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Scope.
This document is a repair guide for Bally electronic pinball games made from 1977 to 1985. Since Stern electronic pinball games use nearly identical electronics, these games are covered too.

Internet Availability of this Document.
Updates of this document are available for no cost at http://marvin3m.com/fix.htm if you have Internet access. This document is part three of three (part one is here, and part two is here).

IMPORTANT: Before Starting!
IF YOU HAVE NO EXPERIENCE IN CIRCUIT BOARD REPAIR, YOU SHOULD NOT TRY TO FIX YOUR OWN PINBALL GAME! Before you start any pinball circuit board repair, review the document at http://marvin3m.com/begin, which goes over the basics of circuit board repair. Since these pinball repair documents have been available, repair facilities are reporting a dramatic increase in the number of ruined ("hacked") circuit boards sent in for repair. Most repair facilities will NOT repair your circuit board after it has been unsuccessfully repaired ("hacked").

If you aren't up to repairing pinball circuit boards yourself or need pinball parts or just want to buy a restored game, I recommend seeing the suggested parts & repair sources web page.

Table of Contents

1. Getting Started:
1. Experience, Schematics, Manuals
2. Necessary Tools
3. Parts to have On-Hand
4. Game List
5. Lubrication Notes
6. The Circuit Boards
7. Voltage Test Points on the Boards
8. Fuse Values/Usage & Power Supply Power Distribution

2. Before Turning the Game On:

1. Check the Coil Resistance
2. Removing the MPU Battery and Fixing Corrosion
3. Rebuilding the Power Supply
4. Upgrading the Voltage Regulator/Solenoid Driver Board
5. Upgrading the Ground on the MPU Board
6. Pre Power-On Voltage Checks
7. Connectors
8. Setting Free Play

3. When Things Don't Work:

1. Making a MPU test fixture
2. Fixing the MPU (LED flashes and the such)
3. Test EPROM & Fixing a Dead MPU board
4. Game ROMs, EPROMs, and Jumper - the Basics
5. -35 MPU Game ROMs, EPROMs, and Jumpers
6. -17 MPU Game ROMs, EPROMs, and Jumpers
7. Stern M-200 MPU Jumpers (using a Stern M-200 in a Bally Game)
8. Converting a -133 MPU (Baby Pacman) to a -35 MPU
9. The Built-In Diagnostics/Bookkeeping
10. Coils: Locked-on, Sporadic, or Not Working (Solenoid Driver board) including Flipper Coils
11. Lamps: Locked-on or Not Working Feature Lamps (Lamp Driver board)
12. Solenoid Expander Board Problems
13. Auxiliary Lamp Driver Board Problems
14. Switches and the Switch Matrix
15. High Voltage Section Problems (No Score Display Power)
16. Score Display Fixes and Replacements
17. Reset or Lockup Power Problems
18. Sound Board Problems
19. Flipper Maintenance
20. Miscellaneous Problems and Fixes

Important: Before you Change any Jumpers!!
It is EXTREMELY important that you have a working MPU board before you change any jumper locations! If the MPU board currently has ROMs in it, get it working first before playing with the jumpers. If the MPU board is jumpered incorrectly for the game ROMs installed, the diagnostic LED light will stay on, and the board will not power-up. So it is absolutely important that the jumpers are correct for the ROMs installed. Get the MPU board working first before proceeding.

Also of course, make sure the board being worked on is a AS-2518-35 (or AS-2518-133) MPU (remember the -133 is really a -35 board with R113 changed to a diode CR52). The easiest way to tell (besides looking at the silkscreened part number on the board!) is to examine connector J5. On a -35/-133 MPU board, J5 will have 33 pins (including the removed "key" pin).

Max out ROM Memory on the -35/-133 MPU to use 2732 EPROMs.
Jumpering is not a big problem until the MPU's ROM chips begin to fail, and MPU boards are shifted from game to game. An MPU board can only be jumpered so many times before the traces and jumpers start to lift and strip off the board. So instead of custom jumpering a board to a particular set of ROMs, the best idea is to maximize the board to use the largest EPROM size, and cater the EPROMs themselves to the board (instead of the other way around).

This really makes sense as the largest EPROMs that will fit the -35/-133 MPU board are 2732's, which are commonly and cheaply available. For this reason, the Bally ROM code has been re-formated to fit this size EPROM. The original program size and code is still available from Williams at www.pinball.com/Williams/tech/roms.html. But I highly suggest you down load the ZIP file bly2732.zip instead, as it contains all the Bally ROMs for all games from Freedom (1977) to Cybernaut (1985), and has been converted to 2732 format. Only Baby Pacman and Granny and the Gators ROMs are missing from this file. Using these files will allow you to use a -35 MPU board for ANY Bally game from 1977 to 1985. Click here for a list of the ROM files, and which games use which ROMs (note many games share the same U6 ROM). Text file from Mr. Calahan.

For the -35/-133 MPU board, using all 2732 for ANY game has the advantage of just one set of jumpers. Just download the above file and expand it, and burn your game into 2732 EPROMs. Then jumper your -35 MPU board like this:
1. Jump E4 to E13a
2. Jump E12 to GND (large GND trace next to the ROM sockets, left of E12)
3. Jump E7 to E8
4. Jump E10 to E11
5. Jump E31 to E32
6. Jump E16a to E29 (on -133 "E16 to E29")
7. Jump E33 to E35
Note: any jumpers still installed (from the old ROM setup) that are not listed above should be removed.

Jumpers around the U1 socket, for using two 2732 EPROMs: Jumpers E4 to E13a (top white wire), E12 to GND (right white wire), E7 to E8 (middle left), and E10 to E11 (lower right).

Jumpers around the U6 socket, for using two 2732 EPROMs: E31 to E32, E16a to E29, and E33 to E35.

If you don't want to convert your game to 2732 format, you can also use these jumpers for other types of ROMs in your -35/-133 MPU board.

Using 2532 EPROMs instead of 9332 Masked ROMs.
If the game in question is a later Bally game with 9332 masked ROMs, these can be changed to 2532 EPROMs with NO jumper modifications! This can be handy and convenient if the original black 9332 masked ROMs need changing, but the repair person doesn't want to mess with the jumpers.

The "Mother" Source for Jumper Info.
All the following jumper information came from several sources. The primary source is, of course, the original MPU board schematics. There were also two secondary sources too. First was Williams web site, located at bally_read1st.txt which contains all the jumper info you will probably need. Also Joel Cook's "Pinball Lizard" Tech Tips Guide #1 has this information too. I highly suggest the Joel Cook "lizard" tech books; they have lots of other good pinball repair information too. You can buy these from Marco Specialties at http://www.pinballmachine.com.

Stuff to remember:
• Bally uses a preceding "E" on all jumper numbers. Yes, the "E" has been left out above to save some space in the chart.
• The "dash" between the numbers is the "jump". That is, "1-4" means a jumper from E1 to E4.
• Remove any jumpers not shown above for a given configuration. If it's not mentioned above for your ROM set up, you don't need that jumper!
• Don't trust other Bally jumper charts! The above chart is "the one to use" (using Bally published jumper charts can lead to problems).
• You must know the ROM device type installed at each ROM location. The Bally part number (often printed on the ROM) does not help.
• BLACK masked ROMs, as used in many Bally games, are entirely black and usually have some white part numbers printed on them. These are known as 9316 masked ROMs.
• EPROMs, on the other hand, have a small clear "window" on their top, often with a sticker over the window. The sticker is there for a reason; it prevents UV light from entering the EPROM's clear window (this is how an EPROM is erased! so keep the sticker on the window). EPROMs are labeled as to their size (i.e. "2716").
• The most common EPROMs used on Bally MPU boards are 2716, 2532 and 2732 EPROMs.
• ROMs and EPROMs are game specific. Each game has its own custom set of ROM computer code, stored on that game's ROMs (or EPROMs).
• Some EPROM part numbers are interchangable. For example, 2532 EPROMs, 9332 masked ROMs, and 8332 masked ROMs all use the same jumper setting. But a U2 2532 EPROM from a Kiss game is NOT interchangable with a U2 9332 EPROM from a Strikes and Spares! This also applies to the 16 bit masked ROMs too. That is, 9316 masked ROMs, 8316 masked ROMs, and 8516 masked ROMs all use the same jumper settings. But again a U2 9316 ROM from a Kiss game is NOT interchangable with a U2 8316 ROM from a Strikes and Spares!

Freedom and Night Rider ROMs and Jumper Notes if using U1,U6.
These two games used a strange 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. The old Williams tech web site at www.pinball.com states that a U1 2716 EPROM and a U6 2716 EPROM can be used for these two games (and provides the ROM files for download, and the jumper settings for the -35 MPU board).

Note I have also tested both games with 2732 EPROMs at U2 and U6 on a converted -17 and -35 MPU boards (as documented above). This does in fact work fine for both Freedom and Night Rider, and is a better solution in my opinion.

E13, E15 Mistaken Jumper Locations.
There are two jumper pads near the lower right hand corner of the U2 ROM socket labeled "E13" and "E15". There are also two vias (plated through holes) just a little bit further to the right, which are actually closer to the "E13" and "E15" labels. The vias are completely unrelated to the labeled jumper pads. Be careful when using these jumpers that you don't confuse the vias with the jumper pads. They are both round plated through holes, but the jumper pads are a bit bigger.

Important: Before you Change any Jumpers!!
It is EXTREMELY important that you have a working MPU board before you change any jumper locations! If the MPU board currently has ROMs in it, get it working first before playing with the jumpers. If the MPU board is jumpered incorrectly for the game ROMs installed, the diagnostic LED light will stay on, and the board will not power-up. So it is absolutely important that the jumpers are correct for the ROMs installed. Get the MPU board working first before proceeding. If the ROMs are suspect as bad, and the MPU board is set up for 9316 ROMs (most -17 boards are), see the section below, "Making an Adapter to use Two 2716 EPROMs in an Unmodified -17 MPU board that is Jumpered for 9316 ROMs". This will allow the use of two new 2716 EPROMs to replace the failed 9316 ROMs, without any MPU board modifications or new jumper settings.

Also of course, make sure the board being worked on is a AS-2518-17 MPU. The easiest way to tell (besides looking at the silkscreened part number on the board!) is to examine connector J5. On a -17 MPU MPU board, this connector will have 32 pins (including the removed "key" pin).

Bad MPU Board Sockets ("closed frame" sockets).
If a Bally MPU board is using brown or black closed frame sockets (closed frame means the circuit board under the socket can not be seen), or sockets that have "SCANBE" or "RS" impressed on them, it is advised they be changed! These older sockets are very troublesome and cause many intermittent problems. A quick alternative to replacement is to plug a machine pin socket into the brown socket. This is a *temporary* fix, but should work well enough until the board is working, and then later replace the sockets).

A brown and a black closed frame socket. There's no way around it, ALL these sockets will need to be replaced on any Bally MPU board.

Jumpers used on the Early -17 MPU (and Stern M-100).
The 1977 to 1979 Bally -17 MPU boards aren't as versatile as the newer -35 boards. They have limited ROM space, which means they can't be used in the newer 1979 to 1985 games. This can all be rectified, but will require some cutting and jumping of traces on the -17 MPU board.

There are only a few jumper choices on the -17 MPU board. The following jumpers only apply for the early 1977 to 1979 Bally -17 MPU board. Note the configuration that uses a U1 ROM only existed for the first two Bally games, Freedom and Night Rider.

Stuff to remember:

• Bally uses a preceding "E" on all jumper numbers. Yes, the "E" has been left out above to save some space in the chart.
• The "dash" between the numbers is the "jump". That is, "1-4" means a jumper from E1 to E4.
• Remove any jumpers not shown above for a given configuration. If it's not mentioned above for your ROM set up, you don't need that jumper!
• You must know the ROM device type installed at each ROM location. The Bally part number (often printed on the ROM) does not help.
• BLACK masked ROMs, as used in many Bally games, are entirely black and usually have some white part numbers printed on them. These are known as 9316 masked ROMs (though Freedom and Night Rider can also use 74S474 or 7461 masked ROMs).
• EPROMs, on the other hand, have a small clear "window" on their top, often with a sticker over the window. The sticker is there for a reason; it prevents UV light from entering the EPROM's clear window (this is how an EPROM is erased! so keep the sticker on the window). EPROMs are labeled as to their size (i.e. "2716").
• ROMs and EPROMs are game specific. Each game has its own custom set of ROM computer code, stored on that game's ROMs (or EPROMs).
• Some EPROM part numbers are interchangable. For example, 2532=9332=8332. But a U2 2532 EPROM from a Kiss game is NOT interchangable with a U2 9332 EPROM from a Strikes and Spares!

Mod1: 2716 at U2,U6 on a Bally -17 or Stern M-100.
**Freedom/Night Rider with 2716 at U2/U6.
The most common conversion on a -17 or M100 CPU board (other than converting a -17 board to use 2732 EPROMs). In addition to the jumpers listed above (1-2, 3-4, 6-7, 8-10), must also make the following cuts and jumps to use 2716 EPROMs at U2/U6.

1. Make sure jumpers E1-E2, E3-E4, E6-E7, and E8-E10 are in place.
2. On the solder side of the board, cut the trace leading to U18 pin 4.
3. On the solder side of the board, run a jumper from the via above U3 pin 6 (that had its trace cut in the prior step) to U18 pin 5. This connects U18 pin 5 to U2 pin 18.
4. On the solder side of the board, cut the trace leading to U2 pin 21.
5. On the solder side of the board, cut the trace leading to U6 pin 21.
6. On the solder side of the board, run a jumper from U2 pin 21 to U2 pin 24.
7. On the solder side of the board, run a jumper from U6 pin 21 to U6 pin 24.
8. For Freedom and Night Rider, be sure to put the 2716 U1 chip in the U2 socket.

Mod1/2: When using 2716s at U2 & U6, or a single 2732 at U2, make these modifications at chip U18: cut the trace going to U18 pin 4, and connect U18 pin 5 to the cut trace's via (which is above U3 pin 6).

Mod2: The -17/M100 component side modifications for a single 2732 at U2. Make the trace cut shown next to U2's large ground trace, and then connect E4 to the via above the cut trace, and then E3 to the large ground trace.

Mod3: 2716 at U2, 9316 at U6 on a Bally -17 or Stern M-100 MPU board.
In addition to the jumpers listed above (1-2, 3-4, 6-7, 8-10), must also make the following cuts and jumps to use this configuration.
1. On the componet side, cut the trace from U2 pin 18 to U3 pin 18. Best place to do this is where the trace passes between sockets U2 and U3. Use your DMM set to continuity to help figure out the trace to cut.
2. On the solder side, run a jumper from U2 pin 18 to U17 pin 11.
3. On the solder side, cut the trace going to U2 pin 21.
4. On the solder side, run a jumper from U2 pin 21 to U2 pin 24.

Mod4: 2732 EPROMs at U2,U6 on a Bally -17 or Stern M-100 board.
AKA Converting a Bally -17 or Stern M-100 to a Bally -35 MPU.
This modification allows a Bally -17 or Stern M-100 MPU board to be used on any Bally game up to 1985. It doubles the amount of ROM space the older MPU board can use, and essentially makes a Bally -17 or Stern M-100 MPU board a Bally -35 MPU board. Note you can not use a -35 Bally board in a Stern games requiring a M-200 MPU (these boards have two 5101 RAMs instead of one as used on a Bally -35 MPU).

In addition to the jumpers listed above (1-2, 3-5, 6-7, 8-10), you must also make the following cuts and jumps to use this configuration.

1. Make sure jumpers E1-E2, E3-E5, E6-E7, and E8-E10 are in place.
2. Double check jumper E3 connects to E5.
3. On the solder side, cut the trace that runs to U2 pin 21.
4. On the component side, 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 your DMM set to continuity to help figure out the trace to cut.
5. On the solder side, jump a wire from U2 pin 18 to U2 pin 12.
6. On the soider side, jump a wire from U2 pin 21 to U9 (CPU) pin 24.
7. On the solder side, cut the trace that runs to U6 pin 21.
8. On the component side, cut the trace that runs to U6 pin 18. Best place to do this is where the trace passes between sockets U6 and U5. Use your DMM set to continuity to help figure out the trace to cut.
9. On the solder side, jump a wire from U6 pin 18 to U6 pin 12.
10. 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).
11. On the solder side, cut the trace that runs to U17 pin 2.
12. On the solder side, cut the trace that runs to U18 pin 4.
13. On the solder side, jump a wire U17 pin 2 to U18 pin 4.

Making an Adapter to use Two 2716 EPROMs in an Unmodified -17 MPU board that is Jumpered for 9316 ROMs.
This is a great adapter to have around when working on a -17 board that you don't want to modify. It will allow you to use a pair of 2716 EPROMs on a stock, unmodified -17 MPU board. This allows testing of the board without making any cuts or jumps.

Basically it takes four good quality (machine pin) 24 pin sockets, and sandwiches two of them together. There are a couple pins that need to be cut, and a couple jumper wires added (see the diagram below):

• On two of the 24 pin sockets, jump pins 21 and 24 together with some wire.
• On the two sockets you modified above, solder a four inch wire to pin 18. Then solder the sockets' pin 18 wires together, and attach a test clip to this wire too.
• On the two sockets you modified above, cut pins 18 and 21 short so they won't plug into anything.
• Plug the two modified sockets into the other two unmodified sockets. Make sure pins 18 and 21 do not contact the unmodified sockets. To be double sure this happens, you can cut pins 18 and 21 off the bottom sockets too.
• Plug the 2716 EPROMs for U2 and U6 into the two modified sockets.
• Plug the sandwiched sockets and EPROMs into the MPU board at positions U2 and U6.
• Connect the test lead coming off pin 18 of the two modified sockets to the right side of R14 (the side nearest the ROM sockets).

Freedom and Night Rider ROMs and Jumper Notes if using U1,U6.
These two games used a strange 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. The old Williams tech web site at www.pinball.com states that a U1 2716 EPROM and a U6 2716 EPROM can be used for these two games (and provides the ROM files for download, and the jumper settings for the -35 MPU board).

If using a -17 MPU with a U1 2716 EPROM and U6 2716 EPROM, there are some other cuts and jumps required:

• Cut the trace from U1 pin 18 to U2 pin 18.
• Cut the trace from U1 pin 21 to jumper pad E7.
• Connect U1 pin 21 to U1 pin 24.
• Connect U1 pin 18 to U17 pin 11.
• Connect U1 pin 22 to U2 pin 22.

Note I have tested both games with 2732 EPROMs at U2 and U6 on a converted -17 MPU board (as documented above). This does in fact work fine for both Freedom and Night Rider.

Bally's chart for ROMs in a -17 MPU board (U1,U2,U6 are all 9316 ROMs).

Some Unique MPU-200 Facts.
There some unique relatively unknown features of the Stern MPU-200:
• On an MPU-200, if all 32 dip switches are turned off (open), at power-on 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.
• 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 upper 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 13-14 to 13-15, and 5-7 to 1-5.

Stern M-200 and the 5101 RAM chips (boot up problems).
The Stern M-200 MPU board uses two 5101 RAM chips (instead of just one like Bally and Stern M-100 MPU boards). When buying 5101 chips, the standard speed rating on this chips is 300 ns. This works fine for Bally and M-100 MPU's, but the Stern M-200 (which runs at a higher clock speed) requires a faster 5101 RAM chip, at 100 ns. The faster 100 ns chip is labeled as 5101-1, and the slower 300 ns chip is labeled as 5101-3. If you use the slower 5101-3 RAM chip in a Stern M-200 MPU board, the board may not boot up correctly; you can get the seventh LED flash, but the game just doesn't work right. Often this can be indicated by the game audits and high scores, where a number (like '74') is continually repeated in all the audits or high scores. Remember, if using a M-200 MPU in a Bally game, the second 5101 RAM at U13 can be removed (the Bally ROM software does not use this chip).

In 1982 Bally changed their -35 MPU board very slightly to work in the combination pinball/video games Baby Pacman and Granny and the Gators, and also was used in Grand Slam. If you want to use this MPU in other pinball games, you need to convert it to a -35 MPU.

Zero Crossing Change.
The "Zero Crossing Circuit" is used to protect circuits from damage. It has to do with AC voltage, which alternates from negative voltage to positive voltage 60 times a second (or 50 times a second in Europe). This means 120 times per second AC voltage is momentarily zero, as it passes through the zero crossing point in the AC wave form. It's 120 times per second because the voltage goes from plus to minus and back through zero to plus again twice every cycle. By turning on lamps and solenoids as the power line passes through the zero point, large current surges are avoided, extending their lives. In Bally and Stern games, the CPU monitors the Zero Crossing circuit to know when to switch on CPU controlled lamps and solenoids.

Bally pins from 1977 to 1983 use the 43 volt solenoid voltage to monitor the zero crossing. Now I know what you are thinking, that the 43 solenoid voltage is DC not AC. But it is full wave rectified with no filter capacitor, so the circuit can see the voltage change from about 38 volts DC to 47 volts DC, and use 43 volts DC as the zero crossing point. But starting with Granny and the Gator, Baby Pacman, and Grand Slam, they changed the MPU board slightly to use the 6 volt AC for the General Illumination lights for the zero cross circuit. This was done by changing the 2K ohm resistor at R113 to a 1N4148 diode.

The reason Bally changed the circuit to use AC instead of DC was to be able to double the number of CPU controlled lamps used in a game without adding circuitry. With the half rectified pulsing DC, one could not tell which half cycle was on. By switching to the AC, the MPU board could know if the AC was going positive or going negative. With this, the MPU could turn on the SCRs that drove a particular set of lamps, depending on the phase (negative or positive). To do this each SCR supplies two lamps in series, and the lamps have diodes across them. The diodes are placed such that one diode will be forward conducting to shunt the current around that lamp while the other diode is blocking to light the lamp that is in parallel with that diode (hence the two lamps each have a diode installed in reverse direction to each other). This way one SCR can distinctly control two different lamps in different manner, essentially doubling the number of CPU controlled lamps in the game. Thanks to Dwight for this explaination.

How Do I know If My Game Needs a -133 MPU?
If a -35 or -17 CPU board (with a resistor installed at R113) is put in a game requiring a -133 CPU board, it just won't boot until the resistor is changed to a 1N4148 diode. But if a -133 CPU board (with a diode installed at R113) is installed in an earlier game requiring a -17 or -35 CPU board, damage will be caused to the CPU board. That's because there is no longer a 2k ohm resistor to buffer the 43 volts, and it sends 43 volts across components expecting a much lower voltage, and this of course damages them.

To determine if a game needs a -133 MPU board, measure the voltage at the MPU board's J4 pin 15 (connector removed). If it measures 6.3 volts AC (instead of 43 volts DC), then this particular game should be using a -133 MPU board (Granny and the Gator, Baby Pacman, Grand Slam). Note with a -133 MPU board installed, MPU board TP3 should show about 5 volts DC (instead of 21 volts DC as on a -35 MPU board).

Converting a -133 MPU to a -35 MPU.
Converting the -133 MPU to a -35 MPU is very easy do. Just replace the 1N4148 diode at CR52 (R113) with a 2k 1/4 watt resistor. This was the only change made. This diode is on the lower left corner of the MPU board, next to connect J4. On an original -35 MPU, this resistor is labeled R113, not CR52. Likewise converting a -35 MPU board to a -133 just involves changed R113 from a resistor to a 1N4148 diode. The striped end of the diode (cathode) should connect to capacitor C1 (that is the diode's band should be furthest away from J4).

Left: a Baby Pacman -133 board that was converted to a -35 board. Note the 2k resistor installed in place of "CR52".	Right: a -35 MPU board. Note the 2k resistor is labeled "R113".

You may also need to re-jump the board for the ROMs you will be using (typically Baby Pacman came with a 2732 U2 EPROM, and a 2532 U6 EPROM).

Converting a -35 MPU to a -133 MPU for use in Baby Pacman.
If you have a pinball -35 MPU that you want to put into a Baby Pacman game, this of course is easy too. Just remove the 2k resistor R113 and replace it with a 1N4148 or 1N914 diode. The non-banded side of the diode connectors to the J4 header pin 15 (diode band goes towards capacitor C1).

If you game "boots" correctly and goes into attract mode, you can use the built-in diagnostics for the game. This is done by pressing the red test switch mounted inside the coin door. If this switch does not work, alternatively you can short the MPU board connector J3 pin 1 to ground. If self test still does not begin, there is a problem with the MPU board. If diagnostics do begin, the problem is in the wiring or J3 connector, or in the coin door connector.

Here's what happens each time the test button is pressed:

The red self-test diagnostic button inside the coin door.

1. Lamp Test (CPU controlled Lamps). The first test is for all switched feature lamps; they will flash off and on continuously. You can check for burnt bulbs, lights that are never on, or lights that are always on (lamp driver board problems).
2. Score Displays. The second test is for the score displays. Each digit on each score display will cycle from 0 to 9, and repeat continuously. Broken diplays will have digits or segments always on or always off.
3. Solenoid Test. The third test is the solenoid test. Each solenoid will be energized, one at a time, in a continous sequence. Holding both flipper buttons "in" during this test will display the solenoid number being tested on the score display. Correct operation is indicated by the sound of a coil pulling in as its number appears on the display. If a coil makes no sound, note the coil number on the display and check out that coil. The game manual will tell you which coil the solenoid number correspond to.
4. Sound Test. The fourth button push is the sound card test (only on games equipped with one, Lost World and later; "chime" games do not have this test). A tune will be played repeatedly. Improper operation (no sound or distorted sound) can easily be heard.
5. Switch Matrix Test. The last test is the switch test. The MPU will search each switch for stuck contacts. If any are found, the switch number of the first stuck switch is flashed on the score display. Additional switches will be flashed until the last stuck switch is found. The last switch number will remain until the fault is cleared. Then the previous stuck switch is displayed. If no stuck switches are found, the number zero appears in the Match/Ball in Play display.
6. Bookkeeping. After the diagnostic test, the game will go into bookkeeping and adjustments mode. Each press of the red button will display a bookkeeping ID number, and the its value. Refer to your game manual for a description of each ID number. Note some 1982 and later Bally games also have some game adjustments available in addition to the bookkeeping. Again, see your game manual.
To exit the test mode, turn the game off and then back on.

How Coils are Energized (a Technical Introduction).
The basis behind pinball coils is that there is coil voltage at all coils at all times. Coil power is "daisy chained" from one coil to another under the playfield. Each coil is energized by completing its path to ground momentarily using two transistors on the solenoid driver board (a large SE9302/TIP102 style transistor, and a smaller pre-driver transistor contained in a CA3081 chip), allowing the coil to fire. That's why a DMM can be used to check for 43 volts on either coil lug when the game is on and in attract mode (not being played). If coil voltage is missing, either a fuse is blown or the power wire "up stream" has broken.

The following introduction text is thanks to Steve Kulpa and his web page at geocities.com/stevekulpa/bally_sole.htm. He did a really nice job of describing how the system works, so his text is transplanted here with some modifications. This information applies to the AS2518-22 and AS2518-17 solenoid driver boards, used in most Bally 1977 to 1985 games.

The solenoid driver board actually has two functions: The first obviously is to drive the solenoid and relay coils of the pinball, and the second is a voltage regulator. This provides regulated voltages to the other boards, plus high voltage (190v) to the score display driver boards. The voltage regulator stuff won't be discussed here, just the solenoid driver parts. Since the Solenoid Driver board contains the high voltage circuitry for the score displays, there is 190 volts DC on the board. Be careful as this is high voltage, and a shock from 190 volts DC will hurt.

We'll be discussing things from two circuit boards: The MPU board (AS2517-35 or AS2517-17) and the Solenoid Driver board (AS2518-22 or AS2518-17). The solenoid driver gets signals from the MPU board. These signals tell the solenoid driver which solenoid to fire. Up to 15 solenoids plus the flippers (via the flipper relay) can be controlled by the solenoid driver board.

Four signals from the MPU's U11 PIA chip travel out from the MPU board connector J4 pins 5-8,10 to the Solenoid Driver board connector J4 pins 3-7. These four signals tell the Solenoid Driver board which solenoid to fire. This is accomplished by using a 74154 decoder chip that takes the binary pattern of the four signals (16 different patterns) and decodes (or demultiplexes) them into one of sixteen different outputs. The four signals are applied to the decoder then the decoder is strobed. Normally, all sixteen of the decoder output lines are held high (+5 vdc). When strobed, the decoder lowers one of it's sixteen output lines, depending on the pattern of the four input signals.

With no input supplied (strobe is high), the output lines of the 74154 decoder are high (+5 vdc). This puts a voltage at the base of Q1 (this transistor is one of 7 in the CA3081 chip). This turns Q1 "on" and the voltage supplied to it's collector via resistor R1 passes through the transistor to ground. At this point, little or no voltage is present at the base of the large SE9302/TIP102 driver transistor Q2, and hence it is "off". With the SE9302/TIP102 driver transistor off, the 43 vdc at the coil has no place to go, and the coil remains de-energized.

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 the CA3081's predriver Q1 "off" (notice one of the two strobe lines goes to ground, so it's always low). This allows the +5 vdc at the Q1 CA3081'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 the TIP102 (Q2) turns on, the 43 vdc at the solenoid now has a path to ground through Q1 and current flows through the coil, thereby energizing it. Then the strobe to the decoder is released, the decoder output goes high again, and everything is back to normal.

A diode, resistor, and capacitor work to slow the speed at which the TIP102 and the solenoid are able to turn off. This is important to prevent the "inductive kick" voltage that builds up when a solenoid is turned off quickly. A solenoid coil can build up hundreds of volts if it is switched off quickly. For example, the spark in the sparkplug of a car is generated from this inductive kick when the ignition coil is turned off quickly. In this case, the diode allows the TIP102 and the solenoid to turn ON quickly (which is OK), because the current that used to be flowing through the CA3081's pre-driver transistor can now flow forward through the diode and turn on the TIP102 on quickly. However, when the decoder output goes back to high and the CA3081's pre-driver transistor turns back on, the diode prevents the charge from the base of the TIP102 driver transistor from being sucked down the CA3081's pre-driver transistor. The charge on the capacitor must drain off (slowly) through the resistor and the base of the TIP102. This takes awhile and slows the turn-off of the TIP102 and the solenoid coil, thus reducing the kick. Also, as the solenoid turns off and the voltage on the collector of the TIP102 starts to rise, this voltage is "fed back" by the capacitor to the base of the TIP102 and tends to keep it on a little longer, slowing the turn-off of the solenoid even more. Another diode across the solenoid works to absorb the solenoid's turn-off kick by conducting when the voltage on the collector of the TIP102 is greater than about 43 volts.

SDB Component Guide Document.
J.McAfee made this nice document of the SDB. Check it out here.

Coin Door Lockout Coil.
The Bally coin door has a coil known as the coin lockout coil. It is a small relay-shaped coil that often energizes when the game is powered on. It triggers a mechanism that allows the game to accept coins. For example if the machine is powered off and a patron puts money in the game, the money is rejected and returned at the coin return slot. But if game is powered on and the coin lockout coil is energized, the game will accept the money and add credits to the game.

Early Bally SS games momentarily turn off the coin lockout coil during game play when the ball enters the outhole, and turns it on again just before serving the next ball or going to Game-Over. Sometimes you can hear this clicking noise at the coin door during game play, and often people will be annoyed by this or think the game has a problem.

The coin lockout coil has no use unless you want the game to accept coins. For this reason many people clip one of the wires (the thinner wire going to the non-banded diode coil lug) to the coil because they don't like the clicking sound or buzzing noise. If your Bally game sometimes clicks at the coin door and is being used at home, you can disconnect this coin lockout coil without any problems.

Also since the coin door lockout coil is on all the time, as a rule, I personally always cut the thinner ground wire (going to the non-banded diode coil lug) to disconnect the coil. Why you ask? Because sometimes this coil can burn (from being on all the time), and cause the solenoid fuse to blow. After checking every other coil in the game and then realizing the problem is the coin door lockout coil, it can get pretty frustrating. Because of this I always disable this coil and set my game to a low replay or have an exterior coin button or a free play option.

Sporadic Coil Firing (and Random Tilts).
Say the game in question has a pop bumper or a slingshot that just fires by itself, on and then off. The coil's switch is good, and is not gapped too closely, and is not closed. But the coil is just going on and off sporadically for no reason. What could this be?

Because Bally felt many high-action coils (slingshots, pop bumpers, etc.) may have quick switch closures, and the relatively slow CPU may not see the switch closure, a capacitor was added to the coil switch. This small green or brown DISC capacitor lengthened the switch closure, helping the CPU to see when that switch was closed. Unfortunately these switch caps often fail, causing "phantom" switch closures. This makes the coil in question fire for no apparent reason during the game.

Switch capacitor failure probably happened because of the high power industrial soldering irons used on the assembly line. The caps used for the switches were actually made for circuit boards. As a result the high powered soldering irons on the assembly line weakened the cap's internal insulation, causing it to leak (not function reliably) with time.

To verify this is the problem, just cut one leg of the disc capacitor off the switch. Be careful when cutting this capacitor; don't cut the small tubular diode from the switch too! (The diode is absolutely needed.) The original switch capacitors were .05 mfd or .047 mfd, 16 volt (or greater), ceramic disc, non-polarized (today the easiest to find replacement is usually .047 mfd 50 volt non-polarized caps). After cutting one leg of the capacitor, see if that fixes the problem. If it is the problem, replace the capacitor next time you're at Radio Shack or ordering electronic parts. The cap helps the game detect quick switch closures, and effectively makes the pop bumpers play better (more sensitive). But it's not absolutely necessary to have the capacitor (it can be cut off completely and not replaced). In most cases the CPU is fast enough to see all switch closures. But the best thing to do is to replace the capacitor.

Another place this switch capacitor is often see is on the plumb-bob tilt. A failed switch capacitor here will make the game tilt for no apparent reason during game play. Definately cut this capacitor off, and don't replace it!

No Coils Working Diagnostics.
If none of the coils work, first look at the power supply:

• Rectifier board test point 5 (TP5, top right test point) should be 43 volts DC. If no 43 volts here, check fuse F4. Remove the fuse and check it with a DMM set to ohms ("buzz out" the fuse).
• The reason we remove fuses is to force a verification that the fuse holder is in good condition. The fuse holder clips can fatigue or burn, and often need to be replaced. If this is the case, 43 volts may not be getting to the rest of the game.
• If fuse F4 is good, the lack of 43 volts at TP5 is probably due to a failed (open) bridge rectifier BR3 on the rectifier board.
• If fuse F4 is bad, and a new fuse immediately blows at power-up, then bridge rectifier BR3 on the rectifier board is probably shorted.
• If 43 volts is found at TP5, check rectifier board connector J1 pin 6 for 43 volts DC. This is usually a brown wire (Bally) and goes directly to the playfield flipper coils.
  • Check rectifier board connector J3 pin 9 for 43 volts. This goes to the solenoid driver board connector J3 pin 5 for the flipper relay.
  • Check rectifier board connector J3 pin 12 for 43 volts. This goes to the MPU board connector J4 pin 15, and then to resistor R113.
  • Check rectifier board connector J3 pin 13 for 43 volts. This goes to the backbox on games that have a knocker in the backbox.
  • Check rectifier board connector J2 pin 2 for 43 volts. This goes to the lower cabinet for the coin lockout coils. Also goes to the knocker coil on games with the knocker in the lower cabinet. On early games this also goes to the chime unit.
• Locate the brown power wire at one of the flipper coils and check for 43 volts DC. If it is present at J1 pin 6 but not at any of the flipper coils, and then there is a wiring problem between the rectifier board connector J1 and the coils.
• If only the flipper coils work, than the 1 amp slow-blow under-the-playfield solenoid fuse is problaby blown. Or perhaps the brown wire from the flipper coils to the 1 amp fuse has broken.
• If the coils still do not work, check the solenoid driver board for 5 volts DC at TP3. If missing, look for a broken jumper wire on the solenoid driver board connector J3 that goes from pin 13 to pin 25.
• If only some coils works (in addition to the flipper coils), look for a broken yellow power wire under the playfield that runs from coil to coil.

Other possible (and more bizarre) problems if coils do not work:

• Possible problem with the game's ROM code that goes from the MPU connector J4 pins 5-8,10 to the solenoid driver board connector J4 pins 3-7. This code selects which of the 16 coils will fire. If one line is missing, coils 1 to 4 will not fire. Check MPU and solenoid driver board connectors J4 for broken wires or bad connector pins.
• Early A8 sounds boards AS2518-32 (games Lost World through Dolly Parton, though sometimes Star Trek to Dolly Parton will have a AS2518-50 sounds board) use the 43 volts. This sound board uses 43 volts DC to make 12 volts DC with a very crude voltage divider/regulator. Sometimes this sound board circuit fails and will short the 43 volts to ground. When trying to diagnose strange 43 volt coil problems in a games using the A8 soundboard, disconnect the power to the sound board before troubleshooting.
• If the 43 volts is missing from the whole game, then the MPU will not complete its 7th flash at power-up. This can be verified by checking for 43VDC on the left side of R113 (located below and to the right of the J4 MPU connector). If the 43VDC is present on the left side of R113 but there is no reading on the right side of the resistor, then replace R113 (2K ohms 1/4 watt). If both sides of R113 show 43 volts then the MPU board may have battery corrosion damaged and the whole area should be repaired.

Only Some Coils Work.


• Check is for power at all the coils in question. Using a DMM set to DC volts, put the black lead on the ground strap in the bottom cabinet of the game. Put the red lead on either lug of any coil. 43 volts DC should be seen. If power is only seen on one coil lug, the coil is bad. In no power is seen at either coil lug, check the power wire 'upstream'. Remember the 43 volts is daisy chained from coil to coil.
• If there is power at the coil, there could be a bad J4 connector (lower right) on solenoid board. A cracked solder joint on the solenoid board J4 header pins or a failed .100" terminal pin in the connector itself. Loosing contact with one of the signal lines can drop a bit, and the solenoid driver board can interpret the instructions incorrectly, firing the wrong coil or no coil at all.
• Bad Solenoid Driver board J4 (upper right side) or MPU board J4 (lower left side) connectors. A cracked solder joint on these header pins or a failed .100" terminal pin in the connector itself. Loosing contact with one of the signal lines can drop a bit, and the solenoid driver board can interpret the instructions incorrectly, firing the wrong coil or no coil at all. The encoding is sent to SDB connector J4 pins 3-6 (PB3-PB0 respectively) and SDB J4 pin 7 (CB2, solenoid bank select). This comes from connector MPU J4 pins 1-8 (PB0-PB7), which go thru resistors R97-R106, and then source at PIA U11 pins 10-17 (PB0-PB7). Any break in this connection stream will drop a bit and cause a solenoid to either not fire, or the wrong solenoid to fire.
• Bad decoder 74LS154 chip on solenoid board (or 74LS138 at U4 on Baby Pacman SDB), which mis-interprets the drive signals PB0-PB7 from the MPU board. This is the least likely problem but it does happen.

Locked On Coil Diagnostics.
If a coil is locked on (Burning! Turn the game off!) or doesn't work, there are several tests you can perform to isolate the problem. This is often seen with the game is first turned on (before the 7 MPU flashes finishes), a coil energizes and won't let go until the power is turned off. First it's good to know the sequence of events in energizing a coil:

• The MPU is told (by a playfield switch or other trigger) to fire a coil.
• The MPU turns on, for just a moment, a solenoid transistor on the solenoid driver board. This completes the power path to ground for the particular coil.
• The coil fires.
There are a series of steps you should take when a coil is not working properly, which we will outline below.

If a Coil is Locked On.
Generally, this is caused by a solenoid driver transistor that is shorted on. If a coil is locked on as soon as the game is powered on, turn the game off immediately (otherwise you'll be replacing more than a bad transistor!). Then follow these steps:

• Check the manual's schematics to figure out which transistor controls the coil in question. This information is on the Solenoid Driver/Voltage Regulator schematic page.
• Look at the connector in the center of the schematic. There the coil name/description will be listed.
• Follow this line back to the first "Q" (transistor) that intersects this line. Write down the transistor number (for example, "Q13"). Also write down the diode number behind it ("CR13"), and the chip number that drives this transistor ("U3"), and the pins of the chip (pins 11, 12). Also note the pin number that connects to the diode (pin 12). All these components could be damaged (but generally it's just the transistor).
Now that you know the transistor in question, you can test it.

Other Coil Diagnosing Techniques.
Another technique is to remove the solenoid connectors J1/J4/J5 from the solenoid driver board to the playfield. These connectors are on the left side of the solenoid driver board, and the one connector at the bottom right of the board too. Now power up the game (with good fuses), and install one connector at a time, until a fuse blows. Which ever connector blows a fuse, look for a little "spark" on one of the connector pins. Now go to the schematics, and see what coil that connector pin goes. Check that coil to make sure it has 2.5 ohms or greater resistance, the coil diode, and the coil's associated solenoid driver board transistor.

Remember there are two fuses that handle power for the coils. The 1 amp underplayfield slow blow fuse will usually only blow if a coil is energized and staying energized. Yet the power supply F4 fast blow fuse usually blows if there is a "hard short" (a dead-short across a diode, or coil that is shorted out (less than 2 ohms), or coil power is shorting directly against a metal ground).

Another thing is if fuse F4 blows, there is often a problem with the backbox knocker, or the cabinet coin door lockout coil, the solenoid bridge rectifier (on the rectifier board), or the rectifier board's varister.

Also try removing connectors J1 and J3 from the rectifier board (this moves the solenoid power back a step further, not allowing it to get any further than the rectifier board). Replace fuse F4 on the solenoid driver board, and turn the game on. If the fuse still blows, the solenoid bridge rectifier (on the rectifier board) or the rectifier board's varister is probably at fault.

Finally, disconnect a wire on each solenoid, and re-attach each wire, one at a time, until the F4 fuse blows. At this point it could be the coil, coil diode, or coil driver transistor at fault.

Testing the Solenoid board Transistors, Game Off.
The transistors on the solenoid driver board are very easy to test. This is done with the game off. You can remove the solenoid driver board, or leave it installed in the game. Using your DMM set to the "diode" setting, do the following:

• Turn the game off.
• On the component side of the board, put the black lead of your meter on the metal tab of a driver transistor.
• Put the red lead of your meter on the center lead of a transistor. Your meter should read zero.
• Put the red lead of your meter on either outside lead of a transistor one at a time. Your meter should read in the .4 to .6 volt range.
• Put the red lead of your meter on the other outside lead of the transistor. Your meter should again read in the .4 to .6 volt range.
If your meter reads anything outside the .4 to .6 range, replace that transistor.

Testing a solenoid driver board transistor. The black lead of the DMM is on the transistor's metal tab. The red lead is put on either outside lead, one at a time. The meter should read in the .4 to .6 range.

Testing a Solenoid board from the Transistor to the Coil, Game On.
If a coil is not locked on, you can test it's solenoid driver board from the transistor to the coil, with the game on and in "attract" mode.
• Attach an alligator wire and clip to ground in the backbox.
• Momentarily touch the other end of the alligator clip to the metal tab on a solenoid driver board transistor.
• The coil that is driven by that transistor should fire.
• Note this doesn't actually test the transistor itself, but just the path from the transistor to the coil.
• Optionally, you can also momentarily touch your ground wire to the solenoid board "U" chip; the pin that does NOT connect to the diode. This will also fire the coil.
If the coil doesn't fire, and the transistor tested properly in the above steps "Testing the Solenoid board Transistors, Game Off", you have either a blown playfield fuse or a broken wire/connector.

To test for a broken solenoid wire or connector pin, do this:

• Turn the game off.
• Put an alligator clip on the coil lug that the NON-banded side of the diode connects to.
• Connect the other end of the alligator clip to one of the test leads on your DMM.
• Set your DMM to continuity ohms setting.
• Refer to the manual and find the "J" connector number and pin number that the solenoid in question connects to on the solenoid driver board.
• Touch the other lead of your DMM to this "J" connector pin on the solenoid driver board.
You should get about 0 ohms. Note if you are testing to the wrong conector pin, you will get about 30 ohms.

Driver Transistor Tested Good, but Coil is still Locked On.
The driver transistor may be OK, but the 1N4004 diode behind it could be bad. Since we wrote down the diode that is behind the driver transistor (in the above steps), refer to that to get the diode number. Here's how to test it:

• Turn the game off.
• Remove the Solenoid driver board from the game.
• Put your DMM on diode setting.
• On the component side of the board, put the DMM leads on the 1N4004 diode. You should get a reading of .4 to .6 volts.
• Reverse the leads, and you should get the same reading you got in the previous step.
• BEST METHOD: remove one lead of the diode from the driver board, and retest. In one direction you should get a zero (null) reading.
If you get any other value, replace the 1N4004 diode.

Test the pre-driver CA3081 transistor chip. The picture on the left is testing the transistor pin that connects to the diode.

Now we need to test the chip that drives the diode and driver transistor. This chip is a CA3081 (NTE916) transistor array. Basically it's several transistors packaged in a chip format. This is known as the "pre-driver transistor pack". You can test this too:
• Turn the game off.
• Remove the Solenoid driver board from the game.
• Put your DMM on diode setting.
• On the component side of the board, put the black lead of your DMM on the GND test point just to the left of the U1 chip.
• Put the red lead of your DMM on the two pins of the pre-driver chip (one at a time) that you noted above.
• For the pin that connects to the 1N4004 CR diode, you should get a reading of .1 to .2 volts.
• For the other pin, you should get a reading of .7 to .8 volts.
• Reverse the DMM leads (red lead now on GND). You will get the same .1 to .2 volt reading for the pin that connects to the CR diode. The other pin will read 1.1 to 1.3 volts. Note this test is far less conclusive than the first test with the black lead on GND.
If you get any other meter readings, replace the pre-driver CA3081 (NTE916) chip.

Always Replace the SE9302 Transistor with a TIP102.
When ever replacing a bad SE9302 driver transistor, always replace it with the more robust TIP102. The TIP102 can handle more current and will just plain last longer.

Replace the Coil Diode and Driver Board Diode/330 Ohm Resistor.
If you had ANY problems with a coil being locked on, ALWAYS replace the coil diode. This 1N4004 diode prevents a "backlash" of current going to the solenoid driver board when the magnetic coil is shut off. This diode is easily damaged and can cause damage to your solenoid driver board if bad. Always make sure you install the new diode with the diode band on the "power" lug of the coil. The power lug is usually the lug with two wires going to it (because the power is daisy chained from coil to coil).

Likewise, on the solenoid driver board, also replace the associate CR diode that connects to the replaced driver transistor. This is also a 1N4004 diode. And it's a good idea to also replace the 330-ohm (1/4 watt) resistor that connects to this diode. Both of these components can really get toasted.

Testing for Power at the Coil.
If a coil doesn't work, and the transistor is good, test for power at the coil. Do this with the game on and in attract mode, and the playfield lifted.
• Put your DMM on DC voltage (100 volt range).
• Put the black lead on the metal side rail (ground) of the game.
• Put the red lead on either terminal of the coil. It should read about 43 volts. On flipper coils, any of the three terminals should also read about 43 volts.
If you are missing voltage at the coil, check for a broken wire/connector, or blown playfield fuse (see below). Remember the power wires are "daisy changed" together. So a break in the power wire in a previous coil will cause the coils further down the line to not work.

Testing a Coil.
You can also test a coil for proper operation. With the game on and in attract mode, and the playfield lifted, try this:

• Connect one end of a alligator clip and wire to the metal side rail of the game.
• Momentarily touch the other end of the alligator clip to the coil's terminal with the non-banded side of the diode connected to it.
• The coil should fire.
Note if you accidentally touch the banded side of the diode to ground, you will probably blow a fuse.

If the coil doesn't fire, you have a damaged coil or no power at the coil. Look for a broken wire going to the coil's terminal. You can also test the resistance of a coil. A good coil should be in the 3 to 15 ohm range.

The Over-Looked Under-Playfield Solenoid Fuse.
Often your Bally game will boot fine and start a game. The flippers work, but no other solenoids on the playfield work. This can often be caused by a blown under-the-playfield solenoid fuse.

If you run the solenoid diagnostic test and the coin lock-out coils, the flipper relay, and the knocker all work, and nothing else works, a dead under the playfield fuse could be the problem. Since the game boots OK, we know the +43 volt fuse on the rectifier board is OK (if this fuse was blown the MPU board won't "flash" the seventh time).

The under the playfield solenoid fuse is usually located on the right hand side by the flippers. Usually it's a 1 amp slo-blo fuse. If this fuse keeps blowing, you have a solenoid problem on the playfield somewhere. This can be caused by a shorted coil, a bad coil diode, or a broken (and shorted) coil wire. A shorted and locked on driver transistor is probably NOT your problem.

If the playfield fuse keeps blowing, there is another procedure you can try to isolate the problem as a last resort. Turn the game off and disconnect the "pull down" wire from EVERY coil under the playfield. The pull down wire is the single wire on each coil, and connects to the NON-banded side of the coil's diode (the power side connects to the banded side of the diode's coil lug). Then power the game on (the fuse should not blow!). Now re-connect each wire to its respective coil. When the fuse blows, you've found your problem coil/diode.

Coil TroubleShooting - More Ideas.
Here's some other ideas on coil problems.

No Coils Work.
• Check TP5 on the power supply for 43 volts. If no voltage, check fuse F4 on the power supply.
• Check solenoid driver board for +5 volts at TP3 on the driver board. If no voltage here, check for a broken jumper on connector J3 from pin 13 to pin 25.

Only the flippers work.

• Check 1 amp slow blow fuse underneath the playfield.
• Check for a broken wire from the above fuse. There should be a brown wire going from the under the playfield 1 amp fuse to the flipper coil.

Flippers work and just some coils.

• Under the playfield, check for a broken yellow wire from coil to coil. This is the coil power wire, and it daisy chains from one coil to another. A break in this wire will stop power from getting to coils "down stream".
• A problem with the connection between connectors J4 of the MPU board and J4 of the solenoid driver board. If one line is missing, coils 1 to 4 will not work.

Flipper does not work or are weak.


• Make sure the EOS (end of stroke) switch is filed clean & shiny with a metal file, and adjusted to be normally closed.
• EOS switch adjustment: When the flipper is fully energized, the EOS switch should open about 1/8". If this switch always stays closed, the flipper coil will burn. If the switch is always open the flippers will be very weak.
• File the cabinet switches with a metal file so they are shiny.
• Make sure the flipper coil wires that are part of the coil have not broken where they attach to the lugs. Remember a flipper coil is actually two coils in one package. The center lug is common, then one outside lug has a thick wire, and the other outside lug has a thin wire. There should also be two 1N4004 diodes on the flipper coil lugs. Often the thin wire will break away from the lug making the flipper "machine gun".
• Check the under playfield fuse and fuse holder. Often the fuse holder will be tarnished or have bad tension. Replace the fuse holder if in doubt.
• With the game on and in game over mode, use a DMM and measure for 43 volts DC at all three flipper coil lugs. If there is only power at 2 of the lugs, the flipper coil or EOS switch is bad. No power at any lugs check the fuses. Power for the flippers is "daisy chained" from other coils and sources. Sometimes the chain breaks "upstream". Look for that.
• Try grounding (momentarily) the center lug of the flipper coil in question - it should fire. If this makes a weak flipper strong, there is a bad ground path from the flipper to the flipper relay.
• Inspect the back of the Solenoid Driver board. The flipper ground path comes from the cabinet flipper switches to the SDB connector J1 (upper left connector). Then it goes to the flipper relay. Sometimes the circuit board traces from the connector J1 to the relay burn right off the SDB! Or the relay's solder joint and/or J1 header pin solder joints crack or go cold, causing the flippers to be weak or intermittent.
• Make sure the flipper relay energizes. If the flipper relay never energizes, the flippers will never work. The flipper relay should energize when a game is started or during the coil diagostic test. Also sometimes the contacts on the flipper relay can burn or pit.

Power supply board coil power distribution.

• J1 pin 6 = brown wire to flipper coils.
  
• J1 pin 9 = to solenoid driver board J3 pin 5 (flipper relay).
  
• J2 pin 2 = to chime unit (in early games) or knocker coil (in later games), and coin lockout coils in all games.
• J2 pin 13 = to backbox knocker on early games.
• J3 pin 12 = to MPU board connector J4 pin 15.

Wrong Coil (or No Coil) Energizes.
This is an interesting problem that isn't very easy to diagnose. For example when a slignshot switch closes, the drop target bank resets. Or perhaps one particular coil never engergizes in the game.

This is often due to the PB0-PB3 encoded lines that come from MPU PIA U11 or the line select. These four bits are encoded by the PIA, sent to the Solenoid Driver board (SDB), then unencoded by the SDB U2 74154 chip, and the appropriate solenoid is energized. If one of these four bits is lost in the data path between the MPU and the SDB, the unencoded number will be wrong, and the incorrect solenoid (or no solenoid) is energized.

Another test of this problem is to put the game in coil test. If coil(s) fire twice (same coil for two solenoid numbers), or does not fire at all, there is potentially a problem with the PB0-PB3 encoded lines.

The data path for this encoding starts at the MPU U11 PIA chip. Unfortunately this chip is right in the battery corrosion zone. So a bad U11 socket or broken trace is very common. Or if the MPU J4 pins 5-8,10 connector or SDB J4 pins 3-7 connector are bad (just one pin missing), the coil that gets fired will be decoded incorrectly by the SDB. Last the SDB U2 chip (74LS154) chip could be bad (though this is the least likely problem). Here's a list of things to check, and a table that will allow easy tracing of the PBx signals.

• Wrong game MPU ROMs installed - ROMs from another game installed at U2/U6.
• Bad U11 PIA on MPU board or bad socket for MPU U11 (which is in the "battery corrosion zone"). Swap PIA chips U10 and U11 to see if anything changes.
• Bad J4 pins 5-8,10 connector on MPU board (lower left corner). A cracked solder joint on the MPU J4 header pins or a failed J4 .100" terminal pin in the connector itself. Loosing contact with one of the signal lines can drop a bit, and the solenoid driver board can interpret the instructions incorrectly, firing the wrong coils. It's a good idea to use a DMM set to continuity, and "buzz out" the wire path from the MPU board to the Solenoid driver board. This should be done with the connectors in place, so any connector issues are identified. (That is, measure continuity from the MPU board components R97-R100 to the SDB component U2, inclusive of the connectors. See the table below for help with that.)
• Bad J4 pin 3-7 connector on solenoid board (upper right corner). Again a cracked solder joint on the solenoid board J4 header pins or a failed J4 .100" terminal pin in the connector itself.
• Swapped wires on the MPU board's switch matrix connector from a previous repair.
• Bad decoder 74LS154 chip on solenoid board, which mis-interprets the drive signals.
• Short from solenoid power (43 volts DV) to a switch matrix line (12 volts DC) somewhere under the playfield. This is sometimes seen on games with three or six bank drop target assemblies. The drop target units have a daisy-chain of 43 volts DC that go from coil to coil on the drop target unit (and sometimes to small memory or knock-down coils). It is very common that the wiring wears from rubbing on metal and eventually shorting 43vdc to the whole metal chassis of the target unit. This can cross over to the switch matrix lines from the switches touching the arms at the bottom of each drop target. A quick check is to unplug the wiring harness connector that connects to drop target bank assembly, and re-boot the game.

Note that PB0-PB3 are the encoded "momentary" solenoid lines, and that CB2 is the bank selection bit. That is PB0 to PB3 are the bits that get encoded and unencoded. There is also PB4-PB7 which are "continuous" solenoid lines (these usually control the coin lockout coil, flipper disable, and potentially two other coils). These bits don't get encoded, and control coils directy from the PIA (they don't go thru the SDB 74154 chip).

Note on Baby Pacman things are a bit different. First only PB0-PB2 are encoded. PB3 and PB7 are not used. PB4-PB6 are the continuous solenoid lines. Also the SDB connector is different: J9 pins 7,6,5 are PB0-PB2 respectively. J9 pin 4 is CB2 (solenoid select bank). J4 pins 10,9,8 are PB4-PB6 respectively. SDB U4 (74LS138) does the signal decoding (but again, this is the least likely problem).

When the wrong coil (or no coil) energizes, I find it best to first trace the PB0-PB7 lines from the MPU U11 PIA to the Solenoid Driver board.

PBx	Signal Type	PIA U11	MPU Resistor	MPU J4	SDB J4*	SDB U2 (74154)*
PB0	Momentary (encoded)	U11 Pin 10	R97 (470 ohm)	MPU J4 pin 4	SDB J4 pin 6	U2 pin 23
PB1	Momentary (encoded)	U11 Pin 11	R98 (470 ohm)	MPU J4 pin 3	SDB J4 pin 5	U2 pin 22
PB2	Momentary (encoded)	U11 Pin 12	R99 (470 ohm)	MPU J4 pin 2	SDB J4 pin 4	U2 pin 21
PB3	Momentary (encoded)	U11 Pin 13	R100 (470 ohm)	MPU J4 pin 1	SDB J4 pin 3	U2 pin 20
PB4	Continuous (not encoded)	U11 Pin 14	R101 (330 ohm)	MPU J4 pin 5	SDB J4 pin 11	n/a
PB5	Continuous (not encoded)	U11 Pin 15	R102 (330 ohm)	MPU J4 pin 6	SDB J4 pin 9	n/a
PB6	Continuous (not encoded)	U11 Pin 16	R104 (330 ohm)	MPU J4 pin 7	SDB J4 pin 8	n/a
PB7	Continuous (not encoded)	U11 Pin 17	R105 (330 ohm)	MPU J4 pin 8	SDB J4 pin 10	n/a
CB2	Coil Bank Select	U11 pin 19	R106 (470 ohm)	MPU J4 pin 10	SDB J4 pin 7	U2 pin 19

* This table's SDB info does not apply to Baby Pacman, Granny & Gators, Grand Slam.

Bally's lamp driver and auxiliary lamp driver boards stayed pretty consistant from 1977 until 1989 (when Bally produced its last game, before being taken over by Williams). These procedures should work on all Bally lamp driver boards from their inception until their end in 1989.

The power for all CPU controlled lamps comes from the rectifier board through fuse F1. On pre-Xenon games (transformer in the backbox), 7 volts AC comes from the transformer to a 10 amp fuse, through a 8 amp bridge rectifier (converted to 6 volts DC), and then to all of the playfield's CPU controlled lamps (there is a lamp power buss wiring going to all CPU controlled lamps under the playfield). On Xenon and later games, it works the same way but the bridge rectifier is larger and so if the F1 fuse (20 amp). The lamp driver board is really a misnomer, as the lamp driver board drives nothing. It has a SCR (Silicon Controlled Rectifier) for each of the CPU controlled lamps. The SCRs switch ground on and off based on decoded information from the MPU board. This completes the power circuit to that particular CPU controlled lamp, turning it on.

If a feature light is continually on, or is never on, you can test the lamp driver board for a component problem. Assuming the wiring is intact, chances are good that the lamp's driving component(s) are bad. This is especially true if a lamp is always on. The internals to the driving components have probably shorted on, leaving the lamp continually on.

All Bally electronic pinball games until Williams bought them out in 1989 used SCR's (Silicon Controlled Rectifiers) to drive feature lamps. SCR's are different than transistors. Instead of a collector, base and emitter like a transistor, they have a cathode, anode and a gate (abbreviated C, A, G respectively, though sometimes the "C" is abbrevated as "K"). Each gate is driven by a CD4514 CMOS decoder output. All SCR cathodes are connected to the feature lamp ground. Each SCR anode is connected to a unique feature lamp.

There are two different SCR's used for lights on the lamp driver board: the larger MCR106-1, and the smaller 2N5060. They serve the same function, just the larger MCR106-1 can handle more current (and sometimes lights two lamps, while the smaller 2N5060 can only light one lamp). There is also a CD4514 CMOS decoder that drives the lamps. Sometimes these go bad too.

Why No Lamp Matrix?
Bally didn't use a lamp matrix like Williams did. Bally's approach was more like Gottlieb's system80, where there was a single transistor or SCR that drives each lamp. There are a total of 24 of the larger MCR106 SCRs, and 36 of the smaller 2N5060 SCRs. This gives a maximum total of 60 discrete CPU controlled lamps in a typical Bally game (the MCR106 could actually control two lamps at the same time, but I count that as one discrete lamp). Some game also had an Auxilary Lamp Driver board which allowed for more than 60 CPU controlled lamps. Because there are 60 lamps and 60 SRCs and no lamp matrix, there are 61 wires going to all the CPU controlled lamps (one power wire, and then a single control wire for each of the 60 lamps). Connectors J1 and J3 on the lamp driver board have 28 pins each, meaning potentially 56 wires go to the playfield for the CPU controlled lamps. The remaining CPU controlled lamps go to the backbox through connector J2 for (at minumum) the Game Over, Tilt, Match, High Score to Date, and Ball in Play lamps, and some other lamps.

Power to the Lamps?
All the playfield CPU controlled lamps have 6 volts DC going to them from the transformer's rectifier board. If none of the CPU controlled lamps work, usually this is a blown rectifier board fuse, bad rectifier board connector, and/or bad rectifier board bridge.

On the bottom of the playfield you will notice a bare wire going to all the CPU controlled lamps. This is the Positive lead of the 6 volts for the lamps. Then on the Tip of each socket there is a color coded wire. This wire goes to the lamp driver board, which grounds this wire, turning the particular lamp on. If none of the lamps work, using a DMM set to DC volts, check the bare playfield wire and make sure there is 5 to 6 volts DC power for the lamps. If not, go to the rectifer board and find why there's no power to the lamps.

Diagnosing Non-Working CPU Controlled Playfield Lamps.
Start the diagnosis by putting the game into the first diagnostic test by pressing the Red test button inside the coin door. This will make all the CPU controlled lamps flash on and off. Note if the game has a Solenoid Expander board under the playfield, this board will turn it's relay on and off, and its accompanying 555 lamp will flash too.

First make sure that a non-working playfield lamp's SOCKET is not the problem! Bally lamp sockets are really crappy, and most non-working lamp problems are related to the socket. Remove the bulb and put it into an empty backbox socket as a test of the bulb. If the bulb is Ok, put it back in the playfield socket and twist it a couple times. Often this will make a non-working lamp turn on. If you want a more permanent solution to a lamp that doesn't want to stay working, either replace the socket with a new one, or solder the socket (as shown in the picture below).

"Fixing" a playfield lamp socket. The wire that powers the tip of the bulb is moved directly to the tip of the socket. The base of the socket is then soldered together so it can not rotate. Be sure to sand the parts before soldering, and to use some Rosin flux on the socket.

If the lamp still does not work, I use a logic probe to see if the lamp is really being driven by the lamp driver board. I know most people don't have a logic probe (but you should, as they are only $20), but it really is a good way to see what is going on. Put the logic probe on a WORKING lamp socket's TIP, and notice how the signal pulses. Now put the logic problem on the Non-working lamp socket's tip, and compare. Is the signal the same? If so, you have a socket problem. If the signal is different, then it's time to move up to the lamp driver board for more diagnosis.

Start by making a list of the non-working lights. If you don't have the schematic, list the non-working lamps AND their wire color that connects to the lamp socket's tip. Now go to the lamp driver board and find the connector with that wire color (game off). Using a DMM set to continuity, you can verify that you have found that wire's connector pin on the lamp driver board. Use a Sharpie pen and mark that pin on the lamp driver board.

Remove the lamp driver connectors, and look at the .100" molex female connector pin in the housing. Sometimes these pins break, and this may be the only problem. Otherwise remove the lamp driver board from the game, and look at the male .100" connector pin. Another common problem is the solder joint of the male connector pin to the board cracks. Touching up the solder at this pin again often fixes a non-working lamp. CAREFUL though, as it is very easy to bridge solder across two pins (these .100" connectors are small and the pins are close together).

Lamp still doesn't work? At this point i use the DMM set to continuity, and find the SCR on the lamp driver board that connects to the male pin for the non-working lamp. Mark the SCR with a Sharpie, then change the DMM to diode function. Using the diode test, the SCR can be checked against a working SCR next to it, to see if the suspect SCR is bad. If the SCR is suspect, replace it. At this point, nearly all non-working lamp problems should be handled by this methodology. (If a lamp or set of lamps still doesn't work, keep reading below.)

Lamp board decodes for 8 Ball Deluxe U1 chip in blue box.

More Complicated Lamp Problems.

AD0-AD3 Lamp Data Lines and PD0-PD3
(or Mass Amounts of Non-Working Lights).
If a particular game has lots of non-working lights, this could be related to a connector issue. To really understand this problem, one must know how the Lamp driver board decodes the lamp info from the CPU board.

There are four lamp data lines (AD0-AD3) which ultimately decide to which lamp gets turned on. These four data lines are binary in nature. That is, they can be 0 or 1, and the combination of these four lines decodes to 16 different binary values. (There is also a toggle line PD0, which is the bit that actually turns U1 chip 'on'.) The AD0-AD3 lamp data lines get decoded by the four 4514 chips on the lamp driver board, and ultimately go to each of the SCRs and to each of the lamps.

For example, below is an Eight Ball Deluxe lamp driver schematic. Now say you run the game's lamp diagnostic test and find a bunch of non-working CPU controlled lamps (Rack 9-15, Target 9-15, "D E L U", 20k,40k,60k saucer values, 50k,70k, 2x,3x,4x,5x,56k,112k bonus values, special saucer, special left lane, shoot again). And the pop bumper lights are always on but go bright/dim/bright/dim. So how do you figure out what is wrong?

Go to the lamp driver schematic and mark all the non-working lamps. Sometimes a pattern can be seen where the lights that don't work are always lamp driver values 2,3, 6,7, 10,11 for all four U1-U4 decoding chips (for now forget about the Aux Lamp Driver board used in 8 Ball Dlx). It's important to remember that AD0 is the right most bit, and AD3 is the left most bit. With this in mind, looking at the binary values for these six missing lamp numbers, another pattern can be seen. That is, the AD1 line (second bit from the right) is always "1" on these six missing lamp lines binary numbers.

Knowing this, we can conclude that the AD1 line going to the lamp driver board is probably broken (or stuck low at the MPU board, meaning a PIA problem). But most likely this is a bad connector pin at the MPU J1 connector (J1-15=AD0, J1-14=AD1, J1-13=AD2, J1-12=AD3). Or at the lamp driver board J4 connector (J4-14=AD0, J4-15=AD1, J4-16=AD2, J4-17=AD3). In this case, because some of the missing lamps are driven by the Auxiliary Lamp Driver board, the problem is almost for certain at the MPU board J1 connector.

There is one more consideration, that is the PD0-PD3 lines. Remember the lamp data AD0-AD3 decodes value from 1 to 16 (in binary). But there are also four PD0-PD3 lines that tell the lamp driver board which U chip the AD0-AD3 lamp data is for. For example say PD2 is toggled. That means lamp data AD0-AD3 applies to the U3 chip (and the lamps which are controlled by the U3 chip). So if you have 16 lamps that don't work and they are all controlled by a single lamp driver U chip, it's most likely a problem with the corresponding broken PD line (PD0 for U1, PD1 for U2, PD2 for U3, PD3 for U4).

The last issue to think about is this: coin door switches. Now normally you would think this has nothing to do with lamps, but it does. If the coin door switches are shorted to the metal coin door skin (ground), or the insulating fishpaper behind the start button is gone (shorting this switch to ground), this can cause all sorts of strange behavior. Like the same type of problem as one of the AD0-AD3 lamp lines missing, where numerous lamps may not work. A quick test of this is to remove MPU connector J3 (lower right). If problems clear, a shorted coin door switch is definately the problem.

Left: the -23 Lamp Driver board with no 4050 buffer chips. Right: the earlier -14 Lamp Driver board with 4050 buffer chips. Bottom: Stern's LDB-100 Rev B lamp driver board. All three of these lamp driver boards are interchangable with each other.

Two Different Lamp Driver Boards.
Bally had two different lamp driver boards, the AS-2518-14 and the AS-2518-23. Both boards have the same number of SCRs, and are completely pin compatible and either board will work in any 1977-1985 Bally solidstate game. The only difference is the earlier -14 Lamp Driver uses four CD4050 buffer chips between the MCR106 SCRs and the CD4514 decoder (the smaller 2N5060 SCRs did not use a buffer chip). But Bally found the lamp driver board to be so robust that the CD4050 buffer chips were not needed. Therefore the -23 version of the Lamp Driver board has just four CD4514 chips and 60 SCRs, with no CD4050 buffer chips. The -14 lamp driver board was only used for from 1977 to 1978 (for example Freedom to Power Play used the -14, but Mati Hari used the -23) when it was replaced by the -23 lamp driver board. The -23 lamp driver even has silk screened on the board, "replacement for AS-2518-14". Even though the -23 board is larger, it was cheaper to produce than the earlier -14 board. The reason was the -23 board is a single-sided board, with circuit board traces only on one side (this is cheaper to make compared to a two-sided board). All the "jumpers" seen on the -23 are not user changable - they are required to move a board trace around other traces on the single-sided board.

Replacement SCR's.
Replacement SCRs are available from a variety of sources. For example, Jameco sells the MCR106-1 as part number C106Y or C106B1, and NTE5411 to NTE5416. The smaller 2N5060's replacement number is 119802 or NTE5400 to NTE5406 (but the NTE version is much more expensive) or at Mouser part# 610-2n5060. Also the larger MCR106-1 can be used in place of the smaller 2N5060, but only if the "A" and "G" legs are "reversed" (twisted to be reversed, when installed). This is not recommended, but it can be done in a pinch.

Mounting a MCR106.
There are many styles of MCR106 rectifiers. When mounting the style without the metal face, note the ANGLE side and the mounting orientation. The angle sided C106 seems to mount "backwards", compared to the metal faced version of the MCR106 (because the manufacturer writing seem like it is on the back of the angled sided SCR). See the picture below.

Mounting of the two styles of MCR105 rectifiers. Note the angled sided SCR compared to the metal faced SCR.

The two styles of SCRs used in Bally games. Left: the SCR106-1. Right: the 2N5060.

This table (thanks to S.Kulpa) shows which SCR goes to
which connector number on any of the lamp driver boards.

SCR Connector Q1 J1-24 Q2 J1-25 Q3 J1-26, J2-21 Q4 J1-28 Q5 J2-16 Q6 J2-14 Q7 J1-27, J2-13 Q8 J1-23 Q9 J1-14 Q10 J1-15 Q11 J1-16 Q12 J1-19 Q13 J1-17 Q14 J1-18 Q15 J2-23

SCR Connector Q16 J2-22 Q17 J1-11 Q18 J2-20 Q19 J2-15 Q20 J1-13 Q21 J1-12, J2-12 Q22 J1-10 Q23 J1-4, J2-8 Q24 J1-5 Q25 J1-6 Q26 J1-7 Q27 J1-9 Q28 J1-8 Q29 J1-1 Q30 J2-6

SCR Connector Q31 J2-2 Q32 J3-27 Q33 J2-11 Q34 J1-2 Q35 J1-3 Q36 J3-26 Q37 J3-23 Q38 J3-25 Q39 J2-4, J3-24 Q40 J2-9, J3-22 Q41 J3-20 Q42 J3-21 Q43 J2-7 Q44 J3-19 Q45 J2-1

SCR Connector Q46 J3-18 Q47 J2-10 Q48 J3-16 Q49 J3-17 Q50 J3-12 Q51 J3-15 Q52 J2-5, J3-13 Q53 J2-3, J3-14 Q54 J3-11 Q55 J3-9 Q56 J3-10 Q57 J3-1 Q58 J3-2 Q59 J3-4 Q60 J3-3

Testing the Lamp Driver SCR's, game On.
If a lamp is permanently stuck on, this procedure won't tell you anything. A lamp that is always on is generally caused because its SCR has internally shorted. Replace the SCR.

Assuming the game powers on, you can test a non-working lamp's SCR's to see if it's working (this assumes you have checked the bulb, the lamp socket, and the wiring to the lamp socket).

• While the game is on and in "attract" mode, press the Self-Test button inside the coin door ONCE. This should put the game into the "Flash All Feature Lamps" test (check your game manual if it does not).
• Note which feature lamps are NOT working. The Bally self test will flash ALL sixty lamps without exception. Write down which lamps do not flash. (You will need this information if several lamps that connect to the same decoder don't work. A decoder has likely failed if 4, 8 or 12 lamps, multiples of 4, are not working.)
• Check the manual's schematics to figure out which SCR number controls the lamp(s) in question. This information is on the Lamp Driver schematic page.
• Look at the connectors at the right of the schematic. There the lamp name/descriptions will be listed.
• Follow this line back to the first "Q" (SCR) that intersects this line. Note the SCR number (for example, "Q8"). If the schematic lists a "**" next to the SCR, this means it's a MCR106-1. Otherwise it's a 2N5060. Also note the chip that drives this SCR (U1 to U4). Both these components could be damaged (but generally it's just the SCR).
• Write down the "Q" number and the lamp name on some paper. Also write down the driving decoder "U" chip number.
• If 4, 8 or 12 lamps that all connect to a single decoder don't work, suspect the decoder "U" chip as faulty.
• Press the game's test switch again to take the game out of lamp test mode. The display test will probaby come up. Leave the game here, as all the playfield lamps should now be turned off.

• With the game in display test, connect an alligator test lead wire to ground. The bare braided wire in the bottom of the back box works well for this.
• Touch the other end of the test lead to the ANODE (A) of the SCR in question. On the larger MCR106, the metal face or metal tab is the anode. On the smaller 2N5060 SCRs, it's the lower right leg. To make sure, the pinout for the SCRs is silk screened on the board for a few selected SCR. Look for the lead marked "A".
• If the lamp does NOT light when the anode is grounded, the problem is NOT on the lamp driver board. Most likely you have a wiring problem, a bad lamp socket, or a bad bulb.

Lamp Always Off.


1. With the game on and in score display test mode, connect one end of an alligator jumper to Lamp Driver board TP3 (goes to R70 2k ohms).
2. Connect the other end of the alligator jumper to the GATE (G) of the SCR in question. On the larger MCR106, this is the left leg. On the smaller 2N5060, this is the right side (center) leg.
3. The lamp in question should light.
4. If the lamp does not light, the SCR is probably bad. Test the SCR with the power off using a DMM in diode test, as described below. If the SCR tests bad, replace it. Repeat steps above 1 to 3.
5. MCR106 and -14 lamp driver board only: If the MCR106 tests good on a -14 lamp driver board with buffer chips, replace the CD4050 buffer chip connecting to the MCR106 in question. Repeat steps above 1 to 3.
6. If the lamp still won't light, replace the 4514 decoder chip connecting to the SCR in question. Repeat steps above 1 to 3.

Lamp Always On.


1. With the game on and in score display test mode, connect one end of an alligator jumper to Lamp Driver board TP2 (ground).
2. Connect the other end of the alligator jumper to the GATE (G) of the SCR in question. On the larger MCR106, this is the left leg. On the smaller 2N5060, this is the right side (center) leg.
3. The lamp in question should turn off.
4. If the lamp does not light, the SCR is probably bad. Test the SCR with the power off using a DMM in diode test, as described below. If the SCR tests bad, replace it. Repeat steps above 1 to 3.
5. MCR106 and a -14 lamp driver board: now ground the input leg of the CD4050 connecting to the SCR in question. If the lamp does not go out, the buffer chip is bad. Repeat steps above 1 to 3.
6. If the lamp still won't go out, replace the U chip connecting to the SCR in question. Repeat steps above 1 to 3.

Testing the Lamp Driver SCRs POWER OFF.
You can also check the lamp driver board's SCR's using your DMM, set to the diode setting.

• Check the manual's schematics to figure out which SCR controls the lamp(s) in question. This information is on the Lamp Driver schematic page. Write down the SCR's "Q" number.
• Look at the connectors at the right of the schematic. There the lamp name/descriptions will be listed.
• Follow this line back to the first "Q" (SCR) that intersects this line. Note the SCR number (for example, "Q8"). If the schematic lists a "**" next to the transistor, this means it's a MCR106-1. Otherwise it's a 2N5060. Also note the chip that drives this SCR ("U1"). Both these components could be damaged (but generally it's just the SCR).
• You can remove the lamp driver board, or leave it installed in the game. Use your DMM set to the "diode" setting.

MCR106-1 Lamp Driver SCR test:

• Put the black lead of your meter on the outside "cathode" leg (labeled "C") of the SCR.
• Put the red lead of your meter on the outside "gate" leg (labeled "G") of the SCR. Your meter should read .4 to .6 volts.
• Swap the meter leads. Now the meter should read 1.4 to 1.6 volts.
If your meter reads anything outside t