Troubleshooting Williams Bally WPC Pinball Machines

A. Caution
B. Solid State Troubleshooting
    1) Early Bally / Stern
    2) WPC Bally / Williams
    3) Williams 11
    4) Williams 3 – 7
C. EM‘s

This covers all WPC pinball machines made by Williams and sold from 1990 to 1999 under the Williams and Bally names. 
This includes:  WPC 1990 – 1991 (Alpha Numeric), WPC 1991 (Dot Matrix), WPC 1992 (Fliptronics 1), WPC 1992 – 1994 (Fliptronics 2), WPC 1993 – 1994 (DCS), WPC-S 1994 – 1995, and WPC-95 (1995 – 1998)

All of these machines use the same power supply / driver board, except WPC-95, so be certain to know which board applies to your pinball machine.

Prior to starting, check the tools required and cautions.  

Understanding the Layout

The common circuity is located in the backbox as shown in the picture.  Not all boards are in all machines.  Early alpha numeric machines did not have a DMD board.  And Fliptronics was introduced with The Addams Family.  More complex machines added boards under the playfield, usually for optical switches (optos) and some motors.  The power transformer and a power filter box are located below, in the cabinet.

WPC89 Fliptronics is shown in the first picture.  But all WPC89 machines have a similar layout.  Alpha Numeric machines lack DMD and Fliptronics boards, early DMD machines lack Fliptronics boards, and WPC-S is essentially the same as WPC89, with the only change in the components on the CPU board.

WPC95 has a completely changed layout.  And the plug numbers on the boards are also different.

Voltages Required

All pinball machines require certain voltages to be present in order to work and WPC is no different.  There must be +5, +12  and ground present on the CPU board.  Other boards such as display, sound and Fliptronics require other voltages.

When experiencing problems, the first step is ALWAYS to check for proper voltages.  Without being certain that the voltages required are present, you cannot properly troubleshoot a pinball machine.

There is always the hazard that the voltages will be too high and a board can be damaged.  With Williams WPC, while that possibility is quite remote, it may be wise to disconnect the power to the other boards and concentrate on the power supply by itself.

We usually take a fine Sharpie and mark the plugs on their side with the plug number. But these plugs (should be) keyed and they are difficult to mess up.

Many of these connectors may not have a plug in them and do not require any action.

Power Driver Board

The Power Driver Board is the largest board in the backbox.  It serves two functions: 1) convert the AC from the transformer to DC used by the other board, and 2) control (or ‘Drive’) the solenoids, flashers and light bulbs.

What can go wrong

1) Connectors (header pins and plugs), wires.
2) Board problems – voltage regulator, capacitors, rectifiers, etc.  Check to see if any look burned or discolored.  If they do, replace both the pins and the plugs.
3) The +5 is the most problematic on WPC89 and WPC-S.  Issues with the regulator, bridge and large filter capacitor are the most common .
4) Less common are issues with the +12 (digital).

Many of these problems can be easily fixed.  The voltage regulator is easily replaced.  Replacing the large electrolytic capacitors and the bridge rectifiers requires advanced desoldering / soldering skills.  Many of these boards have been damaged during attempted replacements, so this should not be attempted by beginners.

Note that the WPC95 power supply is far more reliable than the WPC89 & WPC-S power supply.  But with age, this can fail too, especially as the electrolytic caps get old.

To Isolate the Power Supply (Optional)

For WPC89 and WPC-S:

With the power off, on that big board, unplug the following:
J120, 121, 119 (GIs)
J109, 110 (maybe empty since this is Fliptronics)
J107, 106, 108 (solenoids)
J104, 105 (AC goes elsewhere, like Fliptronics)
J114 (+12 & +5 digital)
J118, 117, 116 (+12 & +5 digital)
And:
J605 (on DMD driver. AC going in there.)
J501 (AC going in there.)
 
For WPC95:
With the power off, on that big board, unplug the following:
J106/J105/J104 (GIs)
J119 (Flipper Power)
J133/J134/J135 (Solenoids and Flashers)
J130/J131 (AC out to other boards)
J101 (+12 digital and +5)
J138/J139/J140/J141  (+5 and +12 unregulated)
And:
J605 (on DMD driver.  AC going in there.)
Power Driver Board Voltage Readings

You should read the following DC values on the Power Driver Board.  Except for the 5V, they don’t have to be exact.  When possible, connect the black lead to ground on this board.  Note that there are LEDs on these boards that confirm if a voltage is on.  But these LEDs do not give voltage, so using a DVM is better.

WPC89 & WPC-S

WPC89 Power Driver Board
WPC89 Power Driver Board

TP1 = +12
TP2 = +5 (between 4.9 and 5.2)
TP3 = +12 Digital (check AC here, too.)
TP4 = not important here
TP5 = is ground
TP6 = 50 (it likely will read ~70)
TP7 = 20
TP8 = +18 (Lamps)
 
WPC95
 
WPC95 Power Board
WPC95 Power Board

TP100 = +12 (should be very close to +12)
TP101 = +5 Digital (should be very close to +5)
TP102 = +18
TP103 = +12 (unregulated – can vary)
TP104 = +20 (it likely will read higher)
TP105 = +50 (it likely will read ~70)
TP106 = not important here
TP107 = is ground
 
If all of these voltages read OK, then plug back in the removed plugs – the problems are not due to power supply issues (unless the voltages drop under load).  
If any voltages are out of spec, move onto troubleshooting the power supply.
 
Troubleshooting the Voltages

For WPC89 and WPC-S

If the +12 is good at TP1 (as low as 10 V DC or so), but the +5 is low or absent, then the LM323 is likely defective and should be replaced.  Or better, replaced with the EzSBC modern equivalent.

Check the large electrolytic ‘cans’ for leakage or deformity.  The top should be flat.  If not, replace them.

If the voltages are low, it maybe the capacitors or the bridge rectifier BR2.  If BR2 shorts, fuse F113 will blow.  If one or more of ‘sides’ of the bridge fail open, then the +12 at TP1 will drop.  Test BR2 with the diode tester and J101 removed.

Less likely are issues with +12 (Digital) at TP3 or +18 at TP8.   If TP8 is good, then the voltage regulator LM7812, Q2, has likely failed.  If the +18 at TP8 is low, suspect the bridge BR1 or the large caps C7 & C6.

For WPC95

Less likely are issues with +12 (Regulated) at TP100 or +18 at TP102.   If TP102 is good, then the voltage regulator LM7812, Q2, has likely failed.  If the +18 at TP8 is low, suspect the one of the diodes D11 – D14 or the large caps C11 & C12.

If TP103 is low, it should be one of the diodes D3 – D6, or C8. 

If TP101 is low, check the output of the diodes D7 – D10 (the banded side of D9 or D10), or the + side of C9 – there is not a test point here and this may be hard to check.  If this is about +12 V, then the voltage regulator Q1 LM317 has likely failed.   

Other Board Voltages

You have plugged back in the Power Driver Board and it still does not work.  There could be other boards involved:

DMD Driver Board – For DMD machines – if your display is not working.
Fliptronics Board – WPC pinball machines from The Addams Family on (~1992) have this board.
Sound Board – If your sound is not working, start here.
CPU Board – The CPU does not create its own power, but it has to get there for it to boot.

CPU Board

The power comes in J210 in all models.  Unfortunately, there are not convenient test points to confirm the voltages.

It is always best to use the ground on the board under test.  On the CPU, this takes a little creativity.  On J210, pins 1 & 3 are ground.  If you have a clip lead with a hook, unplug J210 and put the hook around pin 1, towards the outside, then push J210 all the way back on.   Otherwise, the screws holding the board in place should be grounded.  

Alternatively, the (-) minus side of C31 is ground and the (+) plus side of C31 is 5 V DC.

What can go wrong

Not much, and a whole lot.  This is generally a reliable board as long as you don’t let the batteries leak.  Or put solenoid voltage into the switch matrix.  And a few other things.  

But the board cannot boot if the voltages and ground are not present.

J210 Voltage Tests

Capacitor 31 WPC CPU
C31, to the right of the battery holder WPC89 & WPC-S.
WPC95 CPU with C31
C31 on the WPC95 CPU

Pins
1,3 – ground.  The (-) side of C31 can also be used.
4, 5 – +5 (4.9 – 5.2).  The + side of C31 can also be used.
6, 7 – +12

Troubleshooting

If the voltages are good on J210, including ground (this is important), then the CPU is likely defective.

DMD Driver Board (WPC 89 and WPC-S)
Audio Visual Board (WPC95)

For those games with a DMD (digital matrix display), it will not work without this board working properly.

Note, this board has extremely high and dangerous voltages.  Prior to proceeding, read all of the cautions.  

This board requires +5 and +12 V DC from the Power Driver Board via J606.  But it also receives AC directly from the transformer and converts it to high voltages at J605. 

Note that WPC95 combined the DMD board with the audio board.   WPC89 and WPC-S has a separate board.  The following applies only to the ‘Visual’ part of the WPC95 board.

There are two sections to this board: high voltage supply, and, the digital driver section.  We are only going to check the high voltage section.  

What can go wrong

1) The high voltage section of the Williams WPC board is prone to overheating and component failures.
2) Board problems – voltage regulator, capacitors, rectifiers, etc.  Check to see if any look burned or discolored.  If they do, replace both the pins and the plugs.

Voltage Tests
power test points
DMD Power Plug

The easiest place to test these voltages are not on this board, but on the display itself.  The display has pins that are bent at a 90 degree angle from the board.  That makes access to those pins rather easy.  

Note: It is important to not accidentally short one pin to the other when taking these readings.

All DMDs use this same plug.  The #1 pin is on the left.  It would be better to use a ground on this board, but if not easily attached to, use the Power Driver Board ground, or another available ground.

Pin Measurements (all V DC):

#1 = – 120
#2 = -108
#3 = key, N/A
#4&5 = Ground (read nearly zero vs. Power Driver Board, but may get a very low reading) 
#6 = +5 (4.9 – 5.2)
#7 = +12
#8 = +60

Troubleshooting

The +5 and +12 volts come from the power driver board.  If they are absent here, but present at the Power Driver Board, it is likely a connector.  There are a few components for +12 that could go bad, but this is unlikely.

#1 and #2 can vary a little bit from these readings, but there must be a 12 volt difference between them.

If pins #1, #2 or #8 are wrong, either rebuild the power supply or replace the board.

Fliptronics Board (WPC89 & WPC-S only)

Fliptronics 2 Power Supply
Fliptronics 2 Power Supply

WPC pinball machines use the Fliptronics technology from The Addams Family, on.  The Addams Family was the only one where two boards were used, the second board to create the 50 V DC for the flippers.  All other machines used Fliptronics 2 that had the 50 V power supply built in.  Fliptronics 2 also has the coil diodes built into this board, a major advantage.

If your flippers are not working, it could be this power supply.  Note that for The Addams Family, the +50 volts is done on the the power supply board for Fliptronics 1.

This board also receives +12, +5 and ground from the Power Driver Board, via J904 and cannot operate without those voltages and ground.

What can go wrong

The AC comes into the Power Driver Board and then back out to the Fliptronics Board.  This Fliptronics board consists of a bridge rectifier to convert the AC to +50 V DC, and fuses for each flipper.   If the bridge rectifier goes bad (shorts), F112 on the Power Driver Board will blow.

If one of the fuses blows on this board,  either the flipper coil is damaged or one of the TIP 102 or TIP36C transistors is shorted.

Voltage Tests

Set  your DVM to V DC.  Connect the black lead to any ground.  Touch the red lead to each side, one at a time to fuse clips F901 – F904.   Both sides of each fuse will likely read higher than the 50 V, because there is not a load.  70 V DC is common.

There are not any test points on this board to confirm +5, +12 and ground.  But C1 is a good place to check +5 and ground.   Connect your black lead to ground on the Power Driver Board TP5.

C1 (+) side = +5 V DC (same as +5 on the Power Driver Board).
C1 (-) side = ground (read nearly zero vs. Power Driver Board, but may get a very low reading).

Troubleshooting

+50 V DC 

Note that there is not a fuse on the Fliptronics 2 board before the bridge rectifier.  That means if this bridge is bad, then fuse F112 on the Power Driver Board will blow.  The problem with this setup is that if F112 blows, it could be a shorted bridge BR3 on the Power Driver Board, or bridge BR1 on the Fliptronics 2 board.  The way to troubleshoot this is to unplug J901 and replace F112.  If F112 blows, it is BR3 on the Power Driver.  If F112 does not blow, it is BR1 on the Fliptronics 2 board.

If +50 V voltage is absent on any fuse on the Fliptronics 2 board, then check fuse F112.  If that is good, and the other solenoids have power, either you have a connection problem, or the bridge is open (unlikely).

If voltage is present on one side of a fuse, but not the other, the fuse is blown.  Replace it and hope it does not blow again.

If the fuse blows again, did a flipper activate before the fuse blew?  If yes, you have a shorted TIP 102 or TIP36C.   If no, then the flipper coil is likely bad (shorted). Or, the diode on the flipper coil is shorted.  Or (unlikely) the diode for that coil (D17 through D24) on the Fliptronics 2 board is shorted.

If all the voltages check out, but a flipper or all of them do not work, you have a problem with the control side of this board.  That could be:

* The 50 V is not getting to the flipper coils.  Check the voltage at the coils.
* Ribbon cable to the Fliptronics board / CPU.  Either side.
* U2 (74HCT374) on the Fliptronics board is bad.
* Flipper switches or flipper opto switches are bad or not connected properly.

+12, +5 and ground 

If these are missing and they are good on the Power Driver Board, then you have a connector (plug, wire, header pin) problem.

Fliptronics Board (WPC95)

WPC 95 50V flipper power
WPC 95 50V Power

WPC95 uses the same technology as used in the Fliptronics 2 board, except that it is built into the Power Driver Board.  

What can go wrong

Not much.  The flipper power goes to the coils from J119 and this power is generated from the same power that runs the other high power 50 V DC solenoids.  If you tested TP 105 on the Power Driver Board and it is good, then the power to the flippers should be good. 

Voltage Tests

Set  your DVM to V DC.  Test TP 105.  If 50 V is present, then the coils should have power. 

Connect the black lead to any ground.  Touch the red lead to each side, one at a time to fuse clips F115 – F118.   Both sides of each fuse will likely read higher than the 50 V, because there is not a load.  70 V DC is common.

Troubleshooting

If no voltage is present on any fuse, then check fuse F107 & 108.  Those will blow if one of the diodes in the power supply is shorted.

If voltage is present on one side of a fuses F115 – F118, but not the other, the fuse is blown.  Replace it and hope it does not blow again.

If the fuse blows again, did a flipper activate before the fuse blew?  If yes, you have a shorted TIP 102 or TIP36C.   If no, then the flipper coil is likely bad.

If all the voltages check out, but a flipper or all of them do not work, you have a problem with the control side of this board.  That could be:

* Ribbon cable to the Power Driver board / CPU, J211 to J102.  Either side.  But that would affect a lot of solenoids.
* U5 (74HCT244) is bad.
* Flipper switches or flipper opto switches are bad or not connected properly.
* Power is not getting to the flipper coils.

Audio Board – Sound board

WPC89 and WPC-S have a separate audio board.  WPC95 combines the audio board with the video.  This applies to the audio board only.

WPC89 had two generations of sound boards: original and DCS.

What can go wrong

The WPC 89 sound board uses the + 5 V DC from the Power Driver Board.  But they also generate +12 V DC and -12 V DC from AC supplied to the board.  It is this power supply that can be the cause of failure.  The 1 uF Tantalum capacitors have a bad habit of failing, sometimes by vaporizing.   Inspect the board for signs of a failed small capacitor.

WPC89 DCS and WPC95 sound boards (Audio Video Boards) generate their own +5 and -5 V DC.

Voltage Tests

Set  your DVM to V DC.   If possible, connect your black ground probe to a ground on the board (see the above schematics.

WPC89 pre-DCS Sound Board
WPC89 pre-DCS Sound Board

WPC89 (pre-DCS)   Ground are pins 6 & 7 on J501 and pin 2 of J503.  The (+) side of C24 is also ground, but getting to that is tough.  The corner screws and the pad around them are also ground.

There are not any test points, but the easiest way to check the voltages are at the pins of J503.

J503 Pins (V DC)

1 = +5 from the Power Driver Board
2 = Ground
3 = -12 V
4 = +12 V

Troubleshooting

If the +12 or -12 are missing, then it is usually the failure of the voltage regulators LM7812 (+12) or LM7912 (-12) or one of the small Tantalum caps.   Less likely is a failure of one of the discrete power supply diodes. C24 or C25 can fail or leak.  Inspect those caps for leaks or bulges.  Also check fuses F501 & F502.  Failure of the fuses can mean a shorted diode or shorted / failed capacitor.

WPC89 DCS

WPC 89 DCS Sound Board
WPC89 DCS Sound Board

WPC89 DCS has a similar power supply except that it generates +5 and -5 VDC.

Ground are pins 6 & 7 on J4 and pins 4 & 5 of J3.  The corner screws and the pad around them are also ground.

There are not any test points and it is difficult to test the +5 and -5 DC.  U25 pin 1 has +5.  U26 pin 3 has -5.  It might be easier to connect to the (+) end of Tantalum cap C18 which has +5.  C19 on the (-) end is -5.

Troubleshooting

If the +5 or -5 are missing, then it is usually the failure of the voltage regulators LM7805 (+5) or LM7905 (-5) or one of the small Tantalum caps.   Less likely is a failure of one of the discrete power supply diodes. C20 or C21 can fail or leak.  Inspect those caps for leaks or bulges.  Also check fuses F501 & F502.  Failure of the fuses can mean a shorted diode or shorted / failed capacitor.

WPC95 Audio Visual Board (Audio only)

WPC95 has a similar power supply that generates +5 and -5 VDC.

Ground are pins 5 & 6 on J605 and pins 3 & 4 of J505 and J504.  The corner screws and the pad around them are also ground.

There are not any test points and it is difficult to test the +5 and -5 DC.  U7 pin 1 has +5.  U8 pin 3 has -5.  It is also possible to check for these voltages on several of the ICs.  U5 and U6 have +5 on pin 5, and -5 on pin 3.

Troubleshooting

If the +5 or -5 are missing, then it is usually the failure of the voltage regulators LM7805 (+5) or LM7905.   Less likely is a failure of one of the discrete power supply diodes. C36 or C37 can fail or leak.  Inspect those caps for leaks or bulges.  Also check fuses F501 & F502.  Failure of the fuses can mean a shorted diode or shorted / failed capacitor.