MPU-100 2764 EPROM Conversion

These instructions will convert a Bally -17 or Stern MPU-100 MPU to use a single 2764 EPROM. Colors in the table will match the wire colors in the example photos.

Bally -17 And Stern MPU-100 - 2764 EPROM Conversion Instructions
1.		Remove any PROMs or EPROMs from U1, U2, U3, U4, U5 and U6.
2.		Bend out pins 1, 2, 20, 23, 27, and 28 on a 28 pin EPROM socket so we can solder wires to the pins and install it in socket U2 on the MPU. Pin 26 of the EPROM is not connected. I usually remove this pin from the socket but you can just bend it out and not connect anything to it.
3.		Ensure that there are no jumpers connected to E3, E4, and E8.
4.		Connect EPROM socket pins 1, 27 and 28 to +5V. I chose to use pin 24 of U3 as the source for +5V. This wire is RED in my examples.
5.		Next we need to connect EPROM A12 (pin 2) to CPU A14 (pin 24 of U9). The problem is that there are no jumper locations on the -17 and MPU-100 that are connected to A14 so we have to connect directly to pin 24 of the Motorola 6800 (U9). One option is to run the wire over the top of the board to the back (solder side) but I wanted to make my conversions look as clean as possible so I use pin 20 of U3 as a through hole to get to the other side of the board. So we connect pin 2 of the EPROM to pin 20 of U3 on the components side of the board then connect pin 20 of U3 to pin 24 of U9 on the solder side of the board. This makes for a clean looking conversion on the components side of the MPU. If you're going to use this method you need to ensure that there are no jumpers connected to E8. This wire is pink in my examples.
6.		Connect EPROM pin 20 (CE) to ground. I like to use the large ground trace closest to the EPROM socket. This wire is black in my examples.
7.		Connect jumper E3 to the side of resistor R14 closest to the EPROM socket. That will connect EPROM OE to the output of the gate at U17A. That is an enable that combines CPU A12, VMA and phase 2 of the clock creating an enable that we can use for our EPROM.
8.		Connect EPROM pin 23 to jumper location E4. That will connect EPROM A11 to CPU A11. This wire is green in my examples.

Bally -17 and Stern MPU-100 2764 EPROM Conversion

3.20.6 Stern MPU-200 2764 EPROM Conversion

These instructions will convert a Stern MPU-200 to use a single 2764 EPROM. Colors in the table will match the wire colors in the example photos.

NOTE: You may need to first convert your board to use two 2732 EPROMs before applying this conversion. If you leave the board configured for another rom setup; you may note the board will not flash the diag LED.

Stern MPU-200 - 2764 EPROM Conversion Instructions
1.		Remove any PROMs or EPROMs from U1, U2, U3, U4, U5 and U6.
2.		Bend out pins 1, 27, and 28 on a 28 pin EPROM socket so we can solder wires to the pins and install it in socket U2 on the MPU. Pin 26 of the EPROM is not connected. I usually remove this pin from the socket but you can just bend it out and not connect anything to it.
3.		Ensure that there are no jumpers connected to E2, E4, E5, E6, E10, E17, and E18.
4.		Connect EPROM socket pins 1, 27 and 28 to +5V. I chose to use pin 24 of U3 as the source for +5V. This wire is RED in my examples.
5.		Connect EPROM pin 2 to jumper location E10. This wire is pink in my examples.
6.		Connect jumper location E5 to E4.
7.		Connect jumper location E17 to E18.
8.		Connect jumper location E2 to E6

Stern MPU-200 2764 EPROM Conversion

3.20.7 Bally/Stern ROM Memory Map

ROM images based on 2732 EPROMs are available on the net for all Bally and Stern machines so I'll give an example of the ROM memory map using these as the example. This is important to consider when doing single EPROM conversions because you will need to create a custom ROM image from original game code.

ROM image	Memory Location (Hex)	Memory Location (Decimal)
U2 First half:	$1000-$17FF	(Decimal: 4096-6143)
U2 Second half:	$5000-$57FF	(Decimal: 20480-22527)
U6 First half:	$1800-$1FFF	(Decimal: 6144-8191)
U6 Second half:	$5800-$5FFF	(Decimal: 22528-24575)

3.20.8 Creating A 2764 ROM Image From 2732/2532 ROM files

This is one way to create a 2764 EPROM image.

1.	Download the game code. Most should be available from ipdb.org.
2.	Download Oliver's Vector home ROM files here. The archive will contain fsp.exe which we will use below to split the ROM images in half.
3.	Open a command (DOS) prompt and navigate to the directory where you unzipped the Vector home ROM file downloaded above. You will also want to have your 2732 game code images in this directory. What we are going to do is split the ROM images in half creating 4 new files. Here is the command syntax: fsp U2_2732_image.bin U2_split fsp U6_2732_image.bin U6_split Where U2_2732_image.bin and U6_2732_image.bin are the names of the U2 and U6 ROM images and U2_split and U6_split are the prefixes for the output files. We should now have files named U2_split-0, U2_split-1, U6_split-0 and U6_split-1.
4.	Now we can issue this command to create our image: copy /b U2_split-0 + U6_split-0 + U2_split-1 + U6_split-1 2764_ROM_Image.bin The command above must be entered as one string. This will create a file called 2764_ROM_Image.bin. Burn that to your EPROM and you're ready to go!