Gottlieb System 80

From PinWiki
Jump to navigation Jump to search
ExclamationPoint.jpg
Note: This page is a work in progress. Please help get it to a completed state by adding any useful information to it.


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, 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 - Media:Gtb_sys80_sound.JPG
Panthera 06-1980 5220 652 Sound Only - Media:Gtb_sys80_sound.JPG
Circus 06-1980 1700 654 Sound Only- Media:Gtb_sys80_sound.JPG Ultra Widebody
Counterforce 06-1980 3870 656 Sound Only- Media:Gtb_sys80_sound.JPG
Star Race 08-1980 870 657 Sound Only- Media:Gtb_sys80_sound.JPG Ultra Widebody

2.2 System 80 2nd Generation

Title Date of Release Production# Model # Sound Notes
James Bond 10-1980 3625 658 Sound only - Media:Gtb_sys80_sound.JPG
Time Line 12-1980 3167 659 Sound Only - Media:Gtb_sys80_sound.JPG
Force II 12-1981 2000 661 Sound Only- Media:Gtb_sys80_sound.JPG
Pink Panther 03-1981 2840 664 Sound Only- Media:Gtb_sys80_sound.JPG
Mars God of War 03-1981 5240 666 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG First Gottlieb with speech, lane change, and multi-ball
Volcano 09-1981 3655 667 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG
Black Hole 10-1981 8774 668 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG First Gottlieb with 2-Level playing area, Export games used sound only board
Haunted House 06-1982 6835 669 Sound Only - Media:Gtb_sys80&a_s&s.JPG First game with 3-Level playing area, Sound only, but used sound & speech board
Eclipse 1982 193 671 Sound Only- Media:Gtb_sys80_sound.JPG 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 - Media:Gtb_sys80&a_s&s.JPG Export games may have used the sound only board - someone please confirm
Caveman 09-1982 1800 PV810 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG Pinball / Video game hybrid
Rocky 09-1982 1504 672 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG
Spirit 11-1982 1230 673 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG Sound only, but used sound & speech board
Punk! 12-1982 959 674 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG Sound only, but used sound & speech board
Striker 11-1982 910 675 Sound & Speech - Media:Gtb_sys80&a_s&s.JPG 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 - Media:Gtb_sys80&a_s&s.JPG
Super Orbit 05-1983 2100 680 Sound Only - Media:Gtb_sys80&a_s&s.JPG Sound only, but used sound & speech board
Royal Flush Deluxe 06-1983 2000 681 Sound Only- Media:Gtb_sys80&a_s&s.JPG Sound only, but used sound & speech board
Amazon Hunt 09-1983 1515 684 Sound Only- Media:Gtb_sys80&a_s&s.JPG Sound only, but used sound & speech board. Later production games used piggyback sound board
Rack 'Em Up! 11-1983 1762 685 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Ready... Aim... Fire! 11-1983 390 686 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Jacks to Open 05-1984 2350 687 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Alien Star 06-1984 1065 689 Sound Only - Media:Gtb_sys80a&b_sound.JPG 689A Denotes a revision in the ROM code
The Games 08-1984 1768 691 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Touchdown 10-1984 711 688 Sound Only - Media:Gtb_sys80a&b_sound.JPG
El Dorado City of Gold 09-1984 905 692 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Ice Fever 02-1985 1585 695 Sound Only - Media:Gtb_sys80a&b_sound.JPG

2.4 System 80b

Title Date of Release Production# Model # Sound Notes
Chicago Cubs Triple Play 05-1985 ~1365 696 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Bounty Hunter 07-1985 1220 694 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Tag Team Pinball 09-1985 1220 698 Sound Only - Media:Gtb_sys80a&b_sound.JPG
Rock 10-1985 1875 697 Sound Only - Media:GTB Sys80B Sound.JPG
Raven 03-1986 3550 702 Sound Only - Media:GTB Sys80B Sound.JPG
Rock Encore 04-1986 245 704 Sound Only - Media:GTB Sys80B Sound.JPG 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 - Media:GTB Sys80B Sound.JPG
Genesis 09-1986 3500 705 Sound Only - Media:GTB Sys80B Sound.JPG
Gold Wings 10-1986 3260 707 Sound Only - Media:GTB Sys80B Sound.JPG
Spring Break 04-1987 3550 706 Sound Only - Media:GTB Sys80B Sound.JPG
Monte Carlo 02-1987 4315 708 Sound Only - [[Media:GTB Sys80B Sound.JPG]
Arena 06-1987 3099 709 Sound Only - Media:GTB Sys80B Sound.JPG
Victory 10-1987 3315 710 Sound and speech - Media:Gtb sys80b MA886 sound.JPG
Diamond Lady 02-1988 2700 711 Unknown
TX Sector 03-1988 2336 712 Sound and speech - Media:Gtb sys80b MA886 sound.JPG
Robo-War 04-1988 2130 714 Unknown - - Media:Gtb sys80b MA886 sound.JPG
Excalibur 11-1988 1710 715 Unknown -- Media:Gtb sys80b MA886 sound.JPG
Bad Girls 11-1988 2500 717 Sound and speech - Media:Gtb sys80b MA886 sound.JPG
Big House 04-1989 1977 713 Sound and speech - Media:Gtb sys80b MA886 sound.JPG
Hot Shots 04-1989 2342 718 Sound and speech - Media:Gtb sys80b MA886 sound.JPG
Bone Busters Inc. 08-1989 2000 719 Sound and Speech - Media:Gtb sys80b MA886 sound.JPG 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

Gottlieb System 80 Board Diagram

3.2 System 80 / 80A / 80B Satellite Boards

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 A1-J2 and A1-J3 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 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


Sys80 switch matrix.png

3.4.1 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.


3.4.2 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.

3.5 Power Supply

3.6 CPU Board

Gottlieb System 80 CPU Board


3.7 Driver Board

The System 80 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.

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.

The games' sound signals (S1, S2, S4, S8) also pass through the driver board at Z14, 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.

3.8 Sound Boards

3.9 Sound Board Power Supplies

3.10 Displays

3.10.1 System 80 - 6 Digit Displays

Gottlieb System 80 Display Diagram


3.10.2 System 80A - 7 Digit Displays

Gottlieb System 80A Display Diagram


3.11 Bookkeeping & Diagnostics

Gottlieb System 80 Coin Door Test Button Highlighted



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 now show "00", then press the start switch and the CPU will enter its diagnostic mode (or press the self test switch again for bookkeeping.) Pressing the self test switch will advance it to the next test.

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 slams
10 Times HGTD has been beaten
11 First high score level
12 Second high score level
13 Third high score level
14 High game to date score
15 Average playing time

Diagnostics
16 Lamp output test
17 Coil output test (will cycle and display #)
18 Switch test. (99 = no fault) You can also check switch numbers by pressing them on the playfield now.
19 Display test. Displays will cycle through numbers
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

4.1 Ground updates

4.2 Power Problems

Bridges, orange cap in cabinet

4.3 MPU boot issues

4.3.1 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.

4.3.2 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.

4.3.3 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.

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.


4.3.4 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.

4.3.5 Using a PC Power Supply For Bench Testing

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! --Kencaine 02:30, 24 April 2011 (BST)


4.4 Game resets

4.5 Solenoid problems

4.6 Lamp problems

4.7 Switch problems

4.8 Display problems

4.9 Sound problems

4.10 Flipper problems

4.11 Pop bumper problems

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.

Component side modifications:

Solder side modifications:

Your MPU board is now configured for any System 80 (but not 80A or 80B) game. All that remains is to acquire a 2716 EPROM containing the game's code.

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

Need a jumper from TC1 pin x to J3, IIRC...need to verify...Chris Hibler

5 Game Specific Problems and Fixes

Example would be servo controller on Independence Day pinball

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. --Kencaine 01:43, 24 April 2011 (BST)