Where Bally took the approach that the boot-up diagnostics were very important and game diagnostics were not, Williams took the opposite approach that boot-up diagnostics were *not* important but game diagnostics were! Hence where 1977-1985 Bally games don't really have a lamp, display, coil or switch test, Williams system3 to system7 games do have good versions of these tests (assuming that the game in question will boot up properly!)

System4 to System7 Diagnostics.
The diagnostic firmware is located in the "Flipper ROMs" at IC20 and IC17. Remember our previous discussion of this, system4 uses yellow flipper ROMs, system6 uses green flipper ROMs, and system7 uses blue flipper ROMs. System3 (white flipper ROMs) diagnostics are different to access, so see the section on that below. But the system4 to system7 diagnostics are pretty easy to use following these instructions. These diagnostics will test the score displays, the lamp matrix, the switch matrix (and on system7 a separate test for sound).

For system4 to system7 games, to use the internal game diagnostics, the game will need to boot up into attract mode. To access the switch diagnostics, there are a pair of switches inside the coin door that need to be accessed. Here are the steps used to access the diagnostics on system4 to system7 games:

• Turn the game on and allow it to go into attract mode.
• With the coin door open, press the coin door Auto-up/Manual switch into the manual position.
• Press the coin door Advance button. On system3 to system6, the score displays should go blank. On system7, all the score displays will light up with "0000000".
• Press the coin door Auto-up/Manual switch into the auto-up position.
• System3 to System6 only: Press the coin door Advance button.
• The game should now go into the first test, which is the SCORE DISPLAY test. All the score displays (including the credit/ball-in-play) should cycle from "000000" to "999999". If a particular display does not work or shows the wrong values, go to the score display repair section.
• System 7 only: Press the Advance button again to pass over the score display test. This will go to test 00, as indicated in the credit score display, which is the SOUND test. Each sound number will be displayed in the ball-in-play window, and played by the sound board. If a sound is missing or there is no sound, go to the sound repair section.
• Press the Advance button again to pass over the previous test. This will go to test 01, as indicated in the credit score display, which is the LAMP MATRIX test. All the CPU controlled lamps will cycle on and off at once. If a number of lamps are not working (and it's not burnt out bulbs), go to the lamp matrix repair section for more details.
• Press the Advance button again to pass over the lamp test. This will go to test 02, as indicated in the credit score display, which is the SOLENOID test, and each solenoid from 01 to 22 (as indicated in the ball-in-play display) will be exercised. Remember on system3 to system6, coils 9-13 are usually sound drivers. System7 games will also test coil numbers 23,24,25 (25 is the flipper relay, but 23/24 are unused in all system7 games). If a particular coil or group of coils does not work, go to the coil repair section. Note for the special solenoids (coils 17 to 22), be sure to test these solenoids using the playfield trigger switches too. Just because a special solenoids 17 to 22 work in diagnostics does *not* mean they work in the game, as these coils have two distinct hardware triggers.
• Press the Advance button again to pass over the solenoid test. This will go to test 03, as indicated in the credit score display, which is the SWITCH MATRIX test. On system3 to system6, the ball-in-play display will show the last read (closed) switch number. On system7 only, if there are multiple switches closed, the switch numbers will alternate in the ball-in-play display. If a switch or number of switches do not work, go to the switch matrix repair section.
• Press the Advance button again to pass over the switch matrix test. This will go to test 04, as indicated in the credit score display, which is the AUDITS. The ball-in-play display will show the audit number, and the player1 score display will show the audit value. The Advance button can be pressed to move from audit to audit. Check the game manual for a list of audit numbers and what they represent.

To exit the diagnostics or audits, turn the game off and back on. On system3 to system6 games, after accessing the last audit number, pressing Advance will wrap the audits back to audit number 01. On system7 games, after accessing the last audit number, pressing Advance will put the game back into attract mode.

System3 (White Flipper ROM) Diagnostics.
On system3 (white flipper ROM) games, getting to the diagnostics is a bit tricky (sometimes it will frustrate me so much, I end up putting yellow or green flipper ROMs and an appropriate Game ROM temporarily in the CPU board so I can easily get to the diagnostics!) Once you have done it a few times and understand the timing, it's a lot easier.

Having good batteries in the CPU board with system3 white flipper ROMs is also very helpful. No batteries and a system3 ROM CPU board acts strange (compared to system4 to system7 games), and is more difficult to get into diagnostics. With no batteries the game will boot into audit mode (often "01 04" or "18 04" on the score ball/credit display, and if the manual-down/auto-up switch is in the auto-up position, it will auto-increment the first number pair). Also white flipper ROM diagnostics run slower than yellow and newer flipper ROM diagnostics. You will notice this especially in the solenoid and switch test modes, as it seems the game is almost in slow motion in it's reactions, compared to later games.

Here are the system3 white flipper ROM diagnostic instructions:

1. With the game in attract (game over) mode, set the coin door Auto-up/Manual-down switch to Manual-down.
2. With the coin door open, press the Advance button once. This should show audit #18 in the credit display ("18 04" in the credit/match displays).
3. Press the Auto-up/Manual-down switch to Auto-Up. The audits will now start auto-incrementing, counting up, automatically showing the audits.
4. Press the Advance button twice, with about 1/2 second of time between the two button presses. Yea I know, this sounds very precise, but it must be done this way! This is where the "timing" comes in, and practice is the only real way to get this. If done correctly, the score displays should now be blank. If the two switch presses are done too fast or too slow, the game will return to attract mode, and you'll have to start over at step one above.
5. Press Advance once again, and the game should now go into the first test, which is the SCORE DISPLAY test. All the score displays (including the credit/ball-in-play) should cycle from "000000" to "999999". If a particular display does not work or shows the wrong values, go to the score display repair section.
6. Press the Advance button again to pass over the score display test. This will go to test 01, as indicated in the match (ball in play) display, which is the LAMP MATRIX test. All the CPU controlled lamps will cycle on and off at once. If a number of lamps are not working (and it's not burnt out bulbs), go to the lamp matrix repair section for more details.
7. Press the Advance button again to pass over the lamp test. This will go to test 02, as indicated in the match/ball in play display, which is the SOLENOID test, and each solenoid from 01 to 22 (as indicated in the credit display) will be exercised. Remember often system3 games coils 9-13 are sound drivers. If a particular coil or group of coils does not work, go to the coil repair section. Note for the special solenoids (coils 17 to 22), be sure to test these solenoids using the playfield trigger switches too. Just because a special solenoids 17 to 22 work in diagnostics does *not* mean they work in the game, as these coils have two distinct hardware triggers.
8. Press the Advance button again to pass over the solenoid test. This will go to test 03, as indicated in the match/ball in play display, which is the SWITCH MATRIX test. The credit display will show the last read (closed) switch. If there are multiple switches closed, the switch numbers will *not* alternate in the credit display. If a switch or number of switches do not work, go to the switch matrix repair section.
9. Press the Advance button again to pass over the switch matrix test. This will go to test 04, as indicated in the match/ball in play display, which is the AUDITS. The credit display will show the audit number, and the player1 score display will show the audit value. The Advance button can be pressed to move from audit to audit. Check the game manual for a list of audit numbers and what they represent.

To exit the diagnostics or audits, turn the game off and back on. On system3 to system6 games, after accessing the last audit number, pressing Advance will wrap the audits back to audit number 01.

Pulse Lengths in Diagnostics.
The length of time a coil is "pulsed" in diagnostics may not be long enough to make the device "dance". That is for example, in game mode, it takes a fairly long pulse to reset a drop target bank. But in diagnostics, usually shorter pulses are used. So if that drop target bank does not reset in diagnostic mode, don't worry about! Wait until game play and test the coil there before working on something that isn't really broken.

Random lock-ups and resets includes the game shutting down during play or attract mode, or it just goes crazy making random sounds and scoring invisible points. Another commonly seen reset is if both cabinet flipper buttons are pressed during game mode, the game ends and goes into "attract" mode. If the backglass is removed and this repeated, you will see the game is actually rebooting (note the LEDs flash or on system7 the "0" code flashed on the segmented LED). These problems are usually caused by either one of three problems: power supply ripple, weak bridge rectifier, connector failure, or a bad coil diode.

For example, if the game resets when pressing one or both flipper buttons, then there may be a broken or missing diode on a flipper coil. A broken diode allows the voltage to reverse back to the power supply. This is caused by the collapse of the coil's magnetic field (interestingly, a 30 volt coil will produce a 60 volt back "spike"). This completely freaks out the power supply, causing the game to reset. Replacing the coil's diode usually fixes this problem.

Game Resets.
If the game resets when pressing one or both flipper buttons, then there may be a broken or missing diode on a flipper coil. A "reset" is classified as this: If both cabinet flipper buttons are pressed during game mode, the game ends and goes into "attract" mode. If the backglass is removed and this repeated, you will see the game is actually rebooting (note the LEDs flash or on system7 the "0" code flashed on the segmented LED). Check the flipper coil diodes first as it's the easiest thing to check. Gently tug on the flipper coil's diode(s) to see if they are cracked or not properly soldered to the coil's lugs. If no problems are seen with the flipper diodes, next check the power supply filter capacitor for AC ripple. With the game on put the DMM leads across the power supply's large filter cap. Less than .200 volts AC should be seen on system7 (or system9/11), and less than .300 volts AC on system3-6. If more than that is seen, replace the filter cap. On System3-6 games with more than two flippers, use a 15,000 MFD filter cap. On system3-6 games with two flippers, a 10,000 MFD filter cap should work fine. On system7 (or system9/11) I recommend a 15,000 MFD filter cap.

Also on system7 (and system9 and system11) games, often the power supply's 5/12 volt bridge rectifier needs to be replaced. I install a new 35 amp 200 volt bridge rectifier. Replacing the bridge and the filter cap will usually fix a flipper-envolked reset problem.

Game Lock-Ups: a Summary of What Could be Wrong.
At this point, all the circuit board updates and modifications should have been performed. If the game boots, it is now time to test for random resets and lock ups. If a reset/lockup happens, it is usually related to the following:

1. Bad CPU/Driver 40 pin interboard connector.
2. Bad CPU/Driver board chip sockets ("Scanbe").
3. Bad board connectors and cracked solder header pin solder joints.
4. Bad 1J2 CPU board power connector.
5. Bad +5 volt filter capacitor.
6. Bad bridge rectifier (system7).
7. Missing/broken diodes on a coil(s).
8. Problem with the switch matrix.

The first thing to notice is if the problem occurs only during game play, or just while the game is in attract mode (in both circumstances). The second thing to notice is does the game reset, or does it lock up (a lock up is defined as the two CPU board LEDs are on, or there's a "0" on the 7-digit System7 CPU board display).

If the game *resets* during play, this is usually a power related problem (bad coil diode, bad +5 volt filter capacitor, or problem with the switch matrix). See above for solutions to that. If the game *locks-up* during play or in attract (game over) mode, the problem is usually connector related. Games that reset while in attract mode usually have connector related problems or low line voltage (below 115 volts).

Testing for Resets.
To narrow this down to a intermittent connection (points 1,2,3,4 above), or to a +5 volt filter cap, missing diode or switch problem, try the following. With the game off, remove fuses F2 and F3 from the power supply (solenoid and lamp matrix fuses). Now turn the game on and go into self test. Put the game in the "digits test" (which conveniently is the first self test), so that the displays are cycling all the different score display numbers. Now just walk away for a couple of hours or more (letting this test run overnight works well).

Upon returning, if the score digits are not cycling, then the game reset without any game play occuring. This means there is an intermittent problem (points 1,2,3,4 above). If the game is still in the digits test, then the reset problem is probably a bad +5/12 volt filter capacitor, broken coil diode, or a switch matrix problem.

Bad 5/12 volt Filter Cap.
A bad +5/12 volt filter capacitor will really only show its ugly head when the game is played. The coils turning on and off forces the +5 vdc filter cap to work harder. If it's bad, it should show pretty quickly in game play. Likewise for bad coil diodes, and switch matrix problems (though often switch matrix problems can be duplicated in the diagnostics switch matrix test).

Missing or Broken Coil Diode.
A missing or broken coil diode (especially a missing diode on any flipper coil) can really cause strange game behavior and resets. For example, a missing/broken flipper coil diode can cause the game to reset if one or both flipper buttons are pressed. A broken diode on another type of coil can cause a reset just when that device is used.

For example, a reader reported that the flippers caused the game to lock up on his Firepower. He went to the game's coil test, and noticed the middle right multiball saucer solenoid was not firing. He replaced that coil's diode (which fixed the saucer coil), and the flippers no longer caused the game to lock up.

Be sure there is a 1N4004 on *every* coil. A good way to test for a broken/cracked diode is to try grabbing the diode with your thumb and forefinger, and giving it a gentle tug. Often the body or lead of a diode can crack, and this will identify it. If there's any doubt though, just replace that diode with a new 1N4004 diode. They are inexpensive, and it's an easy job. Just remember that the banded side of the diode goes to the power lug/wire on the coil (the power wire is usually the thicker wire, and is "daisy chained" from one coil to another).

The 1N4004 coil diode mounted on a Firepower slingshot, showing the proper orientation of the diode and power wires.

Diodes can be tested with a DMM, but frankly it's not worth it, as one lead of the diode needs to be disconnected from the coil for a good test. To go through the work of removing one end of the diode, it's about as easy to just replace the questionable diode instead. But here's how to test a coil diode:
• Turn the game off.
• Unsolder or cut one end of the diode from the coil.
• Use a DMM set to the diode function.
• Put the black DMM lead on the banded side of the diode.
• Put the red DMM lead on the NON-banded side of the diode.
• .4 to .6 volts should be seen.
• Reverse the DMM leads, and a null reading should be seen.
• If these values are not seen, replace the diode with a new 1N4004 diode.

The Switch Matrix and Resets.
If there is a short in the switch matrix a bad diode on a playfield switch, or a mis-wired playfield switch, this can cause resets and strange game behavior too. For example, column one of all system3 to system7 games have the tilt and slam tilt switches. If another switch gets shorted in the same row or column as a tilt switch, strange game behavior can occur during game play as other switches are activiated in that row or column.

Summary.
The only way to fix the listed things above is *replacement* of parts! New 40 pin connectors between the driver and CPU boards, new chip sockets to replace the old "Scanbe" sockets, new power connector at CPU board 1J2, and new +5 volt filter capacitor. And while the CPU and driver boards are out, might as well resolder all the .156" male Molex connector pins on the edges of the boards, as these often crack.

Introduction.
In a working game, the first thing to remember on all coils and flashlamps is power is *alway* present at all coils/flashlamps. All these devices are waiting for is the backbox driver board to complete the their power circuit to ground, causing the coil or flashlamp to energize.

Essentially the driver board is a big computer controlled grounding plane. Through the game ROM program, the CPU, and the PIAs (Peripheral Interface Adaptors), the game can control which driver board transistor can "sink" a ground, and hence complete a particular coil's power path (causing the coil/flashlamp to energize for a short period of time).

The way the driving logic works is as so: the CPU, which is running the game ROM program, wants to energize a coil. It tells the a PIA (Peripheral Interface Adaptor) to turn on the appropriate coil. This in turn drives a 7408/7402 chip, which then turns on a small "pre-driver" 2N4401 transistor. So far this is all done with "logic level" 5 volts. Then the pre-driver transistor turns on a much bigger TIP120/TIP102 transistor. This final link in the chain is what ultimately completes the coil's path to ground, causing the 28 volt coil to energize momentarily.

A potential problem with this system is if ANY part in the chain shorts, everything else down the chain turns on, and a coil locks-on. Typically this is last link in the chain, the TIP120/TIP102 driver transistor, becoming "shorted" internally (because this device is in direct line with the 28 volt solenoid voltage, where the other devices are "buffered" from this voltage). But it could be any of the other parts too! (the 2N4401 pre-driver transistor, the 7408/7402 chip, or the PIA chip!) It could even be ALL these devices short on!

So instead of the CPU controlling the driver transistor (and hence its associated coil/flashlamp), the coil/flashlamp becomes lock-on (permanently energized), because the path to ground is shorted inside one or many of the controlling devices. So if a coil (or several coils) or flashlamps are locked-on, the TIP120/TIP102 is at minimum is usually the cause. But the big problem is if the TIP120/TIP102 driver transistor shorts, sometimes the "backlash" can ruin the parts behind it (2N4401, 7408/7402, PIA) that control the transistor.

All Coils Locked on - the Blanking Signal.
In Williams system3 to system7 games, there is one more reason a bunch of coils/flashlamps would be locked on. That would be if the blanking signal is not high, allowing all the coils to energize at power-on and stay energized. We really won't talk too much about that condition in this section, as that's really a failed CPU/Driver board issue (and not a failed coil/transistor). See the Dead CPU section for more info on that subject. Note if only a one or a few coils are energizing at power on, then there is probably a shorted driver board transistors, and NOT a problem with the blanking signal.

The blanking signal is a "flag" from the CPU board to the driver board. If the blanking signal is high (4 volts or greater), the CPU board is saying to the driver board, "Hey! I'm working and ready!" If the blanking signal does not go high, the driver board does not "wake up", and often this means all the game's coils will energize!

A low blanking signal can signify there is a CPU board problem. But there could also be a high CPU board blanking signal that gets "lost" while going over the 40 pin interboard connector, leading to the driver board!

The blanking circuit should go HIGH very soon after the machine is powered-on (almost instantaneous). When the blanking signal is LOW, it allows all the coils to energize automatically. In general, the blanking circuit reading can be taken at pin 37 of the 40-pin inter-board connector (4th pin from the left), and should be at least 4 volts. This is where the blanking signal goes from the CPU to the driver board.

Solenoid Power Circuit.
The 28 volt solenoid circuit consists of a bridge rectifier mounted on the backbox. Like the lamp rectifier, its a 35amp, 400 volt bridge rectifier. After that, the power goes to the power supply board, and thru a 47volt varistor used to protect the coils from a voltage spike (if the voltage goes above 47 volts, the MOV varistor shorts, which will blow the main solenoid fuse). There is also a 100 mfd filter capacitor.

The driver board driver transistors are the most probable source of solenoid problems. But an easy first test is to measure the voltage at connector 3J3 pins 6-9 on the power supply board, which should show about 28 volts DC. If there is no voltage, check the solenoid fuse F2. If there is a lower voltage, the backbox mounted bridge rectifier has probably partially failed. If the voltage is higher than 28 volts, don't worry about it (as long as it's not more than 47 volts!) The "unloaded" system should measure higher than the "loaded" 28 volts DC.

Flipper Power Circuit and the Flipper Relay.
Next to the GI circuit, this is the simplest circuit in the game. The only electronic part is the bridge rectifier that is shared with the solenoid circuit (discussed above). Note the flippers do not use a filter capacitor. On System3 and System4 games, 28 volts DC goes directly to the flippers from the backbox bridge rectifier, with the flipper fuse located under the playfield. Starting with Flash (System6), the flipper voltage is "passed through" the Power Supply board, with fuse F4 now protecting the flipper coil circuit, instead of a playfield mounted flipper fuse.

Remember later system7 games (Firepower2 and later) have a separate 50 volt power supply board for the 50 volt flippers. This upgraded flipper voltage was increased from 28 to 50 volts to give the flippers a bit more snap. But the rest of the coils in the game are still 28 volts.

If the flipper coils don't work or don't shut off after a games ends, there may be something wrong with the driver board mounted Z1 flipper relay (or the transistor and other components that drive the flipper relay, and these part number are the same for all system3 to system7 games). This is kind of a last thing to check, as flipper relay problems are not common. Test the 2N4401 transistor Q13 (positioned right next to the relay) with the testing procedures described in the Transistor Testing section of this guide. Also the 7402 chip at IC8, which drives transistor Q13 could be bad. There have even been reports of resistors R27 (4.7k 1/4 watt) and R26 (10k 1/4 watt) being bad, in addition to diode D1 (1N4001). Lastly test the flipper relay itself, as the relay does go bad (the driver board will need to be removed to do this). A 9 volt battery can be used on the relay's coil lugs (the two isolated lugs from the other 12). Use the battery and check if the relay actually pulls its armature in and out (it should click nicely). If a replacement relay is needed, this relay is a 4PDT (4 pole double throw), 40 ohm, 6 volt relay, and a suitable replacement can be found at Mouser.com, part #528-7810-1 (MagneCraft #W78CSX-1, $5.50).

Don't Forget the Grounding Strap.
In the backbox behind the backglass, there is a ground wire/strap which attaches to a wing nut. This ground strap is very important, and must be connected. On many system3 to system7 games, some features of the game won't work (or won't work properly) if it's not attached to the wing nut and the wing nut tightened. Also later games from Firepower on had an additional white-with-red trace grounding wire coming from the playfield that needs to be cinched under the wing nut along with the braided ground wire.

Remove Fuses F2 and F3 When Doing Intial Testing.
Be careful when testing an unknown game. At power-on, some coil may lock on and constantly energize. This will burn both the coil and its driver transistor. Until the CPU is working properly, it is wise to remove coil and lamp fuses F2 and F3 from power supply board to minimize problems.

The Coin Door Coin Lockout Coil.
On the coin door, there is a small relay sized coil known as the "coin lockout coil". When a system3 to system7 game is powered on, this coin lockout coil should always be energized! Yes that's right, the associated driver board transistor should always allow this coil to be "on", when the game is powered on.

When the coin lockout coil is de-energized, the game will reject money. This is done so if some (dumb) player inserts money into a powered-off game, their money is returned to the coin return shoot. Basically if the game is on, the coin lockout coil is energized. It is even energized when the game is in diagnostic mode (on most, but not all system3-system7 games). Note on some games, if the game is set to "free play" through the adjustments, the coin lockout coil will de-energize when the game is on.

Coin lockout coils were done away with during system11 I believe. Williams needed the transistor for other more important chores, like playfield devices.

Could the coin lockout coil be blowing the solenoid fuse? Yes! Since this coil is on *a lot*, it gets hot with time. The winding's wire bakes off its insulation, making adjacent windings short to each other. This reduces the resistance of the coin lockout coil from it's normal (about) 80 ohm resistance, to be lower. As a coil's resistance becomes lower, it draws more current, and becomes hotter. As it becomes hotter, it burns more winding insulation. It's a endless cycle until the coin lockout coil burns up. When a coil's resistance gets below about 2.5 ohms, it essentially becomes a "dead short", and this will blow the solenoid fuse.

This coil can be tested - Just put a DMM set to resistance on the coil lugs (with it's driver board connector J9 removed to isolate the coil) and check the resistance. It should be greater than 50 ohms. Note the driver board transistor that controls the coin lockout coils is Q45 (bottom row, furthest to the right). A good way to test this transistor is using the game's internal diagnostics and testing coil number 16 (the coin lockout coil will be energized during all of diagnostics on most system3-7 games, but when coil number 16 is tested, this coil should cycle on and off). Another way to test transistor 45 is with a DMM set to the diode function, and the game turned off (as described below).

Some good advice is to disconnect the coin door's coin lockout coil. This can be done by cutting the ground wire (wire going to the driver board) from the coin lockout coil. Then modify the coin door mech so the coin lockout coil is not needed (that is, if using the game with coins). This modification is very easy (involves bending or removing the coil trigger bar).

The problem with the coin lockout coil is it is old, and usually near death, often BUZZES loudly, consumes power (higher operating costs), and it only causes problems. And frankly, in a home environment, it's not needed! Even if operating the game for money, I would disconnect it (it's only a problem waiting to happen). If a player doesn't notice the game is off, and puts money in, that's their problem!

CPU Controlled Solenoids.
CPU controlled solenoids are obviously controlled only by the CPU, and the game ROM program that the CPU is running. CPU controlled coils also have a "one shot" type operation, with a percise energize time. By "one shot" I mean if their controlling trigger switch gets stuck on, the coil fires one time (one shot), de-energizes, and stays de-energized. So a stuck playfield switch only makes the device non-operational, opposed to locking the device on and letting it burn. CPU controlled solenoids are numbered one to 16 in the solenoid diagnostic test and schematics. The 16 CPU controlled solenoids are program activated by PIA IC5 via a 7408 chip and two transistors (2N4401 pre-driver and a TIP120/TIP102 driver).

The system3-7 CPU controlled solenoid schematic.

Special Solenoids.
Special solenoids on the other hand work differently than CPU controlled coils. Special solenoids are used in pop bumpers and slingshot kickers, and since they must act quickly, the CPU does not control them. Closing of a special solenoid's playfield trigger switch enables solenoid power directly through TTL (Transistor to Transistor) chip logic and two transistor, without any processing by the CPU chip. A second switch matrix switch is closed when a special solenoid pulls in, which tells the CPU to score the solenoid points (CPU controlled solenoids do not need this second switch). Hence the special solenoid trigger switches are not part of the switch matrix, where the scoring switch is. Note there are six special solenoids in the system3 to system7 driver board.

At the time, it was felt that the clock speed of the CPU was not fast enough to give quick acting pop bumpers and slingshot kickers, as the CPU was doing other things like monitoring the switch matrix and running the lamp matrix and score displays. Note though two games, Time Warp and Stellar Wars, used five pop bumpers and two slingshot kicker. Since there were only six special solenoids, something had to give on these two games. In Stellar Wars, the lower right pop bumper was a CPU controlled solenoid. On Time Warp both slingshot kickers where CPU controlled solenoids.

But the story doesn't end there with Special solenoids. The control of special solenoids on all system3 to system7 games is directly through playfield control via the playfield trigger switches. But interestingly, special solenoid can also be controlled by the CPU too. This can be seen when running the internal game diagnostics, and the game turns the special solenoids on and off in the coil test. Because of these "dual trigger" (two ways to turn on) functionality of the special solenoids, these can be more problematic than the other 16 "CPU controlled" coils on the game.

A special solenoid slingshot kicker on a Firepower. Note even this coil uses a 1N4004 diode (with the banded end connected to the power wire). In addition the playfield activition trigger switch has a 22 mfd polarized cap and a 100 ohm resistor in series.

Special solenoids use a 7408 chip, a 7402 chip, and two transistors (2N4401 pre-driver and a TIP120/TIP102 driver). This is one more TTL circuit than the CPU controlled coils use. A special solenoid operates if the playfield switch pulls one 7408 input low. The other 7408 input can be pulled low by the CPU via a PIA (and this is what is done in the diagnostic solenoid test). So a special solenoid could work in diagnostic test but not work in game mode (or vice versa). This confuses a lot of people because the diagnostics show a coil a "working", yet when playing the game the same coil does not respond.

Also the the special solenoid playfield switch trigger has a 100 ohm 1/2 watt resistor and a 22 mfd 100 volt electroylic capacitor (the positive lead connected to the resistor) in parallel to the switch. This is different than CPU controlled coils that use a switch matrix switch to turn them on (switch matrix switches only have a 1N4004 diode on the switch).

Again the thing about special solenoids that is really freaky is this: the diagnostics can show the special solenoids as working, but in game play they may not work! The opposite is also true; a special solenoid could work in the game, but not in diagnostics. This happens because there are two different and distinct triggers for the special solenoids. That is, playfield trigger for the special solenoids uses different hardware logic then the diagnostic trigger for special solenoids. This can be very confusing.

The logic flow for the special solenoids works like this: the PIA IC5 and the playfield trigger switch feed to the same 7408 chip (IC6/IC7). (Note the playfield trigger switch goes first thru a pullup 4.7k resistor (R1-R6) which sometimes go open or out of spec causing problems.) The 7808 is an 'OR' TTL chip, meaning if either of the switch input are triggered (playfield or PIA), the TTL output turns-on the special solenoid circuit engerizing the coil. The OR'ed 7808 trigger signal then goes to a 7402 chip (IC8/IC9), which goes to a 2N4401 pre-driver transistor, and finally to a TIP120 or TIP102 driver transistor (which ultimately sinks the ground and fires the coil). So if a special solenoid only works in game mode and not diagnostics, the problem has to be the 7408 chip or the PIA chip IC5. If the special solenoid only works in diagnostic mode and not game mode, the problem has to be the pullup 4.7k resistor (R1-R6), the 7408 chip, or the playfield switch (and associated cap/resistor on the switch) or connector for the playfield switch. If a special solenoid works with one trigger but not the other, the 7402 and everything connecting after it (pre-driver, driver transistors, coil, etc.) are fine.

The system3-7 Special Solenoid schematic. Note the dual inputs: either the playfield trigger switch, or the PIA.

To confuse things even more, the Special solenoids have yet another switch involved. This is the scoring switch, which is part of the switch matrix (unlike the special solenoid trigger switch). So each pop bumper and slingshot have a second physical switch mounted on the playfield device. This switch closes as the coil energizes. This switch matrix switch in turns tells the CPU to score the device (but does *not* tell the CPU to fire the coil). So if there's a pop bumper or slingshot that works fine (energizes), but does not score, often it's because this secondary switch matrix switch is mis-adjusted or broken.

Slingshots that Barely Fire - the Slingshot Resistor and Cap.
A reader reports having a Flash pinball where the slingshots act strange. If the pinball hits the slingshot rubber (or it is actuated manually), it barely fires and there is a small kick. But if both sling rubbers switches are manually touched together it works fine.

The solutions was to check the 22 mfd 25V cap and 100 ohm resistor in series (black wire to - side of cap, + side of cap to resistor, resistor to other side of switch) mounted on the slingshot switches. These make the slings fire quicker and faster. In this the resistor was broken on one side, and the capacitor was broken on the other side. Replaced all the bad parts and it works fine now.

Special Solenoids that work in the Game, but Don't in Diagnostics.
The special solenoids work fine while playing the game, but don't in the diagnostics. Should anyone really care? After all, the only use for the CPU control of the special solenoids is in the diagnostics. But I guess that's up to you to decide whether it should be fixed (after all, if the game plays, who cares?), but I'll try and explain why this could happen.

In diagnostics, the special solenoids are controlled by the CPU via PIA chips. Sounds simple enough, that's how the other 16 CPU controlled coils work. But it's not that simple, because unlike the other 16 CPU controlled coils which are controlled by PIA IC5 on the driver board, the special solenoids use *four* PIAs for their CPU control! Here's a logic chart:

Note one of the special solenoid controlling PIAs is on the CPU board, not the driver board! (Better check that 40 pin interboard connector.) So if the solenoid IC5 PIA was replaced thinking it would take care of the special solenoids in diagnostics, chances are 5 out of 6 that the problem will *not* be fixed! (Usually it's the 7408 chip anyway.) And the special solenoids are not controlled by the PIA's "normal" ports. Instead they use CA2 and CB2, which are two specialized ports on the PIA, at pins 19 and 39. Leon's test chip does test pins 19 and 39 of all the PIAs, but unfortunately the pulses are usually not as clear as testing the "normal" port at pins 2-17 of the PIAs.

Locked On Special Solenoids- The Trigger Switch, Cap, Resistor.
The bad thing about special solenoids is they are NOT a "one shot" type device. If a special solenoid playfield trigger switch gets permanently closed, it's associated coil "locks on", and stays energized. And it will stay energized until either a fuse blows, or the coil burns (and in the process burns up the coil's driver board transistor). It is actually quite common for even a momentarily locked on special solenoid to burn out its associated driver transistor, and even the 74xx chips and PIA (this seems to be a big problem with locked on pop bumpers). It was strange that Williams choose to *not* make the special solenoids "one shot", as even Gottlieb did on their non-CPU controlled "one shot" pop bumper driver boards. Eventually Williams did make all coils CPU controlled (with System11A), making everything "one shot".

So the moral of this story is to *always* check the special solenoid trigger switch on the playfield. Also be sure to check the 22mfd 100 volt capacitor and 100 ohm resistor that are wired in parallel to the switch (and of course the coil's 1N4004 diode). The resistor can short closed, essentially causing the playfield switch to be locked on. Same thing for the capacitor, which can also short internally causing its special solenoid to lock on. Note the resistor and capacitor can be removed, and the system will still work (the easiest way to do this is to just cut either lead of the resistor from its solder lug). This is a good first step if a special solenoid is locked on, as it removes another potential problem from the system. But remember if the playfield switch is stuck on or the resistor/capacitor is shorted, this could be the whole problem, and what ultimately caused the "domino affect" of ruining the driver board parts, the coil, etc. Also remember if the resistor and/or capacitor is cut for test, they should be replaced or re-attached. These were added to cause the special solenoid circuit to be "on" for a brief period of time after the special solenoid switch opens back up, in order to make the pop bumper "pop" better. It sort of fools the driver board into thinking the switch is actually staying closed longer than it really does, making the slingshot or pop bumper kick a bit harder. Sometimes sluggish pop bumpers or slingshots can be caused by its associated playfield switch's resitor or capacitor going open.

A pop bumper drawing showing the special solenoid Trigger switch (not in the switch matrix), and the scoring switch (which is in the switch matrix).Pic by Norbert Snicer.

Also remember the special solenoid trigger switch is *not* part of the switch matrix. So the game's switch matrix diagnostics can *not* be used to test the playfield special solenoid trigger switch.

There is a whole section about testing driver board transistor in the Checking Transistors section of this document. But outside of this, some other tests can also be used. If unsure about a coil and whether it works, try these simple tests, with the solenoid fuse F2 installed.

Remember, if a coil is locked on, check if it is a Special Solenoid (pop bumpers and slingshots). The special solenoids will "lock on" if their corresponding playfield activiation switch is stuck on or shorted. So a locked on special solenoid could be as simple as a permanently closed solenoid playfield switch.

Testing for Overall Solenoid Power.
If the coil does not fire, there may be no 28 volts from the power supply. For this test, the solenoid fuse F2 will need to be installed. Using a DMM set to DC volts, do the following:

• Put the DMM black lead on the power supply ground connector 3J4 pin 1.
• Put the DMM red lead on power supply board connector 3J3 pins6-9.
• Turn the game on.
• There should be 28 to 47 volts DC.

If there is no voltage, check solenoid fuse F2. If this fuse keeps blowing at power on, the backbox mounted 6BR2 solenoid bridge rectifier has probably shorted. If no voltage or low voltage, this could also be the solenoid bridge rectifier.

Testing for Good Coil Ohms.
If a coil has been over-heated (locked-on) previously, the coil windings can get hot enough to burn their painted enamel insulation. If this happens, the windings can short, causing the overall resistance of a coil to be too low (essentially making the coil a "short"). This can then stress the driver transistor, eventually blowing it.

To check a coil for this problem, put a DMM on the low ohm setting, and put each DMM lead on each lug of the coil. It should read 3 to 150 ohms. If it is any lower than about 2.5 ohms, the coil probably has an internal short and should be replaced.

Another indication that a coil has been heat stressed is if its internal nylon sleeve can be removed from the coil. If this coil sleeve can not be easily removed, chances are good the coil has gotten hot enough to expand, and the coil should be replaced.

Remember when replacing a coil, the thicker POWER wire(s) go to the coil lug with the banded side of the diode attached. The thinner ground wire (which goes to the driver board) goes to the coil lug with the non-banded side of the diode attached.

Testing for Power at a Coil/Flashlamp.
If the coil does not fire, there may be no power at that coil or flashlamp. For this test, solenoid fuse F2 will need to be installed. Using a DMM set to DC volts, do the following:

• Lift the playfield up on the game.
• Turn the game on and let it go into attract mode.
• Put the DMM black lead on ground (the metal side rail).
• Put the DMM red lead on EITHER coil lug or flashlamp lug.
• Either lug should show 28 volts (for either a coil or flashlamp, as flashlamp power is the same 28 volt power source).

If only one lug shows voltage, the coil or flashlamp is bad (it has a broken winding). If neither lug shows voltage, check "upstream" and see if the daisy-chained thicker power wire broke off another coil/flashlamp in the chain.

Testing the Coil/flashlamp.
If a coil or flashlamp is not firing, and with power at the coil, this test will check if the coil or flashlamp is capable of firing. For this test, solenoid fuse F2 will need to be installed.

• Lift the playfield up on the game.
• Turn the game on and let it go into attract mode.
• Using an alligator test lead, attach one end to ground (the game's metal side rail).
• Momentarily touch the other end of the alligator test lead to the GROUND coil or flashlamp lug. The ground coil lug is the lug with the non-banded side of the 1N4004 diode attached (all coils should have a 1N4004 diode!), and the thinner wire attached. The ground lug on a flashlamp is the lug that goes to the resistors (usually the tip of the flashlamp socket).

The coil or flashlamp should fire. If the power lug is accidently touched with the alligator clip, the solenoid fuse will probably blow, and the game will probably reboot. If this happens, replace the fuse and try again (touching the correct coil/flashlamp lug!)

IMPORTANT: While doing this, note the 1N4004 diode on the coil. Make sure it is in good shape, not cracked or damaged, and is connected to the coil lugs. More info on this diode is below. Note there is no diode used on flashlamps.

Testing the Wiring from the Driver Board to the Coil/flashlamp.
For a non-working coil/flashlamp, now it is verified there is power at the device, and the coil/flashlamp can actually fire. It's time to see if the wiring from the coil's non-banded diode lug (or from the flashlamp's resistor board) goes uninterupted to the driver board.

• Check the schematics or operator's manual and figure out which TIP120/TIP102 transistor number goes to the coil/flashlamp in question. Or if schematics are not available, find the non-power wire color at the device. Then go to the driver board and find that same wire color at the connectors on the left edge of the driver board. Using a DMM set to continuity, put one DMM lead on that driver board connector pin and touch the other DMM lead to all the metal tabs of the driver board left-side TIP120 transistors. This will identify which transistor drives the questionable device.
• With the game on and in attract mode, use an alligator test lead, and connect one end to ground in the backbox.
• Using the other end of the alligator test lead, momentarily touch the metal tab on the coil/flashlamp's transistor. This should fire the coil/flashlamp in question.

Do this should fire the coil/flashlamp. If it does, the wiring from the driver board to the coil is OK. If it does not fire, chances are good there is a bad backbox/cabinet connector (common as the male connector header pin's solder joints often crack where soldered to the driver board), or the wire is cut somewhere between the backbox and the coil. If the problem is a non-working flashlamp, make sure to check the under-playfield resistors for that flashlamp. Because the 12 volt flashlamp is run at 28 volt solenoid voltage, there are two resistors used as additonal resistive "load" so the 12 volt flasher doesn't burn out at 28 volts (one resistor is a "keep alive", the other is used when the lamp is "fired"). If the "fired" resistor goes open, the flash lamp will never work.

Everything Checks Out So Far, But the Coil/Flashlamp Still Doesn't Work.
Remember, if a coil is locked on, check if it is a Special Solenoid (pop bumpers and slingshots). The special solenoids will "lock on" if their corresponding playfield activiation switch is stuck on or shorted. So a locked on special solenoid could be as simple as a permanently closed solenoid playfield switch.

At this point, there is a driver board issue. Power is at the device, and the wiring gets to the driver board, but the coil or flashlamp will still not fire (or is locked on). This is a good indication either the driver transistor has failed, or it's driving 7408 chip has failed, or even the driver board solenoid PIA at IC5 has failed.

Check the Driver Board Male Header Pin Solder Joints.
If the driver board is removed, it is really a good idea at this point to re-solder the header pin connectors on the Driver board (obviously the driver board needs to be removed for this work.) Heat the joints with a soldering iron until the solder melts, and add some new solder. Sometimes it's difficult to get the solder to stick to encompass the head pin "butts". So an even better method (though more involved) is to remove the old solder using a desoldering tool, and then resoldering the connector pin with new solder. This is a good idea because the old solder often does not stick well to the connector pins "butts". But attempting to diagnose problems without first doing this is often a waste of time, because the driver board flexs as it is removed from the 40 pin interboard connector or as connectors are removed/attached. This flexing causes cracks in the male header pin solder joints, causing intermittent or non-working connections.

Testing the Driver Board Transistors.
This should be done for a non-working or locked on coil or flashlamp. The driver board does not need to be removed for this test, but it does make the job easier. This procedure is listed in the Checking Transistors section of this document too. All transistors are tested using the diode function of a DMM (Digital Multi Meter).

Important Note: Testing transistors (or chips) using the methods below does not give 100% proof that a transistor is good or bad. It's probably about 95% accurate, but it is not 100% accurate (especially if the transistor is mounted in a circuit board). I will say this - if a transistor tests as "bad", then it's bad (or the TTL chip that feeds it is bad). But if the transistor tests as "good" that does not necessarily mean the transistor is good.

Testing the TIP120 (or TIP102).
Solenoid driver transistor. Always replace TIP120 with TIP102.
• Black DMM lead on metal tab (or center leg).
• Red DMM lead on either leg, one at a time.
• .4 to .6 volts seen.

Testing the 2N4401.
Pre-driver for TIP102 (or TIP102).

• Red DMM lead on center leg.
• Black DMM lead on either leg, one at a time.
• .4 to .6 volts seen.

If the driving TIP120 transistor is bad, be sure to replace it with a more robust TIP102 transistor. Also make sure to replace the pre-driver 2N4401 transistor that accompanies the TIP120/TIP102.

At this point, it is best to test the driving 7408/7402 chip. It only takes a moment, and saves a lot of work if this chip is damaged. Also a bad 7408/7402 can cause a driving transistor to test as "bad".

Testing the 7408/7402 Chips and Solenoid PIA.
At this point, the TIP120/TIP102 and pre-driver 2N4401 are tested/replaced, but the coil/flashlamp is still locked on. Now it's time to test the 7408/7402 driver chips.

No need to test this 7408 chip! The 7408 in the middle is physically bubbled up and can easily be seen as "bad". It can be counted on that the 2N4401 pre-driver and TIP120/TIP102 driver transistors are blown too! Just hope the IC5 solenoid PIA chip survived.

These chips can also be tested with a DMM set to the diode function and the game off. For a 7408, put the red lead on ground (pin 7), and put the black lead on pins 1,2,3, 4,5,6, 8,9,10, 11,12,13. A reading of of .4 to .6 should be seen for each pin (a reading lower than .2 is a big sign of a bad chip).

Likewise a 7402 (used for special solenoids) can be tested in the same manner. With the game off. For a 7402, put the red lead on ground (pin 7), and put the black lead on pins 1,2,3, 4,5,6, 8,9,10, 11,12,13. A reading of of .4 to .6 should be seen for each pin (a reading lower than .2 is a big sign of a bad chip).

Remember though, testing TTL chip mounted in a circuit board using a DMM's diode test can give false readings. If the chip is socketed, it's better to use the DMM diode test with the chip removed from the circuit. An even better test (with the board powered on) is to use a logic probe and to compare similar TTL chips. That is, compare two (or more) similar 7408 or 7402 TTL chips which both control solenoids (see the schematics).

TIP Transistor & TTL Checks Good, but Coil Locked On - Now What?
In the case of all coil *except* the special solenoids, the only thing left is the PIA IC5. Luckily in the case of CPU controlled coils this is easy to test. Have the solenoid power fuse removed. Using a logic probe, the PIA IC5 outputs can be checked. With the game in attract mode, all coil outputs from the PIA IC5 should be LOW (except for the coindoor lockout coil), meaning the coil is NOT energized. If the PIA outputs are missing or high, the associated coil will be locked on (remember the coindoor lockout coil will be ON, unless the game is at maximum allowed credits).

The TTL 7408 is a two input, one output AND gate. This means BOTH input signals must be HIGH for the AND gate to be completed, making the output AND gate signal HIGH (and energizing the coil). If the game is successfully booted, the Blanking signal is already high, so one of the AND inputs is high. Now the 7408 is waiting for the PIA to make the other input AND signal momentarily high to fire the associated coil.

In the chart below the first listed TTL is the AND gate output. The next pin number (after the ":") is the AND input from the PIA. The last TTL pin number is the blanking signal (which should be high in a booted game). The output TTL pin (first listed TTL pin) should be low with the game in attract mode. If the TTL input pin coming from the PIA is low, the blanking input TTL pin is high, but the output TTL pin is high or missing, then the TTL 7408 chip is bad.

Below is a chart of the IC5 PIA and TTL outputs which should be checked with the logic probe for a "low" signal (game powered on and in attract mode).

The system3-7 CPU controlled solenoid schematic (PIA, AND gate, transistors).

Coil#	Connector	TIP 120	2n4401	TTL (output, in PIA, in Blank)	PIA Output (low)
Coil 1	J11 pin 4	Q15	Q14	IC1 pin 8:10,9	IC5 pin 2
Coil 2	J11 pin 5	Q17	Q16	IC1 pin 11:12,13	IC5 pin 3
Coil 3	J11 pin 7	Q17	Q16	IC1 pin 6:4,5	IC5 pin 4
Coil 4	J11 pin 8	Q21	Q20	IC1 pin 3:1,2	IC5 pin 5
Coil 5	J11 pin 9	Q23	Q22	IC2 pin 8:10,9	IC5 pin 6
Coil 6	J11 pin 3	Q25	Q24	IC2 pin 11:12,13	IC5 pin 7
Coil 7	J11 pin 2	Q27	Q26	IC2 pin 6:4,5	IC5 pin 8
Coil 8	J11 pin 1	Q29	Q28	IC2 pin 3:1,2	IC5 pin 9
Coil 9	J9 pin 9	Q31	Q30	IC3 pin 8:10,9	IC5 pin 10
Coil 10	J9 pin 7	Q33	Q32	IC3 pin 11:12,13	IC5 pin 11
Coil 11	J9 pin 1	Q35	Q34	IC3 pin 6:4,5	IC5 pin 12
Coil 12	J9 pin 2	Q37	Q36	IC3 pin 3:1,2	IC5 pin 13
Coil 13	J9 pin 3	Q39	Q38	IC4 pin 8:10,9	IC5 pin 14
Coil 14	J9 pin 4	Q41	Q40	IC4 pin 11:12,13	IC5 pin 15
Coil 15	J9 pin 5	Q43	Q42	IC4 pin 6:4,5	IC5 pin 16
Lockout	J9 pin 6	Q45	Q44	IC4 pin 3:1,2	IC5 pin 17*

*Unless game is at maximum allowed credits, the coin door lockout
PIA output will be high.

Leon Test EPROM could also be used for this test, but frankly I find that not necessary. It's just easier to be running the game code in attract mode and testing the outputs with a logic probe. But the Leon test chip procedure is fully described in the Dead/CPU driver board sub-section, CPU board is working, Install the Driver board. This shows how to test the PIA using a "tester LED" and Leon's test chip.

FlashLamp Problems.
Flashlamps are controlled as solenoids, and are wired in series (if there is more than one flashlamp fired by a single driving transistor). The flashlamps are "doubled up" and wired in series so that the 28 volt solenoid voltage can be used on the 14 volt flasher bulbs (two times 14 equals 28 volts). But the problem with this is if one flashlamp burns out, the other flashlamp will not work!

The resistor board for the flashlamp. The large 330 ohm 2 watt resistor is permanently connected between the flash lamp & ground. This keeps the flashlamp's filiment warm while the game is on, letting 12 volts to the bulb all the time through the 330 ohm resistor (this increase bulb life by keeping the filament warm). When the flashlamp is fired by the game, ground is then completed through the small 1 ohm (or 5 ohm) resistor, and the flashlamp turns on brightly. Electricity takes the path of least resistance, going through the 1 ohm resistor instead of the 330 ohm resistor. The 330 ohm resistor is often burnt or desolders itself from its board because power is going through it all the time (except when the flash bulb actually flashes). This game is Firepower. Williams used this bulb warming approach through System 11, but abandoned it with WPC.

Flashers also have two resistors connected to them, one large 330 ohm 2watt, and one small 1 ohm (or 5 ohm) 1/2 watt. When the flash lamps are not lit, the path to ground for the flash lamps is completed via the large 330 ohm and smaller 1 ohm resistors together. This keeps the bulb filiments warm (and less likely to burn out and also more likely to give a BRIGHT flash). On some flashlamps, they can look like they are glowing slightly when not in use. A cold flashlamp would take too long to get bright, so the flash would have less impact, so that's why Williams did this.

When the driver board transistor is turned on, the ground path is switched directly through the driver board, and the 330 ohm resistor is essentially eliminated from the circuit (because current will take the path of least resistance). Note the 1 ohm resistor is still utilized.

If a flash lamp is dull or sluggish, check the 330 ohm heater resistor. These resistors do burn and break (or get cold solder joints, or just fall off their solder terminal!), not allowing the flash lamp to "pre-heat". If this happens, it won't pre-heat the flash lamp, and the flasher may not flash! Also if flash lamps burn out often, the 330 ohm resistor could be bad. Be sure to check the 1 ohm (or 5 ohm) resistor too, as these can go open, and neither flashlamp will work.

The wiring for Flashlamps and Coils. Note the two flashlamps in series, and the 330 ohm resistor path to ground, that keeps the flashlamps "warm" (and dim). Then when the driver board ground path is used, the flashlamps turn on brightly, as the 330 ohm resistor ground path is negated.

The Coil Diodes and Why they are Important.
After testing or replacing a driver board transistor, it is important to examine the coil in the game. If any coil (especially the one that was just locked on) has a bad diode, this can almost instantly kill its associated driver transistor! The coil diode prevents a coil's collapsing voltage from "backwashing" to the driver board, damaging the driver transistor.

Since you spent the time to test/replace the bad driver board transistors, it only makes sense to also check for bad coil diodes. Since these 1N4004 diodes are mounted right to the coils under the playfield, vibration can crack or damage them.

The best way to test a coil diode is to just grab the diode by its body with the forefinger and thumb, and gently give it a pull. If the diode has a cracked body or broken lead, it should be pretty easy to see.

The 1N4004 coil diode mounted on a Firepower slingshot, showing the proper orientation of the diode and power wires.

Coil diodes (1N4004) can be tested with a DMM set to the diode function:
• Turn the game off.
• Unsolder or cut one end of the diode from the coil.
• Use a DMM set to the diode function.
• Put the blank DMM lead on the banded side of the diode.
• Put the red DMM lead on the NON-banded side of the diode.
• .4 to .6 volts should be seen.
• Reverse the DMM leads, and a null reading should be seen.
• If these values are not seen, replace the diode with a new 1N4004 diode.

If a new diode is needed, remember to install it with the diode's band on the power lug of the coil! It usually pretty easy to tell which is the power lug of a coil. The power wire, which daisy chains from coil to coil, is usually the thicker wire on a coil lug. The banded lead of the 1N4004 diode should be connected to the coil lug with this thicker daisy chained power wire attached. The non-banded end of the diode attaches to the coil lug with the thinner wire, which leads to the driver board transistor, and ultimately ground.

Introduction.
Remember, there are GI (General Illumination) lamps, and CPU controlled (lamp matrix) lamps. The GI lamps come on as soon as the game power is turned on. And these lamps generally do not turn off (except on Blackout, Scorpion and System7 games, where there is a GI lamp relay to toggle all the GI lamps on and off). The CPU controlled lamp matrix, when the game is in attract mode (game over), will turn playfield and backbox lamps on and off. The CPU controlled lamps also work during game play, to light certain features to help the player.

The CPU controlled lamps (the "lamp matrix") uses +18 volts DC to drive the CPU controlled lamps. If you're asking, "how do they use 18 volts to light 6.3 volt bulbs?", you would be asking a good question. While the lamp power supply outputs a constant 18 volts DC from the backbox mounted bridge rectifier and filter capacitor, the driver board "pulses" the 18 volts to the lamps. This turns the lamps on and off very quickly, so that they never get to full brightness, and are only on about 1/3 of the time (which roughly works out to about 6 volts). Turning the bulbs off and on like this increases light bulb life, which is a nice feature since most operators don't change burnt out lamps!

Important note about the lamp matrix: because the game is constantly pulsing the lamp matrix to bring the 18 volts down to about 6 volts, these games should NEVER be left on when they are "locked up". Because if they are locked up, the lamp matrix is not strobing, which can burn out the playfield lamps and COOK the driver board. The heat can get so bad on a driver board, that it will start to desolder parts!

The lamp matrix power supply has only three components: a backbox mounted 35 amp 400 volt bridge rectifier, and very large 30,000 mfd filter capacitor, and a fuse on the power supply board (F3).

There are some consistent lamp numbers from game to game. For example, all system3 to system6 games consistently used lamp column8 for the same functions (player up, tilt, game over, etc.) With system7, Williams basically moved column8 to column1. And with the last three system7 games (FirepowerII, Laser Cue, Starlight), this changed yet again (still using column1, but the row order changed). Below are the consistent lamps used in system3-system6 and system7 (except Joust, FirepowerII, Laser Cue, Starlight) lamp matrix:

Column/ Row	Col. 1 Yel-Brn 2J5-8	Col. 2 Yel-Red 2J5-9	Col. 3 Yel-Orn 2J5-6	Col. 4 Yel-Blk 2J5-7	Col. 5 Yel-Grn 2J5-3	Col. 6 Yel-Blu 2J5-5	Col. 7 Yel-Vio 2J5-1	Col. 8 Yel-Gry 2J5-2
Row 1 Red-Brn 2J7-1	#1 Extra Ball (sys7*)	#9	#17	#25	#33	#41	#49	#57 Player1 Up (sys3-6)
Row 2 Red-Blk 2J7-2	#2 Ball in Play (sys7*)	#10	#18	#26	#34	#42	#50	#58 Player2 Up (sys3-6)
Row 3 Red-Orn 2J7-3	#3 Tilt (sys7*)	#11	#19	#27	#35	#43	#51	#59 Player3 Up (sys3-6)
Row 4 Red-Yel 2J7-4	#4 Game Over (sys7*)	#12	#20	#28	#36	#44	#52	#60 Player4 Up (sys3-6)
Row 5 Red-Grn 2J7-5	#5 Match (sys7*)	#13	#21	#29	#37	#45	#53	#61 Tilt (sys3-6)
Row 6 Red-Blu 2J7-6	#6 Hi-Score (sys7*)	#14	#22	#30	#38	#46	#54	#62 Game Over (sys3-6)
Row 7 Red-Vio 2J7-9	#7	#15	#23	#31	#39	#47	#55	#63 Shoot Again (sys3-6)
Row 8 Red-Gry 2J7-8	#8	#16	#24	#32	#40	#48	#56	#64 Hi-Score (sys3-6)

* Except Joust, Firepower II, Laser Cue, Starlight.

All the CPU Controlled Lamps Do Not Work.
Most CPU controlled lamp problems are driver board associated. However if all the CPU controlled lamps are off and everything else is working, check power supply fuse F3 and the voltage coming out of the power supply.

Using a DMM, measure the voltage from power supply connector 3J4 pin 5 to 3J4 pin 1 (ground). There should be 18 volts DC. If there is no voltage (and fuse F3 is good), then chances are good that the backbox mounted lamp matrix bridge rectifier 6BR1 has failed.

A Row or Column of Lamps does not Work, or is Locked On.
This problem is usually driver board related. If a row or column is not working at all, the first thing to try is to resolder the .156" Molex male header pins on the driver board. The solder joints on these often crack (from insertion/removal of the connectors). This would include these driver board connectors:

• 2J4 (lamp matrix power)
• 2J5 (lamp matrix columns)
• 2J6 (lamp matrix ground)
• 2J7 (lamp matrix rows)

The next thing to suspect are the column/row transistors. These can be tested with a DMM set to the diode function and the game turned off. Keep in mind that column transistors die more than row transistors.

Important Note: Testing transistors (or chips) using the methods below does not give 100% proof that the component is good or bad! It's probably about 95% accurate, but it is not 100% accurate (especially with the transistor soldered into a board).

Lamp Columns (drive/strobe): test the TIP42, game off.
Q63, Q65, Q67, Q69, Q71, Q73, Q75, Q77. Using a DMM set to the Diode function:

• Orient the transistor's writing facing towards you.
• Black DMM lead on *left* leg (base) of transistor.
• Red DMM on center leg (or metal tab), .4 to .6 volts seen.
• Red DMM on left leg, .4 to .6 volts seen.

Lamp Rows: test the 2N6122 (or TIP41), game off.
Q47, Q49, Q51, Q53, Q55, Q57, Q59, Q61. Using a DMM set to the Diode function:

• Orient the transistor's writing facing towards you.
• Read DMM lead on the *left* leg (base) of transistor.
• Red DMM lead on the center (collector) leg (or metal tab), .4 to .6 volts seen.
• Red DMM lead on the right (emitter) leg, .4 to .6 volts seen.

Driver board or Playfield Problem?
Say you have a game where, in attract mode, colums 4 through 8 are very bright and the top four resistors on lower right side of driver board are getting warm. If you start a game and some lamp matrix lights stay locked-on, and some will still strobe like in attract mode. Is the problem on the playfield (shorted socket diode, mis-wired, or shorted lamp socket), or on the driver board?

To determine where the problem is, with the game on, remove the lamp column connector 2J5 and lamp row connector 2J7 from the driver board (the row and column connectors). Leave the lamp power 2J4 and lamp ground 2J6 connectors in place. Jump any one of the four overly-bright columns pins on 2J5 to any lamp row connector pin on 2J7 using two alligator clip leads and a light bulb (#47 or #44). If this single bulb is still overly bright, then the problem is on the driver board. If the lamp lights normally, there are two lamp column wires shorted together somewhere on the playfield.

Testing a Lamp Row/Colums with the Game On.
Another way to test the lamp rows (and indirectly the columns) is to do this:

• Turn the game on.
• Press the manual-down/auto-up coin door button to manual-down.
• Press the advance coin door button once. The score displays should go blank.
• Press the advance coin door button again. The score displays should all show zeros.
• Using a alligator test lead, attach one end to ground (the grounding braid in the bottom of the backbox or pin 40 of the interboard connector).
• Touch the other end of the alligator test lead to any one of the driver board transistors Q47, Q49, Q51, Q53, Q55, Q57, Q59 or Q61 (these are all in a vertical row in about the center of the driver board).
• All the corresponding playfield lamp matrix row lights should all turn on (eight lamps in all). If less than eight light, refer to the operator's guide and see which lamps in the particular row are not turning on, and make a note of it.
• Move the alligator test lead to the next lamp matrix row transistor to test the next eight row lamps.

If several lamps did not turn on, check the operator's manual and see if all eight lamps are in the same column or row. Note this does not test the row or column transistors themselves. It just tests everything from the driver board to the playfield. Also do NOT repeat this test for the *column* transistors! Doing that will blow the lamp matrix fuse.

Pre-Drivers: test the 2N6427 (or MPSA14), game off.
Columns: Q61, Q64, Q66, Q68, Q70, Q72, Q74, Q76. Rows: Q46, Q48, Q50, Q52, Q54, Q56, Q58, Q60. These pre-drive both the above TIP42 and 2N6122 transistors. Using a DMM set to the Diode function:

• Red DMM lead on middle leg.
• Black DMM lead on right leg, 1.0 to 1.3 volts seen.
• Black DMM lead on left leg, .6 to .8 volts seen.

Lamp Row(s) Stuck On - Troublesome 7406 Chip IC19.
This is a very common problem with system3 to system7 games, where one or multiple lamp rows are stuck on. In my experience, it is usually not the row transistor(s) that are the problem. It is usually the 7406 chip at IC19 on the driver board. This chip handles the logic for six of the eight lamp rows (the other two rows are handled by IC12).

A lamp matrix lamp. Note the wiring of the row and column wires, and the orientation of the diode.

One Lamp Does not Work.
Assuming the bulb is not burnt out, here are some things to check:
• Check the lamp socket. Yes sockets do go bad. With time, the fiber insulators shrink, allowing air to corrode the parts, and the socket does not make contact to the solder lugs.
• Also check for a shorted lamp socket. This can happen easily when doing other repairs. Often a shorted lamp socket will usually short out other lamps in the same row/column too.
• A broken or open lamp diode. There is a 1N4001 diode mounted on each lamp socket. If this diode is broken, missing or has gone open, the lamp will not work! There are rare cases that when a lamp burns out, it also burns out its diode too.
• The lamp row and column wires are "daisy chained" from socket to socket. Has the daisy chain broken "up stream?" This will cause all the lamps "down stream" to not work.
• Check for a shorted diode. This does not happen as often as open diodes, but its worth checking. Shorted diodes can happen if lamp matrix light bulbs are changed with the game on, and the lamp drive is accidentally grounded through the diode. A shorted diode usually causes one or more lamps to be ON at the same time.

Using a Logic Probe to Test the Columns/Rows.
Turn the game on and put it in the lamp matrix test, with the lamp matrix fuse F3 installed. This will turn all the computer controlled lamps on and off about every second. Now remove the driver board connectors 2J5 (lamp columns) and 2J7 (lamp rows). This will take the playfield out of the picture (where there could be a row/column short).

Put the logic probe on each pin on 2J5 (columns). The pins should be constantly pulsing. If any pin is not pulsing, its probably a bad TIP42 transistor (Q63,Q65,Q67,Q69, Q71,Q73,Q75,Q77), or the pre-driver 2N6427 (Q61,Q64,Q66,Q68, Q70,Q72,Q74,Q76).

To test the lamp row is similar. Again with the game in the lamp matrix test, use the logic probe on each pin of 2J7 (lamp rows). Each pin will pulse in time, turning on and off about every second (just like the playfield lamps flashed before the lamp connectors were removed). If any pin is not pulsing, its probably a bad 2N6122 transistor at Q47,Q49,Q51,Q53, Q55,Q57,Q59,Q61. Also it could be the pre-driver 2N6427 transistors at Q46,Q48,Q50,Q52, Q54,Q56,Q58,Q60.

The 7408 Lamp Column & 7406 Lamp Row Chips.
If a row or column is still locked on or not working, next look at the 7408 chips that drive the lamp columns. These are at IC13 and IC14. Also there 7406 lamp row chips at IC12 and IC19. The IC12/IC19 lamp row 7406 buffer chips actually fail quite often, compared to the lamp column chips.

These chips can be tested with a DMM set to the diode function and the game off. For the 7408 at IC13/IC14, put the red lead on ground (pin 7), and put the black lead on pins 1,2,3, 4,5,6, 8,9,10, 11,12,13. A reading of of .4 to .6 should be seen for each pin (a reading lower than .2 is a big sign of a bad chip).

Likewise the 7406 at IC12/IC19 can be tested in the same manner. With the game off, put the DMM's red lead on ground (pin 7) and put the black lead on pins 1,2, 5,6, 8,9, 10,11, 12,13. Again a reading of of .5 to .7 should be seen for each pin (a reading lower than .2 is a big sign of a bad chip).

Remember though, testing TTL chip mounted in a circuit board using a DMM's diode test can give false readings. If the chip is socketed, it's better to use the DMM diode test with the chip removed from the circuit. An even better test (with the board powered on) is to use a logic probe and to compare similar TTL chips. That is, compare two (or more) similar 7408 or 7406 TTL chips which both control lamps (see the schematics).

The Lamp Matrix PIA at IC10.
Though rare, there is a chance the lamp matrix 6821 PIA on the driver board at IC10 has failed. I would really make sure though that all the row/column transistors and 7406/7408 chips are not bad first (they are much more likely to fail).

Really the only way to test this chip is to use Leon's test EPROM chip and a "tester LED". This is best done with the CPU and driver board removed from the game, and powered up on the work bench with a computer power supply (as described in the Fixing a Dead CPU/Driver board section). If this is done in a game, remove power supply fuses F2 and F3, the driver board connectors at 2J4, 2J5 and 2J7.

Lamp Matrix Strobe (Column) Test (Connector 2J5).
To test the lamp matrix columns, power has to be applied to any pin of driver board connector 2J4. Normally this is +18 volts, but for our test, +5 volts will work fine. Using an alligator test clip, connect +5 volts (TP9 on system6/7 CPU board, or interconnector pin 1 on the far right) to any pin of driver board connector 2J4.

In addition, the connectors at both 2J5 and 2J7 need to be attached from the game. If testing "on the bench", an alternative method can be used (see below).

Now connect the tester LED's non-resistor lead to +5 volts. Using the resistor lead of the tester LED, touch each pin of driver board connector 2J5. The tester LED should alternate on and off, in unison with the blinking LEDs on the CPU board.

If the CPU/driver board combo is on a bench with no access to the playfield connectors 2J5 and 2J7, another method must be used. With the tester LED's non-resistor end connected to +5 volts, touch the tester LED's resistor end to the left most leg of each transistor Q62, Q64, Q66, Q68, Q70, Q72, Q74 and Q76 (the small transistors along the right edge of the driver board). The tester LED should alternate on and off, in unison with the blinking LEDs on the CPU board (the tester LED will not work directly on connector 2J5 without the playfield connectors 2J5/2J7).

If the alternating signal is missing, yet all the IC10 lamp PIA signals are present, check the inputs of IC13 or IC14 (7408) on the driver board (pins 1,2,4,5,9,10,12,13 of IC13 and IC14). If there is no input signal, there is a bad TIP42 (Q63,Q65,Q67,Q69, Q71,Q73,Q75,Q77) driver transistor or 2N6472 (Q62,64,66,68, 70,72,74,76) pre-driver transistor feeding the chip. Then check the output signals of IC13 and IC14 (pins 3,6,8,11). If the input signal is turning on and off, but there is no output signal, the chip is bad. Note the output signal from the chip may be very short.

Lamp Matrix Row Test (Connector 2J7).
This test also requires +5 volts power to any pin of driver board connector 2J4. Normally this is +18 volts, but for our test, +5 volts will work fine. Using an alligator test clip, connect +5 volts (TP9 on system6/7 CPU board or interconnector pin 1 on the far right) to any pin of driver board connector 2J4.

In addition, this test also requires a ground connection to any pin of driver board connector 2J6 (if the boards are installed in the game, just have the game connector attached at 2J6).

Once power and ground are applied to the lamp matrix, now connect the tester LED's non-resistor lead to +5 volts. Using the resistor lead of the tester LED, probe on each pin of driver board connector 2J7. The tester LED should alternate on and off, in unison with the blinking LEDs on the CPU board.

If the alternating signal is missing on any connector 2J7 pin, yet all the IC10 PIA signals are present, check the outputs of IC19 or IC12 (7406) on the driver board (pins 2,4,6,8,10,12 of IC19 and pins 2,4 of IC12). If there is no output signal, the chip is bad. If the output is good, there is a bad 2N5060, 2N6427 or 2N6122 transistor.

Should the Big Lamp Matrix Capacitor be Replaced?
They are hard to find and expensive, so unless its leaking and/or bulging, I would not suggest replacing the large backbox mounted lamp matrix filter capacitor. If fuse F3 is good, and the lamp matrix bridge rectifier is good, it's really the only component left (other than the transformer itself). So check the AC voltage coming out of the transformer before replacing this large capacitor.

Fixing the Eight Large Burnt Lamp Matrix Resistors.
To fix the large burnt lamp matrix resistors, a couple things can be done. First, replace these eight driver board R149-R156 resistors with 27 ohm 5 watt sand or ceramic wire wound resistors. Also make sure to install the new resistors about 1/4" off the circuit board to allow better air flow around them. Another good idea is to use #47 light bulbs for the feature lamps, as this will decrease feature lamp power consumption by about 40%!

Yet another option to fix the burnt resistors is an idea documented by C.Eddy. He replaces the eight TIP42 lamp matrix transistors (Q63, Q65, Q67, Q69, Q71, Q73, Q75, Q77) with IRF9z34N mosfets. The MOS-FETs are installed oriented just like the TIP42 transistors. And the mosfets only need a tiny amount of current to drive them (compared to the TIP42 transistor), hence the large power resistors at R149-R156 never get hot. Because of this there is no need to replace the large resistors (the old burnt ones can be left installed, unless they are open). Heck if the TIP42s are replaced with Irf9z34n mosfets the power resistors R149-156 can even be replaced with jumper wires or zero ohm resistors.

System3 to System7 games has a switch matrix of eight columns and eight rows that allows up to 64 individual switches per game. The CPU/Driver board will "strobe" (send a voltage) a switch column, and then read the switch rows (inputs) to see which switches are closed and returning current. All pinball manufacturers uses this style of switch matrix (even Gottlieb!)

Special Solenoid Switches Not in the Switch Matrix.
Note there are some switches that are not in the switch matrix! This includes the coin door Auto-up/Manual and Advance switches, and the six switches for the special solenoids. The six special solenoid switches include the pop bumpers and slingshot activation trigger switches. These non-switch matrix switch activates the device (like the spoon switch on the pop bumper, or the slingshot switch the ball hits on the playfield). But these devices also have a second switch that *is* in the switch matrix, and handles the scoring for these devices. The second switch is closed as the device energizes, hence telling the CPU to score points for that device.

Using the Built-in Switch Diagnostics and an Alligator Jumper.
At this point I assume the game is basically working (except for some/all of the switches). Because if the game is at least semi-working, the internal game diagnostics can be used to help isolate problems and identify switch problems. The purpose of this test is to find if the switch problem is on the playfield or on the driver board (you must know this to fix the problem).

To access the switch diagnostics:

• Turn the game on and allow it to go into attract mode.
• Press the coin door Auto-up/Manual switch into the manual position.
• Press the coin door Advance button. On system3 to system6, the score displays should go blank. On system7, all the score displays will light up with "0000000".
• Press the coin door Auto-up/Manual switch into the auto-up position.
• System3 to System6 only: Press the coin door Advance button.
• The game should now go into the first test, which is the score display cycle test. All the score displays (including the credit/ball-in-play) should repeat "000000" to "999999".
• System 7 only: Quickly press the Advance button again to pass over the score display test. This will go to test 00, as indicated in the credit score display, which is the sound test. Each sound number will be displayed in the ball-in-play window, and played on the sound card.
• Quickly press the Advance button again to pass over the previous test. This will go to test 01, as indicated in the credit score display, which is the lamp matrix test (all the CPU controlled lamps will cycle on and off at once).
• Quickly press the Advance button again to pass over the lamp test. This will go to test 02, as indicated in the credit score display, which is the solenoid test, and each solenoid from 01 to 22 (as indicated in the ball-in-play display) will be exercised.
• Quickly press the Advance button again to pass over the solenoid test. This will go to test 03, as indicated in the credit score display, which is the switch matrix test. On system3 to system6, the ball-in-play display will show the last read (closed) switch number. On system7 only, if there are multiple switches closed, the switch numbers will alternate in the ball-in-play display.

Any playfield switch can be activiated, and its switch number should show in the ball-in-play display. The game manual or game instruction booklet has a list of the switch numbers, and their associated switch numbers. Also note the flipper relay is activated in the switch test so the flippers will work, and the special solenoids will also work in the switch test.

Now disconnect the driver board connectors at 2J2 (columns) and 2J3 (rows) at the upper right. These are the connectors for the playfield switches. Both connectors are at the upper right of the driver board. Use an aligator test wire and run it from 2J2 pin 1 (col1) and touch the other end of the wire to 2J3 pin 1 (row1). Should see one switch number come on the score display. Then tough the next pin on 2J3. After eight pins on 2J3 are tested (all should report one switch closure on the score display), move the jumper to the next pin on 2J2 (col2) and repeat. Do this for all pin combination (it only takes a couple minutes). If a single pin jump gives more than one switch closure or no switch closure, there is a driver board board.

If all a single switch reports for all pins then the problem is on the playfield. If there is switch column problem at 2J2, it's usually IC17,IC18 (7406). If a switch row (inputs) at 2J3 is a problem, check chips IC15,IC16 (4049). Personally I find the column chips to be more of a problem than the row chips. Beyond that, the driver board PIA IC11 (6821) could also be the problem since it interprets all row and column data. The PIA can be checked with Leon's test chip.

• 2J2 pins 1-3,5 (Columns 5-8 switch drives): IC18 (7406)
• 2J2 pins 9-6 (Columns 1-4 switch drives): IC17 (7406)
• 2J3 pins 1,3-5 (Rows 5-8 switch inputs): IC16 (4049)
• 2J3 pins 9-6 (Rows 1-4 switch inputs): IC15 (4049)

Remember that on connectors 2J2 and 2J3 that pin1 is column or row8, and pin 9 is column or row1 (kind of opposite what you might expect). Also check the manual for the maximum switch number used in the game. Some games don't use any switch numbers past a certain number, and these upper number switches may not report in the switch test.

Strange Switch Behavior.
A user reported a problem on his Firepower when the ball was locked in the left kickout hole switch #13, no other switches in that column #2 with a higher switch row number would work (#14,15,16). If the ball was *not* locked, all the switches in that column worked fine. All the switch diodes were checked for shorts or breaks. Running a switch test as described above with an alligator clip and diode across the driver board connectors showed no problems either. The problem turned out to be one of the two 4049 switch row chips at IC16, for switch inputs rows 5-8. Replacing this chip fixed the problem.

Switch Numbers.
There are some consistent switch numbers from game to game in the system3 to system7 game series. This includes all the switches in column one (switch numbers 1 to 8), which included the coin switches, start button, high score reset, slam and tilts.

Column/ Row	Col. 1 Grn-Brn 2J2-9	Col. 2 Grn-Red 2J2-8	Col. 3 Grn-Orn 2J2-7	Col. 4 Grn-Yel 2J2-6	Col. 5 Grn-Blk 2J2-5	Col. 6 Grn-Blu 2J2-3	Col. 7 Grn-Vio 2J2-2	Col. 8 Grn-Gry 2J2-1
Row 1 Wht-Brn 2J3-9	Sw# 1 Plumb Bob Tilt	Sw# 9	Sw# 17	Sw# 25	Sw# 33	Sw# 41	Sw# 49	Sw# 57
Row 2 Wht-Red 2J3-8	Sw# 2 Ball Roll Tilt	Sw# 10	Sw# 18	Sw# 26	Sw# 34	Sw# 42	Sw# 50	Sw# 58
Row 3 Wht-Orn 2J3-7	Sw# 3 Start Button	Sw# 11	Sw# 19	Sw# 27	Sw# 35	Sw# 43	Sw# 51	Sw# 59
Row 4 Wht-Yel 2J3-6	Sw# 4 Right Coin Switch	Sw# 12	Sw# 20	Sw# 28	Sw# 36	Sw# 44	Sw# 52	Sw# 60
Row 5 Wht-Grn 2J3-5	Sw# 5 Center Coin Switch	Sw# 13	Sw# 21	Sw# 29	Sw# 37	Sw# 45	Sw# 53	Sw# 61
Row 6 Wht-Blu 2J3-4	Sw# 6 Left Coin Switch	Sw# 14	Sw# 22	Sw# 30	Sw# 38	Sw# 46	Sw# 54	Sw# 62
Row 7 Wht-Vio 2J3-3	Sw# 7 Slam Tilt	Sw# 15	Sw# 23	Sw# 31	Sw# 39	Sw# 47	Sw# 55	Sw# 63
Row 8 Wht-Gry 2J3-1	Sw# 8 Hi-Score Reset	Sw# 16	Sw# 24	Sw# 32	Sw# 40	Sw# 48	Sw# 56	Sw# 64

System3 to System6 Driver Board Switch Matrix Jumper Upgrade.
It's a good idea to upgrade System3 to System6 driver boards to be upward and downward compatible from System7 to System3. To do this, replace the 1000 ohm (system3) or 330 ohm (system 4-6) resistors R204-R211 in the upper right hand corner with zero ohm jumpers. System7 driver boards already have this modification done.

The decrease in these switch matrix resistor ohms was done to increase the current drive through the switch matrix. For example, if a switch or connector was dirty and had slight resistance, the switch could still be sensed by the CPU/Driver board.

There is a rumor that using a jumpered system7 style driver board in a System6 or earlier game may result in random switch closures during game play. This does not seem to be the case (but keep it in mind if having random switch closure problems). One thing for sure though is using a non-jumperd System3 to system6 driver board game in a System7 game will definately result in switch closures being missed.

An incorrectly assembled factory switch on a Firepower. The short (top) leaf's gold plated contact is *not* facing the long leaf's gold contact (it is reversed!) So instead of nice smooth gold-on-gold contacts, there is one nice gold contact and a gnarley rivet making contact.

Incorrectly Assembled Factory Switches.
Part of the problem Williams was having with switches was due to an assembly mistake, which started in the mid-1970s (pre-solidstate). It turns out Williams was assembling one of the pair of leaf blades backwards. This was not a huge deal with Electro-Mechanical (EM) games, but with solidstate games, it was a BIG problem. Because solidstate games use low voltage (5 volt) switches (unlike EM games in which all switches were high voltage 28 volts), the contact rivets are gold plated to help keep them clean (gold is a non-corrosive metal). But because one of the switch blades was reversed, a gold plated switch rivet made contact with a gnarley rough non-gold plated switch rivt.

Problems occurred mainly with any switch where a ball "sat", like the ball trough, lock or kickout holes. This mistake was not realized until the Firepower era, and Williams offered retrofit kits for Firepower and Black Knight ball troughs using microswitches to fix the problem. Note an improperly assembled leaf switch can be taken apart, spliting the bakelit "switch stack", and turning around the incorrectly assembled leaf blade.

One or Two Switches Do Not Work (Switch Cleaning).
If just one or two switches do not work, first clean the switch before doing anything else. Most switches on system3 to system7 games are gold contact leaf style switches. These switches should ONLY be cleaned by dragging a business card through their closed blades one to three times, to remove dirt from the contacts. The switch matrix switches are low voltage switches, so the business card trick works great to clean them. Do NOT use a file, as this will remove the gold plating on the contacts, making them way less reliable. The only switches that should be filed are the high voltage flipper cabinet switches and the flipper EOS (End Of Stroke) switches.

Also note on games Black Knight and prior if the switch in question was mis-assembled from the factory (this was mentioned above). Williams mis-assembled these gold leaf switches so one blade was reversed, allowing a gold plated switch rivet to make contact with a gnarley rough non-gold plated switch rivet. These switches can be taken apart and split at the bakelit spacers, and the leaf blade reversed. This was especially a problem on switches where a ball "sat", like the ball trough, lock or kick-out holes.

Another classic problem when one or two or even four switches do not work is breaking of the "daisy chain". Each switch row and column is daisy chained from switch to switch. That is, a switch in column1 row1 daisy chains the column wire to a switch in column1 row2, and so on until the last switch in the chain (usually in column1 row8). If the chain breaks "up stream" (say at column1 row5), all the switches "down stream" (column1 row6 to row8) will not work! So keep this in mind.

Some Switches are Stuck On or Refuse to Work.
If some switches (or an entire row or column of switches) is stuck on or refuses to work, the next thing to determine is whether the problem is on the driver board or on the playfield. The easiest way to determine this is to put the game into switch test, and then remove driver board connectors 2J2 (switch columns/drive) and 2J3 (switch rows/inputs). If the switch problem clears up when these two connectors are removed, the problem is on the playfield (a shorted switch) and not in the driver board.

Also keep in the mind the male Molex header pins or the connnector themselves on the driver board at 2J2 (switch columns) and 2J3 (switch row) could be the problem. Resoldering the driver board's male header pins is a good thing to try if some switch row/columns just won't work.

A Firepower leaf switch showing the wiring of the row and column wires, and the 1N4004 diode.

Row/Column Problem on the Playfield.
If the row or column problem is isolated to the playfield, there are few things to look for in solving this problem. First look for for a short to ground on any playfield switch. A solder splash or a crushed wire between the playfield and cabinet are very common.

Next look to see that all the switches in the row/column are wired correctly (for example, is the diode reversed?) A reversed switch diode will cause all sorts of switch matrix havoc, such as phantom switch closures and row/column shorts and confusion.

Another classic problem where an entire row or column does not work is wires pulling out from the square male/female connector housings, especially where the playfield plugs into the wiring harness.

Lastly look at the diode itself and make sure it is not shorted or open. Playfield diodes (1N4004) can be tested with a DMM set to the diode function:

• Turn the game off.
• Unsolder or cut one end of the diode from the switch.
• Use a DMM set to the diode function.
• Put the black DMM lead on the banded side of the diode.
• Put the red DMM lead on the NON-banded side of the diode.
• .4 to .6 volts should be seen.
• Reverse the DMM leads, and a null reading should be seen.
• If these values are not seen, replace the diode with a new 1N4004 diode.

Problem On the Driver Board.
There are several culprits to examine on the driver board. If a switch column (drive) is stuck on, chips IC17,IC18 (7406) could be at fault. If a switch row (inputs) is stuck on, chips IC15,IC16 (4049) may be the problem. Beyond that, the driver board PIA IC11 (6821) could also be the problem.

Using a Logic Probe to Test the Switch Matrix.
This can be diagnosed further using a logic probe. Remove connector 2J2 (switch columns). With the game on and in switch matrix test mode or even just attract mode, put the logic probe on each pin of connector 2J2. The logic probe should be pulsing for each pin. This is the driver board scanning the switch matrix columns. If a pin is high or low and not pulsing, then the associated 7406 chip or PIA is probably the problem.

To test the switch rows, first make sure driver board connectors 2J2 (switch columns) and 2J3 (rows) are removed. Turn the game on and probe all the pins of 2J3 (rows). There should be NO activity on the logic probe! If the logic probe is pulsing, a switch row is shorted.

Now replace connector 2J2 (switch column) and connector 2J3 (switch rows). Using a logic probe, touch connector 2J3 pin 9. At the same time, try closing a switch in row 1, like the plumb bob tilt (check the game manual for other switches in row 1). The pin should pulse when a switch in that row closes, and stop pulsing when the switch is open (remember there could be other playfield switches in row 1 closed, so keep that in mind). If a switch in that row is not close, the logic probe will show no signal. Note some games don't use row 7 or row 8 of switches, so don't bother testing those.

Also note using this same technique, if the logic probe is on connector 2J2 pin 9 (column 1), a continual tone will be heard, but the tone changes as the plumb bob tilt switch closes.

Using Leon's Test Chip for the Switch Matrix.
Leon's test chip (as documented in the Dead CPU section) can also be very helpful for diagnosing driver board switch matrix problems. The "tester LED", as decribed in the Dead CPU section, and Leon's test EPROM are needed for this.

First, remove fuses F2 and F3 from the power supply before proceeding. This removes the voltage to the lamp matrix and all the solenoids. Also remove driver board connectors 2J2 and 2J3 (switch matrix plugs). Then install Leon's test EPROM into CPU socket IC17 (as described in the Dead CPU section), and turn the game on.

When using Leon's test chip to test the IC11 switch matrix chip pins 2-9 on the driver board (switch matrix), a slight modification is needed to the driver board. On driver board connector 2J3, short to ground *all* these connector pins when testing IC11 pins 2-9 (PIA outputs PA0 to PA7). If this is not done, IC11 pins 2-9 will not alternate on and off.

Use the "tester LED" with the non-resistor lead connected to +5 volts (TP9 on system6/7 CPU board or interconnector pin 1 on the far right) and check the PIA chip IC11 (switch matrix) with the resistor end of the tester LED. Check:

• PIA Pins 2-17,19,39 high then low, alternating on and off every second.
• PIA Pins 26 to 33 are the data lines, and should be pulsing (use a logic probe for this).
• PIA Pin 34 (reset) should be high.

If any pin 2-17 are not alternating high then low, then the PIA is bad. Remove the bad PIA chip, install a socket and a new PIA 6821 chip.

Leon Testing Switch Matrix "Drive" (Column) Test (2J2).
Again with Leon's test chip running, connect the tester LED's non-resistor lead to +5 volts (TP9 on system6/7 CPU board or interconnector pin 1 on the far right). Using the resistor lead of the tester LED, touch each pin on driver board connector 2J2. The tester LED should alternate on and off, in unison with the blinking LEDs on the CPU board. If the alternating signal is missing on any connector 2J2 pin, yet all the IC11 PIA signals are present, IC17 or IC18 (7406) on the driver board has failed.

To verify which input c