Williams WPC


Note: This page is a work in progress. Please help get it to a completed state by adding any useful information to it.

1 Introduction

This guide covers Williams WPC, WPC-S, and WPC-95 games.

2 Game List

2.1 WPC (Alphanumeric)

2.2 WPC (Dot Matrix)

2.3 WPC Fliptronics I & II

2.4 WPC DCS Sound

2.5 WPC-S CPU

2.6 WPC-95 CPU

3 Technical Info

Motorola 68B09E, running at 2Mhz. It is an 8-bit/16-bit CPU with a 64KB address space. Bank switching is required to address more than 64KB. The game ROM size varies from 128KB to 1MB, depending on the game. 8KB of battery backed RAM is available.

For more information, see The FreeWPC Manual

3.1 The WPC Transformer

3.2 The WPC System Boardset and History

3.3 WPC CPU Generations

3.3.1 WPC CPU

3.3.2 WPC-S CPU

3.3.3 WPC-95 CPU

3.4 WPC Power/Driver Board Generations

3.4.1 WPC-089 Power/Driver Board

3.4.2 WPC-95 Power/Driver Board

3.5 WPC Dot Matrix Controller board

3.6 WPC Sound Boards

3.6.1 WPC pre-DCS Sound Board

3.6.2 WPC DCS Sound Board

3.6.3 WPC-95 AV Board

3.7 WPC Fliptronics Boards

3.7.1 WPC Fliptronics I board

3.7.2 WPC Fliptronics II board

3.8 Miscellaneous WPC Boards

Note: Some of these might best be located in the "Game Specific Problems & Fixes" section. Perhaps the pervasiveness of their use within the WPC game list would drive the decision.

3.8.1 WPC 7 Opto Board

3.8.2 WPC 10 Opto Board

3.8.3 WPC 16 Opto Board

3.8.4 Auxiliary 8-Driver Board

3.8.5 Trough opto boards

3.8.6 WH2O & CFTBL chaser lamp boards

3.8.7 HSII & CFTBL triac board

3.8.8 Coin Door Interface Board

If your coin door interface board gets dusty from flipper parts wearing, clean it. That dust conducts electricity and will give you some interesting coinage issues.

4 Problems and Solutions

4.1 MPU boot issues

4.1.1 Relocating the battery from the MPU board

Relocating the 3xAA battery pack from the MPU board is always a good idea. Leaky alkaline batteries are the #1 killer of MPU boards. Simply removing the batteries is not an option with WPC games as you will always receive a "Factory Settings Restored" message when the game boots.

Options:

Remotely locate the battery holder somewhere below all other boards. This ensures that even if the remotely located batteries leak, they won't leak onto (or even drip onto) any circuit board. Replace the batteries annually, dating them with a Sharpie! as you do.
Replace the 6264 static RAM with a SIMTEK non-volatile RAM (STK12C68). These SIMTEK RAM chips are increasingly hard to find but offer a nice alternative to changing batteries annually. This method requires desoldering/soldering on the MPU and also has the down-side of not maintaining the Real Time Clock (meaningless in some games...nice in games like Twilight Zone that moves the playfield "toy" clock to the current time during attract mode, and Who?Dunnit which has a "Midnight Madness" feature).

4.1.2 Repairing Alkaline Corrosion

4.2 Game resets

4.2.1 A disciplined process to eliminate WPC game resets

One of the more annoying faults exhibited by WPC machines is the chronic reset problem. The game will restart - usually during a particularly exciting game, sometimes when both flippers are used at the same time.

There are several possible reasons for game resets. Before doing any work on the circuit boards, it is recommended that a number of much easier to fix, and just as probable root causes, be examined.

Possible causes are listed below, in the recommended order of examination. This order is a derived from a combination of "ease of examination" crossed with "probability of root cause".

5 WPC 5VDC Power Derivation Path

Following is the nominal path from the wall plug to eventual consumers of the clean 5VDC power supplied by the Power/Driver board.

120VAC/60Hz power is nominally provided at the wall plug. Different voltages are accommodated also (see below)
An RFI (radio frequency interference) filter, which is seldom a contributor to game problems.
Line power is connected to a service outlet sometimes incorporated into the metal "power box" and made available to the tech via a short, uniquely plugged, extension cord. Line power is wired in parallel and does not require the power switch to be in the ON position.
Both sides of the AC power pass through the double pole/double throw (DPDT) game power switch
The "black" side of the AC power passes through an 8A FB fuse housed in a bayonet style (screw in) fuse enclosure.
The "black" side of the AC power then passes through the thermistor, which limits current inrush into the system.
"Butterfly" voltage select connector used to accommodate typical voltage systems used around the world (120VAC in US, 230VAC abroad, low line voltage, etc). When configured for 120VAC in the US, the connector and wiring resemble a butterfly.
Transformer Primary windings
Transformer Secondary windings
Yet another Molex connector, mating with the harness that will eventually lead to the Power/Driver board.
Some games incorporate a "coin door interlock switch" which interrupts coil and flasher power when the coin door is open. If your game is equipped with this switch, there will be an extra molex connector necessary to implement this switch.
J101 on the Power/Driver board
Full Wave AC rectification and smoothing via BR2 and C5
Regulation to 5VDC via the LM323K at Q1
Lighting LED4...
And finally, delivery to 5VDC power consumers via J114, J116, J117, and J118

6 Low Line Voltage

Step 1: measure line voltage

Low line voltage can occur at three locations:

House entry
Withing home circuitry
Between the wall socket and the machine.

House entry: in midsummer when everybody is running air conditioning, the line voltage can drop. Pinball machines should tolerate this drop.

Inside the house: when your AC is running, it might cause a voltage drop that affects your machine.

From the wall: a common problem with power strips and several machines turned on.

If your machine is resetting, open the coin door and measure the AC voltage at the auxiliary socket with the machine turned off, and with the machine turned on. If the voltage is over 105V, you likely have a problem inside the machine. Below 105V - you need to fix your wiring.

7 Missing diodes, open diodes, or cold solder joints at the Flipper coils

Step 2: Examine flipper coil diodes

WPC flippers are, in general, the only coils in the game that should have diodes across the coil lugs. While diodes seldom fail, sometimes the pounding environment that flipper diodes must live within causes solder joints to fail. Ensure that each flipper coil has the required two diodes, that the diodes are good, and that they are soldered to the coil lugs with a quality solder joint.

8 Poor Connections between the Transformer Secondary and the Power/Driver Board

Step 3: Examine the "cube shaped" molex connector in the cabinet

The connections from the transformer secondary to the Power/Driver board can degrade over time, a natural result of hours and hours of "power on" time. Try re-seating each connector. If the reset frequency is reduced or disappears, then you've probably discovered the root cause. You should re-pin these connectors with at least new pins (the connector housings may be salvageable) for a long term solution.

Note: the molex pin extractor for these "round" pins is relatively expensive but there is no other good way to remove them.

9 Poor Connections between the Power/Driver board, the CPU, and other PCBs

Step 4: Examine other wiring harnesses and the connectors

Measure DC voltage at TP2 on the Power/Driver board.

DMM set to DC volts (if not an auto-ranging meter, expect to measure 5VDC)
Black lead secured to game ground (the ground braid in the head is a good place to pick up ground)
Red lead on TP2. Remember the reading

Measure DC voltage at the CPU board.

Again, DMM set to DC volts
Black lead in the same place
Red lead on pin 32 of the game ROM, or on pin 2 (center pin) of the MC34064 under voltage watchdog at U10
Record this reading

Compare the two readings. ANY difference indicates voltage loss across the connectors. Some voltage loss is expected/natural since no circuit path can provide zero resistance. A difference of .1VDC is enough to warrant examination of the connectors between J114 on the Power/Driver board and J210 on the CPU board.

Reseating the wire harness that connects the power-driver board to the CPU board may identify the root cause (but reseating is not a long term solution). Some games use an interceptor harness to power extra boards (IJ, TZ, WH20, etc). There is a inline splice connector (commonly called a Z-connector) between the driver board and the CPU board. You can replace the Z-connector or, more robustly, eliminate it by splicing the wires together, soldering and heat-shrinking. This removes the Z-connector as a contributor to game resets entirely.

Tarnished or heat damaged header pins create resistance and are sometimes a contributor to game resets. You can bet that if the male header pins are tarnished, their female mates are tarnished also. Should you find tarnished pins, now might be a good time to remove that aspect as a contributor to game resets.

If you are following this step-by-step process, now is the first time that you'll need to use a soldering/desoldering station.

Replace the male header pins, remembering to clip the correct "key" pin before reinstalling the board into the game.

Replace the female connector and pins with good quality Trifurcon crimp-on pins. IDC (Insulation Displacement Connectors) connectors as found originally on your game were used by the OEM to speed the manufacturing process and do not provide the level of robustness that can be achieved using Trifurcon crimp-on pins and good technique.

Another possible contributor to poor power connections is cracked header pin solder joints. Although, with WPC double-sided PCBs and the relatively large header pin through-holes, this is rarely seen. Should you identify cracked header pin solder joints, it's best to remove as much of the old solder as possible before reflowing new solder at the joint.

10 Using a Multimeter to Test the Bridge Rectifier and Capacitors

There's one last test we can do before disassembling parts of the machine. This test can clearly identify a bad bridge rectifier or capacitor. You will need a clip lead. With the machine off, clip the lead onto the top left lead (positive) of BR2. You will have to do this by feel, as you cannot see the lead. This clip point is the output of the bridge rectifier, and is connected to the capacitor and LM323K regulatr input. It should be at 9V DC.

Then, place the other clip on the red (+) lead of your meter, and connect the black lead to ground by tucking it under the braid. Check your installation to make sure that nothing is shorting.

Now, set your meter to DC volts and turn on the machine.

The meter should read 9V. This will be true with good and bad capacitors. If the bridge rectiifer is bad, it will read about 7V.

For the capacitor, turn your meter to AC volts. Note that inexpensive meters may give false readings here. Ideally, your meter should be a true RMS meter.

Good capacitors will read about 300mV AC. Bad capacitors will read up to 2VAC. Anything over 1V should be changed.

11 Failed Thermistor

Step 5: Examine the Thermistor

The thermistor is (generally) a black disk, about the size of a dime. If your game has one (and not all WPC games do), it will be connected in series with incoming AC power. It is located inside the power box which is found just inside the coin door and to the right. Note that the power box may also contain a "varistor", which is essentially a surge protector. The varistor will be wired in parallel with the AC power. The varistor is not a factor in game resets.

The thermistor's job is to limit current inrush into the capacitors when the game is first powered on. This reduces stress on the bridge rectifiers or diodes in the game's power circuits (which is the primary cause of bridge rectifier failures). After a few seconds, the thermistor heats up and drops to a very low resistance. Failing thermistors pass less current and have to get hotter to work. This heating takes time, so the game will often reset in the first 30 minutes of operation, and then be fine aftwerwards. Obviously, a cold environment will make the symptoms worse, and a warm room may appear to cure the problem.

Resetting while the game warms up is therefore a key indicator of a failing thermistor. Note also that DCS and AV boards may reset without resetting the game, causing the sound to jump to "LOUD".

***Safety Warning*** Unplug the game AND turn the game off before conducting the following test.

Sometimes, the thermistor may be visibly damaged. However, it may look good and still be bad. An easy test of the thermistor is to jumper across the legs of the thermistor with a heavy gauge wire. If the game resets no longer occur, replace the thermistor with the correctly rated part. The original Williams part number is 5016-12978-00. A replacement is available from Great Plains Electronics.

12 Questionable Prior Rework

Step 6: Examine prior rework

The printed circuit boards used in pinball machines sometimes have traces on both sides of the board. Most WPC boards are manufactured in this way. The traces are joined through the board by a thin layer of copper, plated to the inside of the hole. This plating is delicate. Without great care, the plating can pull out or crack when components are removed, especially alkaline damaged components as found on MPU boards (after batteries have leaked) and "snap caps" as found on OEM WPC Power/Driver boards (at C5 for instance).

Be careful when removing these components as it is very easy to lift traces or damage through-holes on the board. If the component is known to be bad, it is sometimes easier to snip the component from the board with a flush cutter and remove each leg of the component individually.

An excellent way to repair a lifted trace or cracked through-hole is to create a 'solder stitch' between the traces on each side of a two sided board. Some repairers will use jumpers to repair cracked through-holes or to "guarantee" connectivity between components. Some PCB repairmen will avoid the use of jumpers in favor of better looking rework. Others favor functionality over look.

13 Failed Capacitors

Step 7: Power smoothing capacitors at end of life

Electrolytic capacitors do not last forever. They are designed to operate for only 1,000 hours at their full rating. Capacitor life is a function of temperature: the cooler the capacitor operates, the longer the life. The system designer must select higher voltage and capacitance ratings to achieve the design life, which can be as short as 5 years in a pinball machine operated continuously in a warm environmemt.

The WPC Power/Driver board uses a 15,000uf, 25V capacitor to smooth the full wave rectified AC from BR2. When this capacitor is no longer smoothing the rectified AC well enough to produce a clean 5VDC, the voltage may drop below the threshold enforced by the watchdog circuit on the MPU (an MC34064 at U10). When this happens, resets sometimes result.

Note that commonly available replacement capacitors are rated to 35V, and will work fine for this application. In general, you may use a capacitor rated for higher operating voltages but in general, the spec capacitance (uf) should not be changed.

C4 (spec'd at 100uf, 10V) can sometimes fail and cause the game to reset also.

14 Failed Bridge Rectifier

Step 8: Test Bridge Rectifier #2 (BR2)

The thermistor protects the bridge rectifiers from inrush current. Still, bridge rectifiers will occasionally fail.

Testing a bridge rectifier is simple.

Place your DMM into "diode test".
Put the black lead of your DMM on the "oddball" lead of the bridge rectifier. This will be the lead that isn't oriented the same as the others (as with the "spade" type of bridge) or the lead that prevents the four legs from forming a square (as with the "wire lead" type of bridge). This will also be the DC positive lead of the bridge.
Place the red lead of the DMM on each of the adjacent legs, one at a time.
A reading nominally between .5 and .7 should be seen (this represents the voltage drop across the bridge's internal diodes).
Now place the red lead of the DMM on the lead opposite of the "oddball" lead, or the DC negative lead of the bridge.
Place the black lead of the DMM on each of the adjacent legs, one at a time.
Again, a nominal reading between .5 and .7 should be seen.

Readings outside of these ranges indicate a failed or failing bridge. Note that these readings are not "hard and fast". For instance, a reading of .452 is probably acceptable. We are looking for an "open" or a "short". Note also that this test is not conducted "under load" and it is possible for the bridge to test "good" when it will in fact fail under load (this is also true when testing diodes, transistors, etc).

Should you decide to replace the bridge, it is best to screw the heat sink to the bridge before soldering it in place as the heat sink is shared between BR1 and BR2. A small amount of heat sink compound between the bridge and the heat sink is necessary. This compound improves conduction of the heat away from the bridge and into the sink.

Some repair tips suggested cutting the bridge in half, separating it into two parts, one part for each bridge. This technique is no longer considered to be a best practice.

Solder both the top and bottom solder pads of the bridge. Should the through-hole of the bridge leads be cracked or otherwise damaged, use the "solder stitch" technique noted above or install jumper wires between the DC outputs of the bridge and the terminals of C5. When clipping the leads of the wire bridge, do not cut into the solder "meniscus" (the "volcano" of solder around the wire lead). Cutting into the solder meniscus can cause cracked solder joints later.

With proper desoldering tools, like the Hakko 808 or Hakko 470D, removal of bridge rectifiers and other components is greatly simplified.

15 Failed Voltage Regulator

Step 9: When all else fails...

The LM323K 5V regulator is a robust device, but it can drift over time to below the design requirement of 4.8VDC. If your 5VDC reads less than 4.8VDC at the test point, or less than 4.75V on the CPU board, you have to replace the regulator. Note that these voltages are compliant to the LM323K's spec. However, at the lower end of this spec, this lower voltage may be the cause of resets.

There is a method of absolute last resort. This is absolutely, positively a hack. And yes, it can push some extra margin into the design, covering up other problems, which is why it is a hack. But if you don't have the skills to uncover the real problem, here is what you can do.

The LM323K draws a small current to operate, which it passes to ground. We can use that current to raise the voltage of the whole LM323K, pushing the output closer to 5V.

Procedure:

Isolate the LM323K's metal case from board ground by cutting the ground traces that run left and right from the nut on the back of the board that bolts the LM323K to the board. The neater you make these cuts, the easier it is for someone else to later restore the board.
Some versions of the Power/Driver board include a ground trace on the component side of the board that provides a ground to tantalum capacitor C9. This trace must be cut on the component side of the board.
Add a 1/2W resistor in series, from the LM323K ground to the board's ground trace.

A 12 ohm resistor will nominally raise the LM323K voltage output by .1 VDC.
A 24 ohm resistor will nominally raise the LM323K voltage output by .2 VDC.
Note: The LM323K is designed to operate this way.

16 The Conductive Grease Hack

What is a "Hack"? Some techs will recommend the use of conductive grease to improve conductivity at a connector. While some techs will "swear by the stuff", other techs will "swear at the stuff", and as such, this is not considered a best practice. The grease can extend the life of new header pins, and protect against hostile environments that would cause corrosion. However, when used on header pins that are already damaged, grease can only slow further deterioration. Worse, the heat in the connector will turn the grease to gunk. If you find a flaky connector with gunk in it, you've been "greased" and you will want to re-pin it.

16.1 Check fuses F114 and F115 message

This message is sometimes displayed when the game boots and a game cannot be started. Most of the time, F114/F115 will be found to be just fine.

The game issues this message because it cannot read the switch matrix normally. The crafty designers at Williams inserted an “always closed“ switch into the matrix as switch 24. Switch 24 isn’t a switch at all, but instead provides the game software with a “known closed” switch matrix return. Switch 24 is actually a diode across column 2, row 4 of the switch matrix and is located on the coin door interface board.

Since the WPC switch matrix circuitry on the MPU uses 12V to determine switch state, the game assumes that the 12VDC power has been interrupted. F114/F115 fuse the 12V generation circuit; F114 on the AC side of BR1; F115 on the DC side of BR1. Hence, the game assumes that one of these fuses is blown and the message is displayed.

Diagnosing the problem

Start by checking DC voltage at TP3. You should see about 12VDC. If not, follow these steps.

Actually check fuses F114 and F115 using the procedure here. If a blown fuse is found, replace it. If F114 immediately blows again, then BR1 is probably shorted. Skip to the paragraph below to test the bridge.
Check LED6. If not lit (indicating the absence of 18V at TP8), then suspect BR1 or the filter caps for BR1, C6 and C7. If BR1 had failed shorted or if C6 or C7 where shorted (rare) then you would expect to see F114 blown. BR1 can be tested using the procedure below.
Check LED1. If not lit (indicating the absence of “digital” 12V at TP3, then test D1 and D2 (both 1N4004 diodes). If D1/D2 test good, then check continuity from pin 2 of the 7812 voltage regulator at Q2 to J114, pin 1. This verifies the path through F115.
If this all checks out, yet 12VDC is still not at TP3, then suspect the 7812 voltage regulator at Q2. Q2 is in a TO-220 package (like a TIP-102) and has a small heat sink attached.

If TP3 does, in fact, have 12VDC present, then we need to dig deeper.

First check for 12VDC on the CPU board to ensure that the 12V is getting to the board via the 2 (and possibly 4 if your game has a “Z-Connector”) connectors that carry the 12VDC. An easy place to measure 12VDC on the CPU is at pin 10 of the ULN2803 (U20). Pin 10 is on the bottom row of pins, furthest left. Note that this connection (an also the 12VDC connection to pin 3 of the LM339s) is not shown on the schematic.
If the CPU is receiving 12VDC, and you still have the “Check fuses F114 and F115” message, then the problem lies within the CPUs switch matrix logic circuitry.
Prime candidates for CPU switch matrix failure are U20 (a ULN2803), the two LM339s at U18 and U19, the 74LS374 at U14, and the 74LS240 at U13. All of these ICs are in the “corrosion zone” caused by leaky alkaline batteries. If your CPU exhibits the “blue/green fuzzies”, address the alkaline damage first.
Testing the 74LSXXX ICs is simple using the procedure here.
If coil power, flasher power, or even lamp power was somehow shorted to the switch matrix, there is a near 100% probability that the ULN2803 at U20 has been damaged. There is no good way to test the ULN2803 other than using a logic probe with the game powered on. Both the input side and the output side of the ULN2803 should be toggling between logic 0 and logic 1. If not, socket and replace the ULN2803.

File:Test-br.jpg

Checking an uninstalled bridge rectifier

Testing a bridge rectifier is simple.

Place your DMM into "diode test".
Put the black lead of your DMM on the "oddball" lead of the bridge rectifier. This will be the lead that isn't oriented the same as the others (as with the "spade" type of bridge) or the lead that prevents the four legs from forming a square (as with the "wire lead" type of bridge). This will also be the DC positive lead of the bridge.
Place the red lead of the DMM on each of the adjacent legs, one at a time.
A reading nominally between .5 and .7 should be seen (this represents the voltage drop across the bridge's internal diodes).
Now place the red lead of the DMM on the lead opposite of the "oddball" lead, or the DC negative lead of the bridge.
Place the black lead of the DMM on each of the adjacent legs, one at a time.
Again, a nominal reading between .5 and .7 should be seen.

Readings outside of these ranges indicate a failed or failing bridge. Note that these readings are not "hard and fast". For instance, a reading of .462 is probably acceptable. We are looking for an "open" or a "short". Note also that this test is not conducted "under load" and it is possible for the bridge to test "good" when it will in fact fail under load (this is also true when testing diodes, transistors, etc).

The heat sink covering BR1 and BR2 on a WPC-board

Take special care when replacing a bridge rectifier. It is easy to lift the traces of the plated through holes when removing these. After removing the heat sink, cut the old bridge rectifier off of the board close to the top leaving as much of the lug as possible. Then add a small amount of solder to the connection on the solder side to improve heat transfer. Finally apply the iron to the solder side to heat the joint and remove the remaining lug with small pliers.

When replacing the new bridge rectifier you should remove the old thermal compound and apply a new thin layer. The old compound can be removed with a little rubbing alcohol. Apply the thermal compound to the top of the bridge rectifiers and reattach the heat sink with the screws. It is much easier to replace the heat sink before resoldering the new bridge rectifier. Make sure that the heatsink is sitting flush with the tops of the bridge rectifiers and that you leave about a 5/8" gap between the bridge rectifier and the board to improve air flow.

Splitting the heat sink between BR1 and BR2 was at one time thought to improve reliability. This is no longer considered a best practice and is not recommended.

More info about replacing bridge rectifiers can be found in the section regarding system resets.

Diodes replaced BR1 and BR2 on WPC-95 boards

In WPC-95 games, BR1 and BR2 were replaced by a series of diodes. D11-D14 replaced BR1. D7-D10 replaced BR2. These are much less prone to failure. Still, they do fail on occasion. If they fail, it's best to replace all four in the "gang".

16.2 Voltage Problems - LED2 & LED3

LED2 and LED3 on the Power Driver Board are indicators for the line voltage detection circuit. On on-board comparator circuit uses +5V and +18V to check the line voltage. The comparator consists of a resistor voltage divider and an LM339 comparator.

The following table shows how to interpret the LED states. Note that other problems with the +18V or +5V supply could cause a high or low line voltage indication.

Line Voltage Indicator Chart

LED2	LED3	Voltage
On	Off	OK
Off	Off	High
On	On	Low

16.3 Solenoid & Flasher problems

Before proceeding to diagnose solenoid or flasher problems, see this section: How coils and flashers are turned on

16.4 Lamp problems

Lamps (or globes for those of you in the UK) fall into two categories. "General Illumination" and "Controlled Lamps". Your game probably has other lamps which are actually "flashers" that require an 89 or 906 bulb. Flashers are covered elsewhere in this Wiki.

General illumination lamps (GI) provide the ambient lighting for the playfield, backbox, and coin door. These lamps are list most of the time. The only "controllable" aspect of these lamps is their brightness.

Controlled lamps are under complete CPU control via the lamp matrix. These lamps illuminate the various "features" of the game such as mode inserts, pop bumper lamps, inlane/outlane insert lamps, etc.

16.4.1 General Illumination Problems

Background

The WPC power/driver board provides 5 GI circuits under CPU "brightness control". The WPC-95 power/driver board provides 3 GI circuits under CPU "brightness" control and 2 circuits that are always powered. Those two circuits are always connected to the backbox lamps.

GI power is provided by the transformer in the form of 6.3VAC at power/driver board connector J115. Although there are five pairs of wires, they are all connected together at the transformer. One side of the AC GI circuit on the power/driver board is fused by F106 through F110 which are all 5ASB fuses. This side runs to the GI lamps, and carries 6.3VAC to the backbox, playfield, and coin door via power driver board connectors J120, J121, and J119 respectively. J119 is a 3-pin header that is always connected to the coin door lamps. J120 and J121 are electrically and physically identical (keyed at pin 4) and therefore can be connected to either the female playfield GI connector or the female backbox GI connector without care. The other side of the GI AC feed is connected to ground.

The GI power is controlled by a triac in the return line from the playfield. When these triacs are off, no current passes and the lamps are off. When the triac is turned on, the GI lamps glow. The triac is a slightly special part - it must be a "four sector" triac. This means that it can switch both positive and negative sides of the AC cycle with only a positive signal.

Each triac is switched on/off by a 2N5401 transistor which is controlled by U1, a 74LS374, an octal D-Type Flip-Flop with three state outputs (a fancy way of saying that the device is an 8-bit data buffer).

The CPU can dim the GI by switching on the GI for only parts of the AC waveform. To do this, it uses a zero crossing signal generated from the 6.5VAC that feeds the 5V circuit.

Wire colors to J115 during the early WPC games were always yellow (AC) and yellow-white (AC return). Pin 1 of J115 provides the "ground reference". Later WPC games used different wire colors at J115 and instead of "looping" power through the connector at J115, connected two wires to the same pin at the 9-pin connector between the transformer secondary and J115.

J119 is always keyed at pin2, with a white-Violet wire at pin 1 and a Violet wire at pin 3

J120 and J121 are 11 pin connectors. Wire color/positions (when used) are identical for all WPC games and are shown in the table.

Pin	Wire color at J120/J121
1	Brown
2	Orange
3	Yellow (yellow)
4	Key
5	Green
6	Violet
7	White-Brown
8	White-Orange
9	White-Yellow (yellow)
10	White-Green
11	White-Violet

Common GI Problem Causes (listed by probability/ease of testing and correction)

GI Bulbs Not Lighting

Let's start by determining if the problem is "off board", i.e. not on your power/driver board, or "on board".

Take note of the wire color of the GI string that is not working.
Set your DMM to AC voltage. If your DMM is not an "auto-ranging" model, expect to measure about 7 volts AC.
Turn the game on.
Insert one probe of your DMM (either one) into the rear of the female connector position with the same wire color as noted earlier. Make sure you make contact with the conductor.
Insert the other probe into the rear of the female connector with the white wire that has the same color "tracer" as the color noted earlier.
You should be measuring 6 to 7 VAC.
If there is voltage at the connector, then the problem is "off board".
If there is no voltage at the connector, then the problem is "on board".

Off board GI problems

All lamps blown. Don't laugh. Just for giggles, put a known working lamp into one of the lamp sockets of the suspected GI string. I've seen it more than once. Usually the result of operators never changing a bulb, or somehow connecting higher voltage to the circuit.
"Open" in GI wiring. The GI wires leading from J120/J121 may be cut/broken between the connector and the GI lamp sockets. Remove both of the female connectors at J120/J121. Use your DMM to check continuity between the lamp socket and the appropriate wire/pin at J120/J121.

On board GI problems

Blown fuses. This is also the easiest problem to fix. Check each GI fuse following this procedure. Don't trust your eyes.
Burned connectors. <need a picture> Over long periods of time, both the male and female GI connectors at J115, J120, and J121 often burn. This was especially prevalent in early WPC games like Terminator 2. Numerous "hacks" have been employed over the years by well meaning repairmen but the only real way to fix burned connectors is to replace both the male header pins and the female housings/pins. "Trifurcon" phosphor-bronze crimp-on pins are recommended to provide a better connection at the female connector. Note that these must be phosphor-bronze (7A rating, as original). Don't buy them unless the supplier calls that out as the brass version looks the same but is only rated at 5A. If you replace burned female connectors, the male connectors are probably burned too and should be replaced. The damaged surface of the male pins will generate heat, and cause early failure of the replacement connector. Plus, the GI will be dimmer than it should be. J115 is a special case. The black Panduit connector that Williams used on many machines is far superior to any crimp pin, with a 12A rating (compared to 7A for phosphor-bronze Trifurcon pins). These, however, can be hard to find. Fortunately, they rarely burn and therefore rarely require service.
Burned AC power input connector. There is also a 9-pin (3x3) connector between the transformer secondary and J115. This connector/pins sometimes burn and may require replacement. Check to ensure that AC power is being delivered to the power/driver board at J115.
1. Set your DMM to AC voltage. If your DMM is not an "auto-ranging" model, expect to measure about 7 volts AC.
2. Turn the game on.
3. Insert one probe of your DMM (either one) into the rear of the female connector at J115, pin 3.
4. Insert the other probe into the rear of the female connector at J115, pin 11.
5. You should be measuring 6 to 7 VAC.
6. If no voltage is present, examine the 9-pin connector between the transformer secondary and J115.
Burned traces. Usually, this is a secondary problem created after the connectors burn. Visual inspection of the traces might uncover the problem, but "buzzing" them for continuity is the best practice.
Failed 2N5401. These don't fail very often, but are easy to test following this procedure.
Failed resistors. Again, these don't fail very often but are easy to test with your DMM. Keep in mind that "in-circuit" measurements may not be reliable.
Failed 74LS374. This is rare too but easy to test following this procedure. You can also test the outputs of the LS374 by probing pins 2, 5, 6, 16 and 19 with your logic probe. At full GI brightness, these pins should test as "high".
Failed Triac. These rarely fail. But, if you've gotten to this step in the procedure, it's time to replace the Triac. Remember, you need a 4-sector triac.

As these boards age it is easy to pull out the little copper hole liners that connect traces from one side of the board to the other. If you install new connector pins, be sure to check continuity from the new pins onto the board somewhere. This only takes a couple minutes and can save you a lot of time.

GI Lamps Not Dimming

The primary cause of this problem is broken traces at BR2, usually caused when BR2 was replaced. These traces feed D3 and D38. Both of these traces must be intact for dimming to work.

16.4.2 Controlled Lamp Problems

Under construction...

16.5 Switch Problems

Switches in WPC games fall into two categories, those within the switch matrix, and "direct" switches.

16.5.1 Direct Switch Problems

Direct switch operation

Direct switches include:

Left coin chute
Center coin chute
Right coin chute
4th coin chute
Service Credits/Escape (referred to as "escape" here)
Volume down/Down
Volume up/Up
Begin Test/Enter

Direct switches are not part of the WPC switch matrix. All of the direct switches are located on the coin door, and connect to the MPU at J205. The MPU senses these switches individually, and apart from the switch matrix. Therefore, isolation diodes are not used with direct switches.

Normally, with the switch open, the LM339s at U16 and U17 compare 12V (supplied on the MPU to both the switch and to the LM339) with 5V (as a comparison level) and signals the 74LS240 at U15 that the switch is open. When the switch closes, it shorts the 12V to ground and the comparison at the LM339 then indicates to U15 that the switch is closed. U15 is "clocked" by pin 48 of the ASIC (SW DIR), causing U15 to present its data to the data bus. The 6809/ASIC "debounces" the switch. Debouncing is not a factor to be considered here and doesn't factor in switch testing at all.

Direct Switch Pinout at J205 for both WPC and WPC-S MPUs
Notes:

J205, pin 5 is the "key" pin.

J205, pin 10 provides ground (black wire)

J205, pin 11 is unused

J205, pin 12 is an "enable" back to the coin door interface board

Signal	Wire color at J205	MPU pin	Diode	LM339 & input pin	U15 input pin
Left chute	orange/brown	J205-1	D15	U17-5	11
Center chute	orange/red	J205-2	D16	U17-7	13
Right chute	orange/black	J205-3	D17	U17-11	15
4th chute	orange/yellow	J205-4	D18	U17-9	17
Escape	orange/green	J205-6	D11	U16-9	2
Down	orange/blue	J205-7	D12	U16-11	4
Up	orange/violet	J205-8	D13	U16-7	6
Enter	orange/gray	J205-9	D14	U16-5	8

Debugging direct switch problems

To discover the problem as quickly as possible, we'll divide the problem into smaller pieces. We must first determine if the problem is on the MPU board or the problem lies with the wiring to the coin door and/or the specific switch. If your MPU has obvious alkaline damage at U15, U16, or U17, address the alkaline damage first.

Begin testing with the game OFF.

Isolate the problem to the MPU or to the game wiring/switch

Remove connector J205 from the MPU.
Build a jumper wire with alligator clips on both ends.
Clip one end of the jumper wire to the game's ground braid in the game head.
Turn the game on
Carefully touch the other end of your jumper wire to the appropriate pin on J205 as shown in the table.
If the MPU carries out the function of the switch, the problem is not on the MPU.
If the MPU does nothing, the problem is on the MPU.
Skip to the appropriate section below.

Identifying problems NOT on the MPU

Test the direct switch's path to ground

Your game should still be turned off.
DMM set to continuity.
Clip the black lead of your DMM to any game ground, like the lockdown bar or ground braid.
Red lead on the solder joint between the switch and the black wire that provides ground.
You should hear "tone". If not, further diagnose the break in the black wire between the solder joint and game ground.

Test the direct switch itself

Black lead of your DMM still clipped to game ground.
Red lead on the solder joint opposite the black wire (or bare wire jumper) of the switch under test.
Depress the switch. You should hear "tone". If not, the switch is defective and not "making". See the section below that describes cleaning these switches.

Test the signal path to the MPU

Clip the black lead of your DMM on the solder joint opposite the black wire (or bare wire jumper) for the switch under test.
Remove the connector plug at J205 from the MPU.
Red lead on the appropriate pin of J205 for the switch under test. See the table above. It's easiest to access the pin through the rectangular hole in the back of the connector where the pin's "tang" snaps in.
You should hear "tone". If not, there is a discontinuity in the wire between the direct switch and J205. Note that the coin door interface board is between these two points. The coin door interface board is a "pass-through" for these signals and rarely causes a problem. Still, reseating connectors J1, J3, and J4 on the coin door interface board might uncover the problem. More likely, the wire between J1 on the coin door interface board and J205 has a break in it.

Identifying problems on the MPU

Test the signal path through J205 and onto the MPU
J205 is right below the battery holder and as such, sometimes receives the unwanted gift of dripping alkaline from depleted batteries. Carefully examine both the male and female connections of J205 for alkaline "greenies". Assuming no alkaline damage...

Begin with your game turned off.
Connect J205 to the MPU.
Clip the black lead of your DMM to the solder joint opposite the black wire (or bare wire jumper) for the switch under test.
Red lead on the banded end of the appropriate diode shown in the table above.
You should hear "tone". If not, there is either a problem with the physical connection at J205 or the alkaline "greenies" are sneakier than you gave them credit for. Re-examine J205 and the surrounding area of the board for alkaline damage. The traces from the switch connectors are very small and it takes very little alkaline damage to compromise them. You may also re-pin the female side of J205.

At this point, a logic probe would be the best tool to use. You can pick up 5V power for your probe across the electrolytic cap at C31 which is immediately to the right of the battery holder. Black lead on the negative side (top of the cap). Red lead on positive side (bottom). The board is silkscreened with polarity markings. Set the logic probe to "CMOS" test mode, as you will be measuring 12VDC.

If you don't already have a logic probe, you should. Although for this test, you can still get by with your trusty DMM. Clip the black lead of your DMM to game ground. The ground braid in the head is a good place to pickup ground at this point. Set your DMM to DC volts.

Test the LM339 inputs

Start with the game turned off.
Again, set your logic probe to "CMOS"
Clip one end of your jumper wire to the appopriate pin of J205. Leave the other end of your jumper wire unconnected, but handy as you'll touch it to ground later.
You now need to turn the game ON.
Measure the signal at the appropriate LM339's appropriate pin shown in the table above. Either place your logic probe on the pin or place the Red lead of your DMM on the pin. The signal should measure high (or about 12VDC with your DMM).
Now, with your other hand, touch the free end of your jumper wire to the ground braid in the backbox as you observe the results.
You should see the signal transition to low. If you still measure high, then the pin isn't being grounded correctly. Candidates are a failed diode/resistor in the circuit, the board trace between the diode and the LM339 is compromised, or a badly failed LM339.

Test the LM339 outputs/74LS240 (U15) inputs

Set your logic probe back to TTL as you will be measuring 0 - 5V signals
Measure the signal at the appropriate pin (see table) of U15. The signal should measure high (or about 5VDC with your DMM).
Touch the free end of your jumper wire to the ground braid in the backbox as you observe the results.
You should see the signal transition to low. If you still measure high with the jumper wire grounded, then either the LM339 outputs have failed, the board trace between the LM339 and U15 is compromised, or the 74LS240 has failed and is corrupting the signal. You can test U15 using the procedure in the "How to..." section of PinWiki, here.

The output side of U15 can't be tested effectively since that is the processor/ASIC data bus and should be constantly and irregularly changing states.

If you've followed this process step-by-step, you should have identified the problem with the signal and will be able to effectively perform the appropriate repair.

Cleaning direct switches

Coming soon...will describe disassembly and cleaning... Sometimes, several rigorous open/close cycles will "clean" corrosion from the switch.

16.5.2 Switch Matrix Problems

Isolate the problem to the MPU or to the game wiring/diodes/switches

Follow these steps to determine if the switch matrix problem is on the CPU or somewhere in the game wiring.

Begin with the game turned off.
Remove connectors J206/J207, J208/209 and J212 from the bottom of the CPU (J206 and J207 are electronically the same and J208 and J209 are electronically the same).
Clip one lead of a test jumper to pin one of J207 making sure you don't touch any of the nearby pins on J207.
Clip the other lead to the banded end of a 1N4004 diode (a 1N4001 or similar diode will work as well). If you don't have a diode you can use just the jumper wire without a diode with the switch matrix connectors removed from the CPU.
Power the game on, and enter Switch Edge test (you've left J205 on the CPU so the diagnostics switches still work).
Touch the non-banded end of the diode to pin one on J209, then pin two and so on. You should see (and hear) the CPU indicate that switches #11, #12, #13, etc. are being "made" as you touch the pins of J209.
Move the jumper from J207 pin one to J207 pin 2 and repeat the J209 shorting. Do the same for the rest of the pins on J207 until you've tested all the pins of J207 and J209.

If only one switch shows on the Switch Edge test for each pin jump, then you've ruled out the CPU as the problem and you have a shorted wire or bad/broken/shorted diode on the playfield somewhere.

If multiple switch closures are reported when you touch one pin of the connector, or a row or column short is reported, then the problem lies within the switch matrix circuitry on the CPU.

16.6 Display problems

Under Construction

Display problems are usually the result of failing dot matrix displays themselves, flakey ribbon cables or connectors, ribbon cables installed "one row off" (or even one column off), failing high voltage sections of the dot matrix controller board, and rarely logic IC problems on the dot matrix controller board.

Pictures of failed or failing displays here would be nice.

Start by checking the easy things first.

Reseat the narrow ribbon cable between the DMD controller board and the DMD.
Reseat the wide ribbon cables from the MPU to the DMD controller.
Ensure each ribbon cable is correctly mated, and not "one row off".

Next, test the voltages supplied by the DMD controller to the DMD. Measure voltages at the DMD per the article "The WPC Dot Matrix Controller"

Bally/Williams and Data East have similarities with the 128x32 display. The display itself is interchangeable between manufacturers. DMDs do have a limited lifetime and will eventually outgas. Please see the information about outgassing displays in the Data East section.

16.7 Sound problems

16.7.1 Lowering the Minimum Volume

By default the game volume will go no lower than '8' to prevent an operator from setting the volume too low. This can be overridden by entering the adjustments menu and setting Adjustment 1.28 (Minimum Volume Override) to yes. You can now set the volume as low as you like.

16.7.2 Unbalanced Sound with pre-DCS sound boards

Pre-DCS sound boards are not 100% interchangeable across games. Games from Funhouse to Party Zone (including Funhouse, Harley Davidson, Bride of Pinbot, Slugfest, Gilligan's Island, Terminator 2, Hurricane, and Party Zone) use different resistor values at R23/R24 than the remaining games that used the pre-DCS sound board (games from Hot Shots basketball through The Addams Family Gold). If you find the sound "unbalanced" between background sounds and voices, for instance, check the following resistor values.

R23/R24 values for...

Funhouse through Party Zone - 150K ohms

Hot Shots through TAFG - 56K ohms

Note that the resistor value indicated in the schematics for pre-DCS sound boards at R22 and R25 are wrong. The schematics indicate 150K ohms. The correct value is 120K ohms.

16.7.3 Distorted or slightly "off" sounds

The pre-DCS sound uses the capacitors as filters in the sound circuit; C15, C36, and C38. If one or more of these caps fail, certain frequencies may not sound as loud or as clear. The game will just sound "off" with perhaps slightly imbalanced sounds.

16.7.4 Wrong sounds being played

Generally, this problem boils down to a communication problem between the MPU and the sound board. Possible failure points are:

Ribbon cables
Male header pins on both MPU and sound board
74LS374 data buffer ICs used to communicate between the MPU and the sound board.
Rarely, a failed 6264 RAM can cause this. The RAM is "tested" by the MPU. Sometimes it will pass the test, yet fail in game play. Odd...I know.

16.8 Flipper problems