Gottlieb System 80

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1 Introduction

Gottlieb System 80 Board Set - 1st Generation

Gottlieb's second generation of solid state pinballs is System 80. Capabilities were increased in terms of controllable lamps, solenoids, gameplay, and sound. No longer tied to an EM-esque platform, Gottlieb started to introduce games with more unconventional asymmetric playfields. System 80 marked a foray into double and triple level playfields, speech, and multiball. Unfortunately, it also represented a step backwards in reliability, with battery corrosion, connectors, and bad grounding plaguing the design.

Once a system 80 game has been methodically gone through with board design grounding flaws and connectors corrected, they are just as reliable as any of their contemporaries.

Gottlieb System 80 Board Set - 2nd Generation

Gottlieb System 80A Board Set

Gottlieb System 80B Board Set - Early

Gottlieb System 80B Board Set - Typical

2 Games

2.1 System 80 1st Generation

Title	Date of Release	Production#	Model #	Sound	Notes
The Amazing Spiderman	05-1980	7625	653	Sound only
Panthera	06-1980	5220	652	Sound only
Circus	06-1980	1700	654	Sound only	Ultra Widebody
Counterforce	06-1980	3870	656	Sound only
Star Race	08-1980	870	657	Sound only	Ultra Widebody

2.2 System 80 2nd Generation

Title	Date of Release	Production#	Model #	Sound	Notes
James Bond	10-1980	3625	658	Sound only
Time Line	12-1980	3167	659	Sound only
Force II	12-1981	2000	661	Sound only
Pink Panther	03-1981	2840	664	Sound only
Mars God of War	03-1981	5240	666	Sound & Speech	First Gottlieb with speech, lane change, and multi-ball
Volcano	09-1981	3655	667	Sound & Speech
Black Hole	10-1981	8774	668	Sound & Speech	First Gottlieb with 2-Level playing area, Export games used sound only board
Haunted House	06-1982	6835	669	Sound only	First game with 3-Level playing area, Sound only, but used sound & speech board w/o the speech chip installed
Eclipse	1982	193	671	Sound only	Production game and available as a kit for James Bond 007

2.3 System 80a

Title	Date of Release	Production#	Model #	Sound	Notes
Devil's Dare	08-1982	3832	670	Sound & Speech	Export games may have used the sound only board - someone please confirm
Caveman	09-1982	1800	PV810	Sound & Speech	Pinball / Video game hybrid
Rocky	09-1982	1504	672	Sound & Speech
Spirit	11-1982	1230	673	Sound only	Sound only, but used sound & speech board
Punk!	12-1982	959	674	Sound only	Sound only, but used sound & speech board
Striker	11-1982	910	675	Sound only	Sound only, but used sound & speech board
Krull	02-1983	10	676	Unknown
Goin' Nuts	02-1983	10	682	Unknown
Q*bert's Quest	03-1983	884	677	Sound & Speech
Super Orbit	05-1983	2100	680	Sound Only	Sound only, but uses the less populated sound & speech board
Royal Flush Deluxe	06-1983	2000	681	Sound Only	Sound only, but uses the less populated sound & speech board
Amazon Hunt	09-1983	1515	684	Sound Only or Sound Only	Sound only, but uses the less populated sound & speech board. Later production games used the sound only piggyback sound board
Rack 'Em Up!	11-1983	1762	685	Sound Only
Ready... Aim... Fire!	11-1983	390	686	Sound Only
Jacks to Open	05-1984	2350	687	Sound Only
Alien Star	06-1984	1065	689	Sound Only	689A Denotes a revision in the ROM code
The Games	08-1984	1768	691	Sound Only
Touchdown	10-1984	711	688	Sound Only
El Dorado City of Gold	09-1984	905	692	Sound Only
Ice Fever	02-1985	1585	695	Sound Only

2.4 System 80b

Title	Date of Release	Production#	Model #	Sound	Notes
Chicago Cubs Triple Play	05-1985	~1365	696	Sound Only
Bounty Hunter	07-1985	1220	694	Sound Only
Tag Team Pinball	09-1985	1220	698	Sound Only
Rock	10-1985	1875	697	Sound Only
Raven	03-1986	3550	702	Sound Only
Rock Encore	04-1986	245	704	Sound Only	Production game using same playfield art as Rock, but mainly available as a conversion kit for Rock
Hollywood Heat	06-1986	3400	703	Sound Only
Genesis	09-1986	3500	705	Sound Only
Gold Wings	10-1986	3260	707	Sound Only
Spring Break	04-1987	3550	706	Sound Only
Monte Carlo	02-1987	4315	708	Sound Only
Arena	06-1987	3099	709	Sound Only
Victory	10-1987	3315	710	Sound & Speech
Diamond Lady	02-1988	2700	711	Unknown
TX Sector	03-1988	2336	712	Sound & Speech
Robo-War	04-1988	2130	714	Unknown
Excalibur	11-1988	1710	715	Unknown
Bad Girls	11-1988	2500	717	Sound & Speech
Big House	04-1989	1977	713	Sound & Speech
Hot Shots	04-1989	2342	718	Sound & Speech
Bone Busters Inc.	08-1989	2000	719	Sound & Speech	Used 3 sound boards

Game date of release, production numbers, and model number provided by the Internet Pinball Database - http://www.ipdb.org

3 Technical Info

3.1 System 80 / 80A / 80B Board Set

3.3 The Wiring Color Code

Unlike every other pinball manufacturer, which adopted a two-color wiring code system, Gottlieb used three colors. Most wiring in a Gottlieb game used a white base color, which is the wire's insulation color, and three "striped" traces on each wire. I state most cases, because there are some wires which only used two colors - the green insulated ground lines which have a single yellow trace, or only one color - the white ground wires used in System 80B games with no trace at all. Below is the Gottlieb color chart.

#	Color
0	Black
1	Brown
2	Red
3	Orange
4	Yellow
5	Green
6	Blue
7	Purple
8	Gray
9	White

Does the color chart look familiar? Well, if you have an electronics background, it should. The Gottlieb wire code system is the same as the resistor color coding system.

Here are some examples of the color coding system. The color wire code for switch strobe line 0 is 400. 400 would be a white insulated wire with a yellow trace and two black traces, or commonly referred to as a yellow-black-black wire. The ground lines in early System 80 games are code 54. 54 would be a green insulated wire with one yellow trace.

There is one word of caution, which should be pointed out. If the connections on A1J2 and A1J3 are being replaced, there are wire colors on these connections which are very similar. Although each wire is located on a different housing, please proceed with caution, as it can be difficult to see all three traces without spinning the wire around. The wires which come to mind are 344 and 677 on A1J2, and 433 and 766 on A1J3.

3.4 Connector Designations

All Gottlieb 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 or an inline wire junction, and the suffix is the connection on the board or a sequential wire junction number. When referencing a specific connector pin within a housing, a dash follows the connection number. For example, the connector pin for the slam switch signal on the CPU board is A1J5-10. The coin door connection used on Devil's Dare is A15P1 and A15J1 - the connector pin for switch return 7 on the coin door is A15J1-8.

The following boards are assigned the same numbers throughout the System 80 / 80A / 80B platforms.

• CPU Board - A1
• Power Supply - A2
• Driver Board - A3
• Sound Board - A6
• Pop Bumper Driver Boards - A8
• Reset Board - A24

There are several other board designations used, however, they change from game to game.

3.5 Switch Matrix

The Gottlieb System 80 / 80A / 80B switch matrix consists of a maximum of 64 switches. There are a total of 8 switch strobes and 8 switch returns. However, not every switch in the matrix is used on every System 80 game.

Just like the System 1 switch numbering system, the System 80 switch numbers have a similar naming convention. Except, the System 80 switch numbering system is the opposite of System 1. If you are accustomed to working on System 1 games, pay close attention. With Gottlieb System 80 switches the first number of the switch is its strobe number, while the second number is switch's return number. An example would be switch 54. Switch 54 is located on strobe 5 and return 4 of the switch matrix.

	Strobe 0 (A1J6-1 / A1J5-2)	Strobe 1 (A1J6-2 / A1J5-3)	Strobe 2 (A1J6-3 / A1J5-4)	Strobe 3 (A1J6-4 / A1J5-5)	Strobe 4 (A1J6-5 / A1J5-6)	Strobe 5 (A1J6-6 / A1J5-7)	Strobe 6 (A1J6-7)	Strobe 7 (A1J6-8 / A1J5-9)
Return 0 (A1J6-10)	00	10	20	30	40	50	60	70
Return 1 (A1J6-11)	01	11	21	31	41	51	61	71
Return 2 (A1J6-12)	02	12	22	32	42	52	62	72
Return 3 (A1J6-13)	03	13	26	33	43	53	63	73
Return 4 (A1J6-14)	04	14	24	34	44	54	64	74
Return 5 (A1J6-15)	05	15	25	35	45	55	65	75
Return 6 (A1J6-16 / A1J5-8)	06	16	26	36	46	56	66	76
Return 7 (A1J6-17 / A1J5-1)	07	17	27	37	47	57	67	77

3.5.1 The "Missing" Gottlieb System 80 Switches

With the Gottlieb System 80 series of games, there are some switch assignments that are designated the same throughout the System 80, 80A, and 80B platforms. These switches are typically not listed in the switch matrix portion of the manual. You have to review the cabinet schematics, and decipher what switches use what return and strobe. However, it appears that Gottlieb / Premier changed this section of the schematic starting with Excalibur or Bad Girls by no longer listing the strobes for these switches. So, below are the "missing" switch assignments for any Sys80B. All the info applies for Sys80 and Sys80A, except the two advance buttons, which weren't used prior to Sys80B.
06 - left advance button (Sys80B only)
07 - play / test switch
16 - right advance button (Sys80B only)
17 - left coin switch
27 - right coin switch
37 - center coin switch
47 - replay button
57 - plumb bob and ball roll tilts (these have the same switch assignment as the playfield tilt switch)

Black Hole is one exception. The switch assigned for the tilt on Black Hole is 26.

Note: The coin door slam switch is not part of the switch matrix.

3.5.2 Setting up a Game for Free Play

Early Gottileb solid state pinball machines, prior to 1990, did not have a free play option available within the game settings. With this simple modification, a game can be set up for free play. First, identify the diode strip in the bottom of the cabinet. Once the diode strip is found, locate the credit button and coin switch strobe line wires. The wires will be located on the left of the diode strip - the non-banded side of the diodes. Below is a list of the wires.

Credit button wire - Green-Yellow-Yellow
Left coin switch wire - Green-Brown-Brown
Center coin switch wire - Green-Orange-Orange
Right coin switch wire - Green-Red-Red

Gottlieb System 80 Transformer Board

Solder a small lead wire from the credit button wire to any of the coin switch wires. Make certain that the diode, credit button wire, and coin switch wire are still soldered securely to the diode strip terminal when finished. If soldering is not an option, use a small alligator clip test lead. Now, when the credit button is pressed, a credit will be incremented and decremented. A game can be easily started without the need to open the coin door to trip the coin switches anymore.

Please note that this modification does not apply to Gottlieb System 80A and System 80B machines. System 80A and 80B machines use diode boards with edge connections, which are typically located on the cabinet wall near the left flipper cabinet switch. In my experience, jumpering the diodes on System 80A and 80B games do not give the intended free play results of jumpered System 80 diodes. I attribute this to the System 80A and 80B software reading the switch matrix differently.

3.6 Power Supply

3.6.1 System 80 / 80A Power Supply

System 80 / 80A Power Supply

The System 80 / 80A power supply is very similar to the System 1 power supply, where as the circuit board is secured to a large "hot plate" heat sink. This style power supply is used for all System 80 and 80A games from Spiderman to Ice Fever, and is the source of the following:

• +5 VDC logic power
• +8 VDC offset voltage needed for the displays
• +60 VDC for the 6 or 7 digit displays
• +42 VDC for the status display
• Ground from earth ground located on the transformer panel
  

Unlike the System 1 power supply, the +5 VDC logic power is no longer rectified and filtered on the power supply itself. This process is now handled by a bridge rectifier and a large filtering capacitor located on the transformer panel. The System 80 power still employs a crowbar circuit [1] for the logic power, which is very beneficial.

System 80 / 80A Power Supply - Showing the Large Heat Sink

Although these power supplies are fairly reliable, there are some drawbacks to the design. By incorporating a large heat sink for the PMD10K40 / 2N6059 TO-3 transistor on the board, a lot of heat is dissipated throughout the whole board. This in turn will limit the life expectancy of the other electronic components on the board. Equally, the heat sink must be removed in order to perform component level repairs to the board.

3.6.2 System 80 / 80A Sound & Speech Power Supply

A sound & speech board (S&S) is used starting with Mars God of War (MGOW). Because of the voltages needed to drive some of the components on the S&S board, this secondary power supply is added to the power train. The voltages generated from this board are:

• +12 VDC used for the analog inverters and voice synthesizer chip
• -12 VDC used for the analog inverters
• +30 VDC used for amplification

~~ need pic inserted J.P.

There are two different variations of this power supply. The first style is used only with MGOW, and is not a printed circuit board (PCB). The electronic components were screwed to a block of wood, which is located on the left wall of the lower cabinet. Conducting tests and repairs to this style power supply can be awkward and difficult.

System 80 / 80A Sound & Speech Power Supply

Starting with Volcano, the S&S power supply is now on a circuit board, which is located in the head of the game with the other circuit boards. Even though each style of S&S power supply uses different components for the generation of +12 VDC, the end result is the same. The S&S power supply was no longer used when Gottlieb went a step backwards, and installed the System 80A sounds only board with the piggyback board. This change occurred during the run of Amazon Hunt.

3.6.3 System 80B Power Supplies

Starting with Chicago Cubs, the Gottlieb power train went through a bit of a face lift. The System 80B platform uses two separate boards to supply power. This design change is mainly due to the single display board, which rectifies the high voltage on the board itself.

System 80B +5 VDC Power Supply

The small power supply with the finned heat sink is only used to generate +5 VDC for logic power. Although, removing the heat sink is not necessary to work on the board, this power supply has its own set of issues. First, it does not have a crow bar circuit. If the LM338K voltage regulator fails, and fails whereas the voltage increases drastically, it can destroy electronic components on the other circuit boards. Secondly, it's not as bad, but heat is still dissipated throughout the board. Third, the adjustable potentiometer (pot) on the power supply is prone to failure, due to dirt, dust, and contaminants. Finally, it is typical for the header pins on the input and output of the board to develop cracked solder joints. The two latter problems can easily be overcome, and will be addressed in the Power Problems section below.

System 80B Auxiliary Power Supply

Starting with Rock, the second power supply is added, and is referred to as the auxiliary power supply. The primary functions of this board is used to power the sound board, and amplify the audio output. A breakdown of the voltages supplied by the auxiliary power supply are as follows:

• -12 VDC
• +12 VDC

3.7 CPU Board

Gottlieb System 80 CPU Board

The System 80 CPU board is a 6502 based microprocessor system. The 6502 microprocessor (the very same one used in the first Apple computer) executes the basic operating system contained in the masked ROMs at U2/U3. The game code "personality" augments the basic operating system PROM(s) and is also contained in masked ROMs (the OEM ROMs were masked) at positions PROM1 and (possibly) PROM2. "Scratchpad" memory is added via a 5101 256x4 bit CMOS memory at Z5. Control of peripheral devices (in this case lamps, solenoids, switches and sound) is accomplished via three 6532 RIOTs (RAM-I/O-Timer) at U4, U5, and U6. Each RIOT in turn controls it's own "subsystem" to drive these devices.

• Reset section

• Switch matrix

• Solenoids and Lamps

• Displays

There are four generations of the System 80 board. All of the CPU boards can be easily identified by their revision numbers notated just below the operator adjustable dip switches.

3.7.1 1st Generation CPU Board

System 80 CPU Board - 1st Generation

The first generation CPU is used in the first 5 System 80 games, and is marked with the following:

• ASSY PB03-D100-001
• DET PB03-D102-001
• REV B ASSY.

This board uses two masked PROM chips for the game code. The chips are typically labeled with the three digit game model number followed by /1 or /2, designating the game PROM position. An example of this naming convention is shown in the pic to the left. 652/1X and 652/2X are game PROM 1 and PROM 2 for Panthera. The "X" in this case designates a code revision. The masked ROMs at position U2 and U3 are not socketed on this board.
With some simple modifications, this board is upward compatible to use a single 2716 EPROM placed in the PROM 1 socket of the board. With the change of U2 and U3, this board can be used in System 80A games. The board could potentially be used in a System 80B game with many modifications, and the addition of a daughter board, however, it is not recommended.

3.7.2 2nd Generation CPU Board

++ need pic ++
The second generation CPU is used in some System 80 games, and is marked with the following:

• ASSY PB03-D100-??? - check boards for the suffix
• DETAIL PB03-D107-001

This board uses a single 2716 EPROM chip for the game code located at the PROM 1 socket position. The chips are typically labeled with the three digit game model number. Occasionally, the chip's game number label will be followed by /1, /2, /3, or even /4. In this case, the number following the slash is the code revision number. An example of this naming convention is 658 /2, which is a game PROM for James Bond - code revision 2. The masked ROMs at position U2 and U3 are not socketed on this board either.
With the change of U2 and U3, this board can be used in System 80A games. The board could potentially be used in a System 80B game with many modifications, and the addition of a daughter board, however, it again is not recommended. The second generation CPU is backward compatible, provided a doubled up, single game PROM is used at the PROM 1 position.

3.7.3 3rd Generation CPU Board

System 80 CPU Board - 3rd Generation

The third generation CPU is used in some System 80 games, and is marked with the following:

• ASSY PB03-D100-011
• DETAIL PB03-D107-003

This board is essentially the same as the second generation board, except an eyelet ground trace was placed just above Z33 on the board. This ground trace was never used. All information which applies to the second generation CPU board, applies to this board. The third generation CPU is backward compatible, provided the same is done it as the 2nd generation board.

3.7.4 4th Generation CPU Board (System 80A)

System 80A CPU Board

The fourth generation CPU is used in all System 80A games, and is marked with the following:

• D 20869

This board is the same as the third generation board, except the U2 and U3 masked ROM chips have different code, and are now socketed. The PROM 2 socket is no longer populated on the board. The fourth generation CPU is backward compatible, provided the System 80 ROM code is installed at U2 and U3. If used on a game with the 1st generation CPU, the game code must be doubled up on a 2716 EPROM, and installed at the PROM 1 position. This board is forward compatible with System 80B, provided all of the above outlined modifications are performed. Out of all the System 80 CPU boards, this is the most compatible with System 80B, due to using the same base circuit board.

3.7.5 5th Generation CPU Board (System 80B)

System 80B CPU Board

The fifth generation CPU is used in all System 80B games, and is marked with the following:

• D 20869

Even though,the base circuit board is identical to the fourth generation CPU board, it's being named the fifth generation board, due to all of the major changes. The U2 and U3 masked ROM and sockets have been replaced with a piggyback daughter board mounted in the U3 position. The daughter board uses a 2764 EPROM. Most of the related display segment and digit chips are no longer populated. This is due to the single display board handling these functions on its own board. The missing chips once used for the displays are Z19, Z21, Z22, Z23, Z24, and Z25. Equally, jumpers have been placed where Z19 and Z21 once resided. The fifth generation CPU is backward compatible, after the daughter board has been removed, and the missing display chips populated.

Any of the Gottlieb System 80 / 80A / 80B CPU boards are compatible cross platform. It's just matter of how much work must be done to modify each board.

3.8 Driver Board

The System 80A / 80B Driver Board

The System 80 Driver board is responsible for all controlled lamps, relays, and all solenoids in the game. The CPU controls the driver board operation via a simple interface between A1J4 on the CPU and A3J1 on the driver board. Although the driver board went through some minor changes over the years, the same board can be adapted for all of the System 80 platforms.

To control the games' total of 51 lamps, the interface provides "device select" signals for each of the 74175s (Quad-D Flip-Flops) on the driver board, and 4 "bits" of data that is loaded (or "clocked") into a particular 74175 via the aforementioned device selects. Each lamp is driven discretely by a particular output of a particular 74175, which in turn drives an MPS-A13 or MPS-U45 transistor, (NDS-U45 transistors were used in place of MPS-U45s in some cases). Gottlieb did not implement a "lamp matrix" as some other manufacturers did.

It is noteworthy that there are some dedicated lamp transistors, which control specific game relays across the System 80 / 80A platforms. Relays such as the game over, tilt, and coin lockout relays are controlled by Q1, Q2, and Q3 respectively. The tilt and game over relays use the same designation for the System 80B platform, however, the use of a coin lockout relay was abandoned by this time. One neat feature of the driver board circuitry is that lamp "n" is driven by transistor Q"n+1". i.e. L12 is driven by Q13.

Driver Board with Coin Counter Transistors Highlighted

To control the games' solenoids, the driver board uses signals directly from the CPU to enable transistors on the driver board which turn on up to 9 solenoids. For solenoid control, the driver board uses MPS-U45, 2N3055, and 2N6043 transistors. Starting and ending with the System 80 platform, (games from Spiderman to Haunted House), three transistors were reserved to drive optional mechanical coin counters. These mechanical coin counter solenoids and associated transistors are: solenoid 3 (Q54), 4 (Q55), and 7 (Q56). Starting with the System 80A platform, (Devil's Dare), these transistors were no longer reserved for coin counters, and were used for other functions. Equally, the 3 diodes associated with these 3 transistors were changed to 3 zero ohm jumpers.

The games' sound signals (S1, S2, S4, S8) also pass through the driver board at Z13, a 7404 Hex Inverter. See below for S16 and S32.

Repurposed Driver Board Circuits:

A Typical Remote Transistor Mounted Under the Playfield

Since quite a few System 80 games employ more than 9 solenoids, and since the original driver board design will drive a maximum of 9 solenoids, Gottlieb repurposed some lamp outputs to drive "under-playfield transistors" which drive additional solenoids.

A Typical Transistor Driver Board

Once playfields became littered with numerous "under-playfield transistors", Gottlieb opted to merge some of these transistors into a transistor driver board. The transistor driver board started to appear on Gottlieb games nearly midway through the System 80B platform, with the game Victory.

The sound S16 and S32 signals are also repurposed lamp outputs. For instance, Haunted House and Black Hole both repurpose L9 to S16. Robo-War repurposes lamp 4 to S16. Note that S16 is not consistently implemented across the System 80 family. Note also that references to the usage of S32 are difficult to find.

3.9 Sound Boards

Gottlieb uses different sound boards throughout the course of all System 80 platforms. Several of the sound boards cross platforms too. Out of all of the sound boards used, there is really only about three base units total with variations made to each one.

3.9.1 Sounds Only Board

Gottlieb System 80 Sound Board (Sounds only)

The first System 80 sound board is capable of sound only. Based on the 6503 CPU architecture, this sound board is very similar to the System 1 Multi-Mode sound board. However, there are a couple of differences between the two boards. First, the +12VDC is no longer rectifed on the sound board. The +12VDC power comes from the power supply. Secondly, the +5VDC is no longer regulated on the sound board. The System 80 sound receives +5VDC from the power supply also. Finally, the pin outs for the System 1 sound board and the System 80 sound board are completely different. Even though either board will plug into either platform, DO NOT PLUG A SYSTEM 1 SOUND BOARD INTO A SYSTEM 80 GAME AND VICE VERSA!!! If you do, bad stuff will happen. Unfortunately, there are two chips (6503 and 6530) on this style of board which are very difficult to source.

3.9.2 Sound & Speech Board

Gottlieb System 80 / 80A Sound & Speech Board

Starting with Mars God of War, the second System 80 sound board has the the capability of speech. Ironically, this board is commonly referred to as the "sound and speech board", and was brought over from the Gottlieb video game division at the time. Fortunately, Gottlieb chose the 6502 CPU architecture just like the CPU board. There is a 6532 RIOT used also. The downside to this board is the now rare LM379S amp and SC-01 phoneme speech chip are both difficult to acquire.

3.9.3 Sound Only Board

Gottlieb System 80 / 80A Sound Board w/ MA-483 Piggyback Board (replaces LM379S amp)

To reduce costs, Gottlieb abandoned the speech option, and went a step backwards with a board generating sounds only. In doing so, they used the same base board as the sound and speech board, however it was populated with less components. Equally, when the LM379S amp became too costly, a piggyback board (as shown in the picture) with a TDA2002 amplifier and associated necessary electronics.

3.9.4 Sound Only Board with Piggyback

Gottlieb System 80A / 80B Sound Board w/ MA-488 Piggyback Board (Sounds only)

To reduce costs even more, Gottlieb started using a modified sound only board, which was first used with Spiderman. The board was modified with a piggyback board housing an EPROM.

3.9.5 System 80B Sound Board

Gottlieb System 80B MA-766 Sound Board

And now for something completely different. Well, not really. This sound board hit the scene with Rock, but a similar design was already used prior by the Gottlieb video game division when it existed. It is based on the 6502 CPU architecture, but uses two 6502s instead of one.

3.9.6 System 80B Sound Board

Gottlieb System 80B MA-886 Sound Board

The MA-866 board is essentially the same as the previous sound board, except it uses .156" header pins instead of edge connectors for inputs / outputs.

3.11 Displays

3.11.1 System 80 - 6 Digit Displays

3.11.2 System 80A - 7 Digit Displays

3.12 Bookkeeping & Diagnostics

To enter the bookkeeping/diagnostic mode, open the coin door and press the micro switch. (Note this switch has no credit function) The credit display will show "00". Pressing the self test switch again will advance it to the next step in the diagnostics. You can skip the bookkeeping functions and go directly to diagnostic step 16 by pressing the credit/start button right after entering the bookkeeping/diagnostic mode.

Gottlieb System 80 Coin Door Test Button Highlighted

Bookkeeping (System80 only!)
1 - Coins thru left chute
2 - Coins thru right chute
3 - Coins thru center chute
4 - Total plays
5 - Total replays
6 - Game percentage
7 - Extra ball
8 - Total tilts
9 - Total slam tilts
10 - Number of times the HSTD has been beaten
11 - First high score level
12 - Second high score level
13 - Third high score level
14 - High score to date score
15 - Average game time

Diagnostics
Note: pressing the credit/start button during any of these tests restarts the test.
16 - Lamp test
17 - Coil test (will cycle and display coil number of coils used in the game. Coin counter coils, if installed, are excluded)
18 - Switch test. (99 = no fault) You can check switch numbers by pressing them on the playfield during this step.
19 - Display test. The displays will cycle through each digit
20 - Memory test. (99 = no fault)

You can trigger the slam switch, tilt switch or wait 60 seconds to reset the CPU back to play mode. (This is why my slam switch is still functional!)

4 Problems and Solutions

4.2 Power Problems

4.2.1 Replacing the Orange Filtering Capacitor

A worn out original 6800uf/25V Gottlieb filter capacitor

If your System 80 or early System 80A game still has the original, orange 12VDC filtering capacitor in the cabinet bottom, you should replace it. It's nearly 30 years old, has served the game well for a long time, and deserves a rest. Replace it with a new capacitor, valued from 6800uf to 12,000uf and at least 25V. Don't forget to acquire the right sized bracket to secure the cap to the bottom board.

4.2.2 Recommended Updates and Repairs for the System 80/80A Power Supply Board

The System 80 Power Supply board is a pretty tough bugger. Still, after years of steady operation, they do fail, and they require refurbishment.
The test point values are silk screened on the System 80 power supply board. They are +5VDC, +8VDC, +42VDC, and +60VDC. Ground, or "common" is also labeled.
Given that the parts to refurbish the power supply are cheap and readily available, and taking the power supply apart is a bit of a pain, a good strategy is to replace everything in one shot. Whether the parts need replaced or not, try to avoid disassembling the power supply more than once.

Parts you will need are:

1. .156 male header pins without friction lock, 9-pin, 7-pin, 6-pin, or break to size.
2. 500 ohm resistor trim pot. A quality sealed one like the one pictured is advised.
3. 3 inches of 18 gauge wire
4. 47uf, 100V axial capacitor
5. 680 ohm, 1/2 watt resistor (replacement for R10)
6. 12K ohm, 1/2 watt resistor (R3)
7. 1N4738 8.2V 1 watt zener diode (CR7)
8. 1N4746 18V 1 watt zener diode (CR6)
9. LM723 voltage regulator and 14-pin socket (optional if the 5V section is operational)
10. 2N6057 or 2N6059 Darlington transistor (Q3, optional if the 5V section is operational)
11. heat sink compound (optional as required)
12. TO-3 mica insulator or heat sink gasket (optional as required)
13. TO-3 transistor spacer (optional as required)
14. 2N5550 or 2N5551 transistor (Q2, optional)
15. Green LEDs (optional...use if you want to identify the board as having been reworked)

Procedure:

1. Remove the 4 screws that fasten the PCB to the cold plate (heat sink).
2. Remove the 2 screws that fasten the back mounted transistor Q3 to the PCB and cold plate.
3. Use your favorite solder removal tool to remove the solder from the legs of Q3 that extend through the PCB. This is the toughest part of the job. If the board had been really hacked, you may need two irons and a friend to accomplish this.
4. Once the cold plate and Q3 have been removed, set those parts to the side.
5. Replace parts on the PCB as recommended and advised by the particular failure.
6. On the solder side of the PCB, solder a 3" wire from the ground trace to the screw mount, as shown in the picture below.
7. When replacing the original round header pins with new square header pins, you may have to enlarge the holes slightly using a pick as shown in the picture below. Key pins must be removed prior to installation as the PCB has no holes at the key pin position.
8. Recheck all of your work.
9. Sand the black insulating coating from the top/right screw hole on the front of the cold plate, as shown in the picture below. The insulating coating is very tough. A drum sander attachment on a Dremel works very well for this. To ensure you've sanded enough, use your meter to "buzz" between screw holes. You will use this screw hole later to tie the ground from each PCB together.
10. Install Q3 (note that it will only install one way) onto the cold plate using the transistor spacer, mica insulator, and heat sink compound.
11. Mate the two halves of the power supply together and reinstall the two screws which secure Q3.
12. Solder the leads of Q3 to it's through-holes.
13. To ensure continuity at each leg's solder joint, "buzz" the connection between the left leg of Q3 and the top leg of R9.
14. Also "buzz" the connection between the right leg of Q3 and the bottom leg of R11.
15. Install the remaining 4 screws around the perimeter of the power supply board.
16. Lastly, ensure there is NO continuity between Q3 and the cold plate, as shown in the picture below. This is an essential step to ensure proper operation.

• System 80/80A Power Supply Repair
• 

  Parts Required
• 

  Front Side, Parts Removed and Board Cleaned Up
• 

  Back Side, Parts Removed
• 

  Enlarging Header Pin Holes
• 

  Parts Replaced, Front Side
• 

  Parts Replaced, Back Side
• 

  Strain Relief for R10
• 

  All Done
• 

  Ensuring no continuity between Q3 and the cold plate

Once fully assembled, reinstall the power supply into your game. Connect ONLY J1 (the lower 9-pin connector) at this time. Power your game on, looking for the two LEDs to light. If they do not light, you have rework to perform. Assuming that they do light, test each of the voltages that the power supply creates to ensure the correct power is being generated/regulated. Since the power is not "under load", each of the voltages may read 10% or so high. While measuring the 5V test point, adjust the 5V trim pot to about 5.1VDC.

That's it! You're done.
Note: once you connect the other boards to the power supply, the 5V may sag some. Measure the 5V across the electrolytic cap just to the right of the MPU power connector. Using the 5V trim pot, adjust the 5V power to between 5.0 and 5.1VDC.

4.3 MPU boot issues

There are a large and varied number of reasons that a System 80 MPU will fail to boot. Unfortunately, as has been said before, "this is not a Bally world". That is, unlike "classic" Bally and Stern MPUs the System 80 MPU provides absolutely no indication as to why it may have failed to boot.

Debugging a non-booting MPU is somewhat of an art.

Under construction...

1. Ensure your game is providing a solid 5VDC power source
2. Replace the orange electrolytic cap in the cabinet bottom if still original
3. Take the board to the bench
4. Examine the board for Alkaline damage. If present, clean up
5. Ensure the reset section of the board is working. Pin 40 of the 6502 should begin "low", then after about 1/2 second, transition to "high"
6. Check the clock signals at the 6502
7. Check the IRQ signal at the 6502
8. Check the R/W (read/write) signal at the 6502
9. Check the address and data lines to see if they are pulsing
10. Feel each of the masked ROM chips at U2 and U3 as well as the 6532 RIOT chips at U4, U5, and U6. If the IC is too hot to touch, it has probably failed and should be replaced.
11. Check each of the 74XX chips using the procedure "here".
12. If original game ROM(s), replacement with 2716 is advised.

4.3.1 Battery Leakage and Corrosion

Like most any other pinball machine manufactured, Gottlieb uses batteries to supply power to the non-volatile RAM memory. Certain game settings, high score thresholds (including high score to date), audit information, and bookkeeping information are all options which are saved when the game is powered off. And unless some kind soul, who worked on your machine before, either removed the battery and mounted it remotely away from circuit boards, or just plain removed the battery, there will be some variety of a 3.6v Nickel Cadmium (NiCad) rechargeable battery soldered onto your CPU board.

So, what's so bad about having a battery on the CPU board? Well, nothing really, unless it becomes forgotten, and most cases it does. While you let your pinball machine sit unplayed for weeks, months, or even years at a time, the battery remains perched on the circuit board like a ticking time bomb. I'm not saying the battery is going to blow up, although some replacement non-rechargeable batteries could overheat and / or explode if not correctly installed. The battery is like a ticking time bomb, because it is a threat to the overall health of the electronic components, traces, and connectors attached to your CPU board.

Now that I have your attention regarding the whole battery thing, let's talk about the battery, and what happens. . .WHEN GOOD BATTERIES GO BAD. It's not that some batteries were born on the wrong side of the tracks or anything. Any good battery can go bad without much warning. It takes time, but eventually you will find out that your battery has stepped over to the "dark side". That particular time is typically when you turn your game on, the lights come on, and that's it. The displays don't light up, the start up sounds don't resonant, and the silver ball stays in its comfy little home. Nada, nothing, no signs of anything resembling a fun game of pinball. UH-OH! So what happened? The pinball machine worked fine the last time you played it.

Well, while you were out having a good time and enjoying life, the poor, aged, neglected battery decided to wreak havoc all over the reset section, clock section, or possibly more regions on your CPU board. The CPU battery spewing its guts all over the place is akin to the batteries in the flashlight you haven't turned on since the last power outage over a year or two ago. You go to turn on the flashlight when you need it most, and find out there's something wrong. So being the curious type, you open the flashlight's battery compartment only to find some kind of funk leaking all over, or the batteries now look like they need a shave. The resolution to the flashlight scenario is pretty simple. Throw it away, and buy a new one. Your CPU board problem can be resolved the same way, except it will be a lot more costly, and is not recommended to just pitch it in the trash. If the battery damage to the CPU board is not overly extensive, attempt to repair it.

Typical Battery Found on a System 80 CPU Board

It's unfortunate, but every battery has a life expectancy. The only silver lining is that some of the Ni-Cad batteries installed on Gottlieb CPU boards can last longer than others. Probably the worst culprit of board destruction is the Data Sentry pack, and its associated knock-offs. This battery comes in a black rectangular plastic package.

Typical Battery Found on a System 80A / 80B CPU Board

Another battery pack style which looks very similar to the NiCad battery packs found in "old school" cordless phones. It is actually three small NiCad cells wrapped separately in an orange poly material, which is wrapped in a outer white poly material. These don't leak nearly as badly, but they still have the potential to fail.

Typical NiCad Battery Which was Replaced

The final common battery style is a what looks like an AA battery on steroids. This style is a fraction longer and fatter than an AA battery's physical form, and has two soldered leads on either end. If you find one of these, it means the battery was previously replaced. The good news is that this battery is newer than the original. However, the same results of battery seepage can occur. The only benefit of this type of battery is that it can be carefully cut (in most cases) from the board without removing the board from your game. This is a plus if no battery damage has occurred.

NiCad Battery Damage to a System 80A CPU Board
(Note: This is considered very mild damage!)

So what happens if you don't heed the above warnings, and the battery is allowed to remain on the board? Plain and simple - THE BATTERY WILL LEAK! It's only a matter of time. Equally, the path of destruction is uncertain. Batteries don't just leak - they release caustic, alkaline fumes. These fumes attack wherever there is copper, even tinned or soldered copper. The end results are:

• solder joints which become green or gray and crusty as opposed to a shiny silver
• connectors which are also now green / gray or potentially broken
• solder mask, the green covering the electronic traces, on the circuit board has either flaked off or is partially delaminating (lifting)
• insulated wire becomes less flexible and brittle
  
• sometimes the alkaline "cloud" in the game's backbox causes every board in the head to be affected.

Electronic components, related solder joints, circuit board traces, connectors, and even insulated wire will become unreliable and/or fail. In all cases, the effected components are less conductive.

If battery damage has occurred, the related parts must now be replaced. Attempting to remove soldered through components on the circuit board is now even more of a task. The green / gray dull solder does not transfer heat well. Battery damaged solder does not flow like clean solder. Also, crimped connectors are more difficult to remove from their housings, and have a tendency to break before they can be successfully pulled out.

After all the effected electronic components are removed, the board must be treated. This process starts by sanding the traces and solder pads until shiny copper is exposed. It is worth mentioning that a battery damaged board can be treated by bead blasting instead of sanding, however, most people do not have access to such a machine. After the copper areas of the board have been either sanded or bead blasted, an acidic bath of 50% vinegar and 50% (preferably distilled) water is applied to the board. A small brush like a toothbrush can be used to scrub the board's area. The purpose of introducing an acid to the effected area is to neutralize what the battery has left behind. The liquid and fumes from the battery are actually a base, not an acid. Next, rinse the area of the board with water. Once the board is clean, isopropyl alcohol (the higher the alcohol percentage the better) is applied to the same area to rinse away the acid bath, and hopefully dissipate any remaining water. Finally, the board is either blown dry or air dried. This may be a given, but DO NOT ATTEMPT TO APPLY POWER TO THE BOARD IF IT IS STILL WET! Most liquids are conductive to some extent. After the previous steps are performed, the task of installing the new components begins. If any traces or solder pads were damaged, see the Repairing Traces portion of this Wiki guide on to to fix them.

The point I'm trying to ultimately make is this. . . regardless of age, shape, or form, remove the battery from the CPU board, as soon as it realized that there is a battery on the board. If not, the board can be damaged, nonfunctional, and become more difficult to repair.

4.3.2 Relocating the battery from the MPU board

The first thing you should do to any System 80 MPU is remove the rechargeable NiCad battery from the MPU board. All batteries leak. It's simply a matter of when they will leak. A leaking battery will damaged your (sometimes irreplaceable) board.

There are at least four methods of relocating and/or replacing the battery on your System 80 MPU.

• You can remove the battery completely and not replace it. The 5101 memory will not persist from power-up to power-up and therefore, high scores, replay levels, and credits will be lost.

Remote Battery

• You can mount a remote battery pack that uses standard AA batteries (x3) to protect your board. You must also incorporate a blocking diode (1N4001, although a 1N4004 will work just as well) to prevent the game from attempting to charge the batteries. Install the blocking diode in series with the positive lead of the battery pack, with the band oriented toward the MPU.

Here a 5.5V, 1F Super Cap is used to retain 5101 memory for up to 30 days

• You can replace the battery with a 1F 5.5V "SuperCap". The capacitor will never leak, will charge during power-on cycles, and will retain 5101 memory for about 30 days.

• You may remotely mount a replacement NiCad battery in a location that, should it leak, damage to valuable circuit boards will not occur.
  

4.3.3 Repairing Alkaline Corrosion

A System 80 MPU with alkaline damage repaired/cleaned. Reset circuitry replaced with the much simpler Dallas Maxim 1811

If you find that the battery has leaked, alkaline damage can be cleaned up, traces repaired, and new components installed with kits available from several sources, including Great Plains Electronics.

An alternative to replacing a great many of the components is to use the Dallis/Maxim DS1811 reset generator. The DS1811-10 has a typical trip point of 4.35VDC. You may also use the Microchip Technology equivalent, part number MCP130-450DI/TO, available from Great Plains Electronics.

4.3.4 Slam Switch Modification

In order to test the CPU board on the test bench, a modification must be made to the CPU board to make the CPU think that the slam switch is closed. If the CPU thinks that the slam switch is not closed, the CPU will not complete the boot process, instead booting into a mode where the displays flicker all zeros at a very rapid rate. See the image here for a depiction of what you'll see.

Gottlieb designed the slam switch as a normally closed switch. That is, the switch must be closed for the machine to operate normally. When a brute kicks the machine, the slam switch will open from the inertial force on the weight attached to the switch, and the slam switch will open. Since the CPU is on the bench, we need a way to have this switch closed at all times to properly test the board.

Additionally, slam switches themselves fail. It's a good idea to implement this change as a preemptive fix for slam switch failures.

Slam Switch Mod

The slam switch can effectively be permanently closed by making a small solder bridge across two traces to the right of Z26 (which is on the lower right side of the CPU board). To permanently close the switch, remove the solder mask by scraping with a sharp knife or screwdriver. Create the solder bridge between the two now bare traces. This change will connect pin 13 of Z26 to ground, permanently closing the switch.

Alternative Slam Switch Mod

An alternate method of achieving the same results is to solder a clipped resistor leg across the bottom of capacitor (C30) and resistor (R20), both immediately to the left of Z26.

Keep in mind that the last 4 Gottlieb System 80B games were released with normally open slam switches. Do not perform the slam switch modification on these games. This includes the following games:

• Bad Girls
• Big House
• Hot Shots
• Bonebusters, Inc.
  

4.3.5 Connecting a logic probe to the MPU

A great place to source power for your logic probe while diagnosing the board is across the filter capacitor just to the right of connector J1. Connect the black lead of your logic probe to the negative (bottom) lead of the capacitor. Connect the red lead of your logic probe to the positive (top) lead of the capacitor. Take care to ensure that the clips don't short to adjacent components.

4.3.6 Using a PC Power Supply For Bench Testing

Future Update****This section works for now, but we can generalize bench power supply construction here: Building a flexible power supply for bench testing PCBs

The MPU board is much easier to work on if it is removed from the backbox and placed on the test bench. An AT-style PC power supply can be used to power the MPU board on the bench.

Obtain an old PC power supply. If you don't have an old computer laying around, head on off to the thrift store and pick one up. Remove the power supply from the case by unscrewing the appropriate screws. Be careful not to unscrew the power supply case itself.

Power Supply

Clip one of the connectors from the power supply wire bundle and clearly mark on the power supply box the value of each of the colored wires from the power supply. Typically, the yellow wire is 12V, red is 5V, and the black is ground. Strip insulation from the end of the red wire and the black wire as the System 80 MPU requires only 5V and ground to boot. Use alligator clips to connect 5v and ground to the appropriate J1 connection. I use larger alligator clips to make the connection easier.

J1 Connector

Mark connector J1 where the positive and negative (common) connection is for the five volts from the computer power supply. The ground connection is on the top of the connector, the 5V connection is on the bottom. The image shows A1J1 with the markings. I took the picture with the board still mounted in the machine. Connect the 5v supply with alligator clips to the positive connector on J1 and the black wire (ground) to the negative connector of J1. That's it! you're good to go!

4.4 Game resets

System 80 games sometimes exhibit "resets", especially when high power coils fire. Assuming you've updated the power supply grounds and reflowed or replaced the header pins on the Power Supply, there are a few typical causes for System 80 resets.

Gottlieb System 80A Filtering Capacitors

1. The 12VDC filter capacitor in the cabinet bottom which, if still original, should always be replaced. Originally, this was a 6800uf/25V capacitor. Replace with a 10-12,000uf/25V cap such as this one from Great Plains Electronics. The filtered 12VDC is regulated down to 5VDC on the power supply board. Note that some games have two of these capacitors (as shown).
2. The bridge rectifier that originates the 12VDC
3. Missing, broken, or failed coil diodes
4. Poor 5VDC power connections between the power supply and the MPU. The female connector on the MPU connects 5VDC to the MPU via molex crimp-on pins and a "double-wide" edge connector pad. Ground is connected in the same way. But you've done the ground mods, right?

4.5 Solenoid problems

Under Playfield Transistor, with Emitter, Base, and Collector Labeled

Under playfield transistors were originally 2N5875s or 2N5879s. I find the failure rate of the original transistors to be high. I guess 30 years is a long time for a transistor of that technology. Should one fail, you can replace it with it's beefier sibling, a 2N5884. An MJE2955 will work also.

The green/yellow wire (Gottlieb wire color code 54) is always connected to the tip of the transistor (collector) and leads to ground.
The "emitter" should be connected to the coil's lug that is also connected to the non-banded side of the coil diode (black-blue-blue in this picture).
The "base" should be connected to the drive wire from the driver board (brown-red-red in this picture).
Insert note about the 4.7K resistor recommended by Gottlieb here.

4.8 Display Problems

4.8.1 Open Slam Switch

File:Gtb 6digit slam.gif

Simulation of a Display Effected by an Open Slam Switch

If after turning a System 80 game on, and the displays turn on immediately without a 5 second delay, there is a problem. However, this is not a display issue, if the displays are showing all segments lit, and strobing rapidly. The problem is actually due to an open slam switch on the coin door.

4.12 Updating a dual game PROM MPU (1st generation) to a single game PROM configuration (2nd generation)

As noted earlier, the first five system 80 games used both sockets at PROM1 and PROM2, populating them with 8K byte masked ROMs. Should one of these ROMs fail, you may be able to find a replacement, but they are becoming more pricey, more difficult to find, and are still prone to failure as they age.

A more flexible solution would be to update the MPU to use a single 2716 UVEPROM at the PROM1 socket.

Modifications must be made to both the solder side and the component side of the board. See the pictures below.

Component side modification:

1. Cut the trace that extends from the left of Z10 between pins 6 and 7. A Dremel with a "ball shaped" cutter bit works beautifully for this. In the second picture below, the cut has already been made. I've filled the cut hole with black Sharpie! to better show the location of the cut.

Solder side modifications:

1. Cut the traces leading to PROM1 socket, pins 19 and 21. Again, the cuts have been highlighted with black Sharpie!
2. Jumper from the PROM1 socket, pin 19, to the PROM2 socket, pin 21 (connects A10)
3. Jumper from the PROM1 socket, pin 21, to the PROM2 socket, pin 24 (connects +5V to Vpp)
4. Jumper from the PROM1 socket, pin 22, to the PROM2 socket, pin 18 (connects A9)
5. Jumper from Z10, pin 13 to the via just below and to the right of Z9 (as you view the back of the board)

Your MPU board is now configured for any System 80 game. All that remains is to acquire a 2716 EPROM containing the game's code. If you have the original ROM images, the DOS command to combine them is shown below. Modify as appropriate to match the file names you have.

copy /b prom1.bin + prom2.bin combined.716

The MPU may also be used in a System 80A game if U2/U3 are updated, and in a System 80B game if considerably more mods are made which frankly, just aren't worth it.

• System 80 1st Generation to 2nd Generation Board Updates
• 

  Dremel Tool with "Ball Cutter"
• 

  Trace extending Left from Z10
• 

  PROM2-to-PROM1 Socket Cuts and Jumpers
• 

  Z10, pin 13 to via Jumper

4.13 Using a 2732 game PROM in a System 80B MPU

The Gottlieb documentation for using a 2732 game ROM at the PROM1 position is not correct (as shown in manuals for "Bad Girls" and "Big House", page 24). I've been unable to track down a service bulletin for this but clearly, for some games like Hot Shots, this is necessary. The following procedure makes AB10 (address bus 10) available at the game PROM.

Procedure:

1. If jumper E4 is installed, remove it. You will find E4 immediately to the right of the PROM1 socket.
2. Install a jumper at E3. This really just connects the pad marked E3 to the dual pad marked E4.
3. On the solder side of the board, follow the trace from the pad marked E3 Southwest and then South about 1/2 inch to a via.
4. Find this via on the component side of the board. It will extend to the left to another via.
5. Cut the trace between the two vias
6. On the solder side of the board, install a jumper from TC1, pin 6 to solder pad marked E3
7. E5 should remain installed, no change

5 Game Specific Problems and Fixes

5.1 Replacing the Black Hole "Spinning Disk" Motor

Here ya go Intrepid...have at it... :-)

Thanks, please be patient.....

6 Repair Logs

Did you do a repair? Log it here as a possible solution for others.

6.1 Game Displays 000000 On Power Up and It's Not The Slam Switch

If you power the game on and all of the displays immediately display all zeros without strobing the problem is usually with the slam switch. However, if the slam switch modification has been done or the slam switch is working properly there is a problem with the switch matrix.

I had this problem on my Haunted House machine. I finally found that chip Z15 (7432) was bad.

I was fixing a kicker solenoid on the playfield, the playfield was still in the machine and fully in the upright position. While I was soldering the wire to the new solenoid I did not adequately protect the components below from a solder drip. Well, I did have a solder drip that landed right on a pop bumper driver board connector and shorted the connector. The short caused more than just this problem but for this narrative we will restrict to the slam/switch matrix problem.

Reading in other materials I recognized the problem as the slam switch issue. I used a logic probe to test other components and found the CPU board working, mostly as it should except for acting like the machine was slam tilted. There was little written about the problem outside of the slam switch. I decided to check the matrix by doing a diode check on all of the diodes in the switch matrix. When I did this, I found that many of the diodes were testing bad. These were being tested with the board removed from the machine.

Having replacement diodes in my parts drawer I decided that these must have gone bad during the short. I began unsoldering a few of the diodes. Once disconnected from the circuit board I remeasured the removed diodes and found the correct values on my meter, they were not bad. I then noticed that the bad diodes were all in the same row on the switch matrix. They all traced back to the Z15 chip. I replaced the Z15 7432 and the problem was resolved.