Williams System 3 - 7


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

1 Introduction

Williams entered the SS (Solid State) era with a conversion of a 1976 Williams EM (Electro Mechanical] pinball game called Grand Prix.

It is thought that 4-5 games were converted to solid state prototypes using the new WMS System 1 MPU and digital displays.

Next was a 10 unit run of another 1976 EM game called Aztec. The SS version of Aztec is considered to be WMS System 2 and is also very rare. Both System 1 & 2 happened right at the end of 1976. It was a hybrid machine still retaining the EM chime unit in the cabinet for sound and a credit window and EM numbered reel behind that on the backglass. The player scoring was digital.

System 3 games were the first Williams SS production games, starting with Hot Tip in Nov. '77 and ending with Disco Fever in Aug '78. There were based on the Motorola 6800 8-bit CPU and using a Motorola 6820 PIA (Peripheral Interface Adaptor) to handle the Display I/O from the MPU board. They also had three other 6820 PIAs (the same type) on the Driver Board for the Switch inputs and the Lamp and Solenoid outputs. Solenoid drives were mainly for the Coils at this point, a few triggered sound calls or the 'start of game' tunes.

During System 3 (Phoenix, Disco Fever) a memory protect circuit modification was added as to help protect CMOS RAM data during power up and power down of the game. DIP switches were being used to set game settings (such as # of balls per game, high score replays).

System 4 games ran from Pokerino in Nov '78 through to Stellar Wars in Mar '79. A notable game just before Stellar Wars was Flash (another Steve Ritchie designed game and one that outsold all of the other System 4 games combined with a production run of 19,505. During System 4, Williams moved from using DIP switches to change game settings to having the game settings changed from the coin door switches. The settings were still stored in battery protected CMOS RAM. [ed Note: Citation needed ? - I'm fairly sure this is accurate] A coin door interlock switch enforced that CMOS memory could not be modified unless the coin door had been opened by the operator. Some of the game audits (coins accepted, total number of games played, etc.) still could not be changed without access to the MPU board behind the backglass.

System 6 games ran from Tri-Zone in Jul '79 to Scorpion in Jul '80. Two notable games from this era were from the end of '79 and the beginning of '80 Gorgar and Firepower. Gorgar (14,000 produced) was the first talking pinball, and Firepower (17,410 produced) both talked and introduced the 'Lane Change' and 'Multiball (tm)' features to SS games. Note that there had been Multiball play available in EM games, it just wasn't called Multiball (tm) until Firepower. and this is a common misunderstanding. The features these games introduced became standards for almost all pinball games produced right up until today.

System 6a deserves to be mentioned here as it marked a transition to System 7. The game Alien Poker from Oct '80 used the Syatem 6a MPU board (which was not very different from System 6). But it supported 7 digit scoring displays and a redesigned Master Display Driver board, located behind the backglass on the back of the 'Lamp Board'. It also used a special 4 digit "credit/match" display in the approximate position where the System 6 Master Display Driver had been showing the same information (on a 6 digit display, with 2 of the digits unused). This new 7 digit scoring displays with a 4 digit credit/match display were then used in all the System 7 games (and System 9).

System 7 games ran from Black Knight in Nov '80 through to Star Light in Jun '84. Complete System 7 Game list

Black Knight (13,075 produced) introduced a two level playing field and Magna-Save (tm) where the ball could be stopped from draining down the sides by pressing a cabinet button that activated an electromagnet. Star Light (100 produced) was a 'botique' game by Williams' prduction standards as the focus was then on System 9 and the production line for Space Shuttle (7,000 units). At least one Star Light game was used as the Prototype for System 9.

System 8 was used on a single game Pennant Fever in May '84. This was a 2 player 'Pitch and Bat' game with men running round bases. It was the first solid state 'Pitch and Bat' that Williams produced. System 8 was never used for pinball games.

Further discussion of changes and good pictures of the backbox boards for System 3-7 games can be found here: Tukkan.fliput.net

2 Games

2.1 System 3

Contact
Disco Fever
Hot Tip
Lucky Seven
World Cup

2.2 System 4

Flash (Later run were System 6)
Phoenix
Pokerino
Stellar Wars

2.3 System 6

Blackout
Firepower
Gorgar
Laser Ball
Scorpion
Time Warp
Tri Zone

2.3.1 System 6A

Algar
Alien Poker

2.4 System 7

Barracora
Black Knight (Early models used a System 6 power supply)
Cosmic Gunfight
Defender
Firepower II
Hyperball
Joust
Jungle Lord
Laser Cue
Pharaoh
Solar Fire
Star Light
Time Fantasy
Varkon
Warlok

3 Technical Info

4 System 3-7 Board Set

4.1 System 3 Architecture

System 3 Technical information goes here.

4.2 System 4 Architecture

System 4 Technical information goes here.

4.3 System 6 Architecture

System 6 was an upgrade to the System 4 design, they took advantage of the internal clock in the 6808 CPU, and removed the need for the 6875 clock generator (a companion chip to the 6800 and now obsolete and impossible to find).

This also changed the way the 'watchdog' circuit functioned. The watchdog monitors the CPU (IRQ signal), and will blank the displays and lamps as well as stopping the solenoids from firing. When something goes wrong, perhaps the MPU board has locked up, 'blanking' should prevent further damage to the game by 'locked on' coils and other output components driven from PIAs on the MPU/Driver boards.

More ROM memory could be addressed, and this was used to hold increased game code. As an example, Firepower used a 2716 2K Game ROM (which was standard for IC14) plus 3 x Harris Bipolar Proms (512 bytes each) giving a total game code size of 3,584 bytes. Having just 3K of code space is nothing by today's standards. Programmers had to work hard to get good game code in such a small space.

During early System 6 revisions the transceiver chips, 8T28 ICs at IC9 and IC10 were found to not be needed. They were eliminated from the design, as they didn't need to amplify signals to and from the Data bus with modern ROMs. If the ICs are working, then leave them alone. But if not, these buffers are obsolete and can be removed and bypassed, in effect by jumpering the Data Bus pins of the CPU directly to the Data Bus. On Firepower alone you must do the 'Combo ROM' modification, to allow the use of a 2732 Eprom as the Game ROM at IC14. This replaces the Firepower game code found in 4 ROMs as described above, and is an excellent idea. Less chips to worry about, less sockets to replace. All other System 3-6 games will use one 2716 2K Game ROM (or Eprom) in IC14.

Williams also moved to using the updated 6821 PIAs and the 6802 CPU during System 6. [ed note: A citation is needed for exactly when this happened, perhaps with verification from an original owner's game board?]

The 6802 processor was the same architecture and "backwards compatible" with the 6808, but had internal RAM, instead of the 128 x 8 bit MC6810 which must be used with the 6808 CPU. Pin 36 is usually grounded on the 6808, and you can therefore use a 6802 on older boards and it will work, provided the external 6810 RAM is good. If you set Pin 36 of the 6802 "high" (usually through a 4.7K "pull up" resistor to the +5v logic rail) then the internal RAM is enabled. The 6810 (if not socketed) can usually be left in place.

4.4 System 7 Architecture

System 7 was considered a major step change. It had a redesigned MPU board, now supporting a single 7-segment LED display for indicating improved diagnostic information, instead of the original 2 LEDs that System 3-6a MPU boards had used. It also added commas to the player scoring displays and moved the sound select support to the MPU board. An extra 6821 PIA supported both the sound/speech selects and the display of commas. An extra 12-pin header at 1J8 was added to provide connections for the new Sound and Commas support. This freed up five solenoid drives at positions #9-13 on the Driver board, which had been sound/speech selects. They were then available to drive extra game Coils or Flash Lamps.

The MPU used two 2114 Static RAMs, these 1024 x 4 bit RAMs replaced the use of 6810 RAMs mentioned above. There was extended memory addressing, support for multiple 2732 ROMs (or EPROMS) as standard and a huge number of jumper selections available. The jumpers support various memory addressing schemes and ROM sizes, making the System 7 board MPU "backwards compatible" and able to emulateany of the previous System 4-6a games. Provided, of course the correct Jumper Settings and EPROMS are installed.

The Sound and Speech boards were unchanged for System 7, both sound and speech boards remained compatible from their introduced for Gorgar. In some cases the System 7 game had no 0.100" 40-way IDC header for the speech board connection, as this was a cost saving measure made by WMS for games produced without speech. This connector is cheap and available today, as it is still used for PC IDE hard drives, and modern PCB connections. Adding this connector back to the sound board allows it to support a speech 'daughter board' by removing the Jumper at W1.

The separate Driver Board remained almost completely unchanged from System 3 right through to System 7. One small change was made to the Driver Board during System 7. Eight resistors were changed to zero-ohm jumpers in the switch matrix inputs, apparently to increase sensitivity.

The Driver Board mates with the MPU board using 40 x 0.156" header pins on the MPU and female sockets on the Driver Board. This is a continual source of repair problems for this era of Williams machines. To solve this, when designing System 9 Williams combined the MPU and Driver Boards (and the Sound Board) on to a single PCB (Printed Circuit Board), and removed the problems associated with the now infamous Williams "40-way" connector. Only the speech board remained separate, as digital speech was considered an optional feature.

4.5 Flipper ROMs

The OS (Operating System) for a Williams pinball game is called the Flipper ROM. Flipper ROMs with the same color label can be considered generic, although there is at least one exception where a 'custom' White Flipper ROM was used World Cup Soccer.

The Game ROM can be considered the 'personality' ROM, it provides the rules and objectives that are specific to that game's playfield layout. It also maps the Lamps, Solenoid and Switch Matrix to their specific purpose for that game and controls how they are sequenced and timed. Examples would be the 'attract mode' lamp sequence or when sound / speech select calls are made.

Because of the large game production runs, Williams bought batches of Masked ROMs (fixed and not erasable) for the games. This was cheaper at the time than using Eproms (UV erasable, with a small window) as Eproms were still fairly expensive in the 80's. They used the same method for producing most of their Flipper, Game and Sound ROMs.

You may want to replace Masked ROMs with Eproms of the correct type as the original ROMs are 30+ years old. As the legs blacken and tarnish they will weaken and fall off. For a similar reason, many of the ROM sockets on the MPU boards will need to be replaced, especially any sockets bearing the words 'Scanbe', which are poor quality. Masked ROMs are very stable as they start life as all 1's and then the information is programmed by "burning" each selected bit open, like blowing a tiny fuse. So they will rarely will lose their programming over time. If you ever wonder about why we 'burn' our CDs and Eproms, that may be the source of the term.

4.5.1 Flipper ROM Colors

Williams used standard ROM files for System 3-7. These two Flipper ROMs are located at IC17 and IC20. Systems 3-6 use two 2716 or 2316 Eproms, while system 7 used a 2716 in IC20 and a 2532 in IC17.

4.5.2 White Flipper ROMs

Mainly for System 3 games.

4.5.2.1 Exceptions

Pokerino (Nov '78) and Phoenix (Jan '79): Both System 4 games, but use standard White Flipper ROMS. World Cup Soccer: Uses White Flipper ROMs, but the ROM in IC17 is unique - the MPU will not boot and run with the standard White ROM.

4.5.3 Yellow Flipper ROMs

Used in System 4 games.

4.5.3.1 Exceptions

Flash (Jan '79): Earlier version used Yellow, a later version used Green Flipper ROMs (Green is preferred). As always, the Game ROM used must match the Flipper ROM color that it was written for.

4.5.4 Green Flipper ROMs

Used in System 6 / 6a games. Tri Zone (Jul '79) to Alien Poker (Oct '80)

4.5.5 Blue Flipper ROMs

Used in System 7 games. Black Knight (Dec '80) and later.

4.5.5.1 Exceptions

Star Light (June '84, 100 produced) which was the last System 7, appears to have non-standard Blue Flipper ROMs. For very small production runs, games were supplied from the factory with Eproms. Both my Flipper ROMs 1 & 2 are not standard Blue ROMs (checksums differ).

5 Problems and Fixes

5.1 Wiring Connector Issues

Williams made a poor wiring harness decision with this series of games that will allow you to incorrectly connect the cabinet harness to the head harness. Always be sure to double check not just connector pin counts and colors, but most importantly, wire colors. Not mating these connectors correctly will allow the 28V solenoid circuit to fry the 5V logic circuit and can cause extensive damage.

5.2 System 7 MPU Board Issues

Diagnostics, and 'my System 7 MPU Board won't boot'.

Forget about getting anything at all on the Player Displays without having working ROMs in place and a good MPU board. Blanking has to go 'high' before the displays will work. So coin door game diagnostics are useless until the MPU board runs correctly.

But help is at hand on the System 7 MPU, Williams added a single 7 segment LED display to the board To get anything at all on the 7 segment display LED on the MPU you need: The 74LS47 Display Driver IC34 to be working. The 6821 PIA (at IC18) on the MPU responsible for driving the score displays to be working. The logic +5v to be good.

Normally when a working board boots, the LED flashes "0" briefly and the OS turns off the LED display. The game, if attached would then be in attract mode if everything was perfect. Pressing diagnostics should show a "0" and then return to attract mode with the LED display blank. [ed Note: Correct me if that is wrong]

Once you have that the above chips installed and working and sockets replaced or tested good: With no ROMs installed, a board with a fault or a ROM fault if they are installed, the "top two" LEDs (if there) would be lit and the LED dislpay would show "0". The MPU board is 'locked up', in that condition. Display Driver PIA IC PA4 - PA7 will be high. Pressing the Diagnostic switch will not change things.

Then you need an OS, which is the 'Flipper Roms' in pinball. When they 'Boot' (provide a set of instructions to the CPU)- even with the Game ROM removed, the fist thing they do is to "turn off" the LEDs 1+2 and so the onboard LED display (7447) would then go blank.

In fact, you should see "0" flash once and go blank. That means the board is not locked and at least Booted the OS.

Anding in a good Game ROM after that may get you to the point of running diagnostics. Pressing the diagnostic switch would then provide a (hopefully) valid indication of what component is stopping the (pinball or whatever) from running. Here are the key indications (for System 7, SYs 8&9 may be similar):

You can get these results with error conditions by using your Flipper and Game ROMs, or the 2532 WMS Test ROM in IC17 (on Sys 7 boards): If all the support chips are good, and you can get one "0" flash and then it goes blank, then you can trust the on-board display,

Press the diagnostic button, the numbers are:

System 7 LED Diagnostics
Number	Meaning
0	Test Passed
1	IC13 RAM Faulty
2	IC16 RAM Faulty
3	IC17 ROM 2 Faulty
4	IC17 ROM 2 Faulty
5	IC20 ROM I Faulty
6	IC14 Game ROM 1 Faulty
7	IC26 Game ROM 0 Faulty
8	IC19 CMOS RAM or memory protect circuit faulty
9	Coin-door closed, memory protect circuit faulty, or IC19 CMOS RAM Faulty.

Getting an 8 or 9 is *good* to see - you're almost there! Here are some further tips about those conditions:

8 - MPU board may be good. Is it looking for the Driver board? Make sure it's there and the "40-way" interconnect is perfect. Test again. The interconnect isn't there for System 8 onwards... by System 9 MPU and Driverboard (and Sound!) are all one PCB.

Then suspect that IC19 RAM is faulty or finally a memory protect fault.

9 - First check for coin door closed (or pin 1J4-1 or 1J3-1 is being grounded), then is IC7 faulty? Finally is IC19 RAM faulty?

If you get a "9" - I'm always tempted to install in a game open the coin door and try and boot up. But this is wrong, as you still have something not right. Your IC19 5101 CMOS Ram is faulty, or another memory protect component is faulty.

Remember to do the "switch on, off and back on again quick" trick to see if you can get attract mode when reinstalling in a game after taking an MPU out. That's a classic Fonzarelli move, a "golden oldie" of the pinball world. Because lots of times that does the trick.

Parts: The 7-Segment display can be replaced with a KINGBRIGHT SA03-12HDB LED 0.3" RED DISPLAY. 5101 CMOS RAM. 5101-1 The low power version is needed, as it needs battery backup to hold RAM contents when the game is powered off. A 6821 PIA is a standard part. MC6821 MC68B21 are common. xx6821, xx68A21, xx68B21, where xx can be MC (Motorola) or HD (Hitachi Data) will all work. I forget what A means without looking it up in a datasheet, the B means up to a 2Mhz clock, without any letter to 1MHz.

5.3 Reset Issues

5.3.1 Voltages

The MPU board needs two voltages to boot: +12v which only the MPU uses for the reset circuit, and +5v (logic power) for the MPU and Driverboard IC chips.

If the game goes dead, but the sound board continues to work then you may have a fault with the PSU, power connections to the MPU, blanking or the reset circuit.

You check for sounds by pressing the sound board diagnostic test. You need to switch off & back on to cancel the looping sound test. The sound board has its own PSU. It takes 18v AC directly from the transformer and makes +12v (reset) +5v ( logic) and also -12v (Speech and mixers). It's probably OK to assume the +5v and +12v going to the MPU (and Driver Board) are OK from the PSU if the sound board boots and runs. it's like a mini MPU, with the same CPU and one PIA chip.

The main PSU board only needs to make the first two, +12v and +5v (no -12v) for the MPU and Driverboard. But it also generates DC power for the flippers and the solenoids (+28v DC or so).

5.3.2 Connectors, connectors and connectors

With this era of game, most of them 30+ years old now, you will have problems with connectors. If your game starts to reset for no reason during play, it may be worth first re-pinning the connectors at 1J2 on the MPU Board and at the outputs from the PSU. This is always a good step, even it it does not fix the immediate issue. It avoids power problems later on.

This involves replacing the header pins on the board and the female connectors on the cables. The pins are .156" (and I prefer square pins) although round are still available, phosphor bronze. On the female side, crimp pins of the trifuricon type are best. Second prize goes to just replacing the female IDC connectors with new ones. But in that case rather than a crimper, you must buy a .156" 'punch-down' tool, which is a specific part for this replacement to work correctly. Don't buy the tool, and you will damage the IDC housing and pins, and the wires just don't seat correctly.

Again, the connector is a .156" 9-way connector at 1J2. There is also a 'key' pin where the hole is blanked off on the connectors and the pin cut off flush with the board. This prevents plugging the power in to say the switch matrix or swapping two connectors over. It's easiest to just buy a bag of these for blanking off the 'key' positions, rather than try to re-use old ones.

5.3.3 The Reset Circuit Explained

That +12v for reset goes into a circuit that waits (for about a 1 sec. delay) for the +5v to stabilize before it lets the CPU boot. If the +12v (or output from the reset circuit) drops, the reset halts the CPU, PIA(s) and the 5101 CMOS RAM chips before the +5v to them dies. A shutdown of the CPU will also pull blanking low and halts solenoids, lamps and displays to protect them from further damage (coils firing, memory glitching) during the power down. So spikes or drops to the +12v line may halt the CPU at the wrong time.

An MPU unable to boot may mean that its reset circuit is faulty. A +12v line comes in from the PSU board to the MPU on pin 9 of 1J2. That's the top pin, you can also measure the +12v at TP1 on a System 7 MPU. Don’t get hung up on it being exactly +12v, it's not that regulated, but it can’t drop too much lower than 11.5v or the reset circuit may have a problem generating enough voltage to keep reset “up” to the CPU. But 11.5v to 14v is not unusual and can still work. A fluctuating reset that can cause the game to reboot during a game.

You can measure reset’s condition at TP8. That’s the far right test point on the bottom of the MPU just above the 40-way connector. Should be marked as TP8 on the PCB mask. When booting the game and watching reset, it stays low for a heartbeat after power on and then hit +5v. 4.75v or around that is fine. Don't get hung up too much on the voltages being exact for the reset circuit either.

If we find that the +12v is looking OK when we measure it, and the sound board is always booting and working... I’d believe the +12v at the PSU to be stable.

A good trick to 'inject' a reset, is to try connecting +5v for a second or two to the reset test point at TP8. If the CPU boots (reset must be a logic high now on pin 40 of IC1), then you will need to rebuild the reset circuit on the MPU.

So that involves running a jumper lead from TP8 and briefly touching TP9 (+5v). TP9 is at the top right the battery holder (but you should have removed that old holder and added a 'remote battery' holder), so it's top right of where the original used to be.

5.3.4 Repairing the Reset Circuit 'Divide and Conquer'

Let's assume the game boots and works if the CPU reset pin is held high. How do we figure out what is wrong? One solution is a shotgun method - just start changing transistors and components until it is fixed. A better way is to narrow down the fault location using the 'injection' trick.

The reset circuit is easily seen as two halves. For a System 7 MPU board, you can apply +5v directly to the top of resistor R12. If the board boots and stays stable, you know that the problem is on the 'right hand' side of the circuit. (On System 6, you do the same thing but using R32. In this way you have 1/2 the components to worry about.

Assuming that you know the +12v getting to MPU board is good, if the above injection of 5v doesn't work you measure where the voltage disappears on the left hand side of the reset circuit. Then replace parts on that side, checking for reset becoming good when the board boots each time, if you want to replace the minimum number of components. Remember that for System 6 and 7, there are just 12 active components that make up the reset circuit, and 8 of those are transistors. They are usually the source of the problem.

5.3.5 Step One

The Right Hand Side. Start by replacing transistors Q6 – Q9 (all 2n4401 NPN) get 10 or more of them, they’re cheap to buy and you will need them lots of times. They are used as pre-drivers for the solenoid power transistors on the Driverboards for System 3-7). Test the board for your booting problem. If still there, replace the two zener diodes: ZR1 is a 6.8v Zener (1n5996) and ZR2 is a 3.9v Zener (1n5990) - you can't replace these components with anything else to my knowledge. These are critical values. And put the orientation of the band of the diode the same way as the ones you remove. Taking a digital picture of how the circuit in the top left of the board looked before you started is a good ides. Or replace components one at a time. You could of course test for boot on the bench each time you replace something, that may slow things down but you won't replace too many components you didn't have to. It should be booting now, if not attack the other half.

5.3.6 Step Two

The Left Hand Side. Start by replacing transistor Q2. Q2 is a 2n4403 PNP transistor, cheap as well but you won’t need as many for pinball repairs. then replace Q3-Q5 with the 2n4401 's like before. I would replace D19 (a 1n4148 fast switching diode) you could test it with the diode setting of your DMM, but I don't trust testing diodes in circuit, and if I’m soldering in that section, I just cut it out and replace it. Cost will be pennies, and most pinball people should have new ones on hand. Again, be sure and notice the direction of the band on the old diode, and put the new one back the same way. Same thing goes for the orientation of the flat side of the transistors. Don’t get them wrong when replacing. The last component to replace would be the capacitor at C27 (10 uF @10v is the original part –look on the side of the cap). Replace it with a tantalum 10 uF @ 16v, if you can find it. You can go up in voltage even to 20v or more, but don’t change the value of the capacitance. Note that some caps have markings showing a (-) side, usually running down the side of the capacitor. If it shows a polarity, the (-) side of C27 points down on the PCB, towards the 40-way interconnect.

5.3.7 Step Three, Hopefully Reset is Back Up

That’s it. Usually fixed at step one, and down to one (or more) of those transistors. I have seen a zener or the 1n4148 diode at D19 be the problem before. But for me, the cap C27 has always been good. If all else fails, test the capacitor for a dead short with the power off and replace it with a 10uF electrolytic if it is shorted to ground or you aren't sure it's working.

5.3.8 Kudos and Summary

Thanks goes out to Cody Laux, who owns a game that was resetting (going dead and blanking) when all four flippers were fired. He approached me a question about his out his Black Knight (an excellent Steve Ritchie design). This prompted me to explain the reset circuit repair to him in my own words. I've mentioned connectors above for completeness, which he was already aware of and had replaced. He had also replaced the Bridge Rectifiers and rebuilt the 40-way connector. While I agree a good 40-way connector is essential for correct operation of System 3-7 games, the BR's are only for the Lamps and Solenoids and won't usually fix a problem with the MPU power (or reset) as that is sourced directly from the PSU and +5v regulator board. Cody was dealing with a game reset when flipping, so in his case it made sense to check and rebuild the solenoid power circuit as well.

Here's hoping he fixes his BK, and if so I'll post back a solution here, or move the solution to the correct area. The above step-by-step repair guide of the reset circuit will be no less valid for others to use with MPU problems. This takes us smoothly on to the next section about the PSU Board.

5.4 Power Supply Issues

5.5 Display Driver Board Issues

5.5.1 Repairing the Master Display Driver

Note that the detail here is for System 3 - 6a with 6-digit displays only. So it does not include Alien Poker or Algar, which both used the System 7 type display setup. System 7-9 used a smaller Master Display Board located on the back of the lamp board, and it had IDC type ribbon cables that ran to the 4 player 7-digit displays. They added a 4-digit Credit/Match display which also used a ribbon cable. The harness connecting the backbox (PSU and MPU) signals to the Master board used the same 'edge-connector' as System 3-6).

Firstly, a ***Warning*** With the game on you are dealing with +100 and -100v HV DC (High Voltage) going to the displays. That's a potential 200v difference and you only need to feel that once to know it. Wear tennis shoes (trainers or any rubber soled shoe) when working on Diplays with the backbox open. This is a shock hazard! If you are not capable or happy with measuring these voltages with a steady hand, then get someone else to help you or be there to 'spot' you. Always a good idea and more fun than working on your own.

Sometimes displays go blank and it is in the wiring harness from backbox to the Master display, and not the Display Driver PCB at all. If you can swap a working Master Display driver board from a System 3-6a game with displays that are stable, then do that first. You can quickly determine if the fault is cabing / display PIA on the MPU (so in the backbox) OR the Master Display driver PCB on the front of the light board.

5.5.1.1 Segment failures

Segment failures on a single display could be that display failing. Same issue if just one display is blank. Swap that display with another (power off first) and see if the problem moves with that display. If it moves, it's that display glass or its board. If it doesn't move and stays at the same player location, see below for the possible suspects.

Segment failures on multiple displays and probable cause:

Players 1 & 2 Segments and master display Segments are out:

BCD inputs are A1 B1 C1 D1 from the MPU board
MC14543 BCD to 7-Seg. Decoder IC5
UDN7180 Display Driver IC9
Resistors R1-R7

Players 3 & 4 Segments

BCD inputs are A2 B2 C2 D2 from the MPU board
MC14543 BCD to 7-Seg. Decoder IC8
UDN7180 Display Driver IC10
Resistors R8-R14

Start out by measuring all the resistors on the master display board with the power off. R1-R14 should be around 10K ohms. Any that are not within about 10% (say a range between 9.6K to 10.4K ohms) need to be replaced. Also look and see if any look "toasted".

Those resistors get cooked on the Master display boards and usually will then cause single segments to fail on both the player 1&2 or 3&4 displays together, as they are linked. Te resistors need to be replaced with the same value: 10K but at 1/2 Watt. Some of the modern 'metal film' resistors are rated at 0.6W which is perfect and they fit nicely in that location. Older 0.5W (1/2W) resistors are larger, but are fine. Mount them slightly off the PCB so they get good airflow all around the resistor body.

Do the above steps anyway, no matter what the display problem is although it's probably not going to be the whole story. Replacement resistors are cheap and will prolong the life of your displays. Reducing the voltage going to the displays when rebuilding the HV section of the PSU is a good step to take and will help as well. You only need to replace two Zener diodes to achieve this.

5.5.1.2 Digit Failures

Strobe inputs for the display digits come in to three 14069 hex inverters on the driver board. IC1, IC2 and IC3.

IC1 is dedicated to the Master Display 'Credit/Match'. Strobes are: 15,16,7,8 left to right, for the 4 digits it uses.
IC2 and IC3 strobe inputs are more complicated, to strobe distribution between these IC chips is shown in the display diagram below.

Strobe (or strobe input) failures are likely to show up in the player display pairings 1&3 or 2&4 because:

Strobes 1-6 are shared for players 1 & 3
Strobes 9-14 are shared for players 2 & 4

5.5.1.3 All Displays are Blank

This could be that the +100v or the -100v HV are missing from the PSU board. Both have to be there, so check that the output from the PSU and that the voltages (HV) are good first, and getting to the Master display driver to be relayed to the player displays.

There are also 5 x 3 Mega ohm resistors, at R15-R19, These are for the cathode "keep alives" and again should be near that value. If the 3 Meg resistors don't look cooked and are within spec, check that you can see an "orange glow" in the displays when the lights in the room are dim or off. If you see a faint glow (some describe it as an 'orange neon dot'), then look elsewhere for the fault.

If you don't see the display glow, check the wiring to the connectors carefully looking for a burnt wire at pins 4J7-1 -2 and -6 on the master display. Do this with the power off, as you are dealing with 100v and -100v DC. If you find a cooked wire, sometimes just cutting the wire back a bit to expose clean metal and then reinserting it firmly in the IDC connector will repair the problem with a bad connection for one of the HV lines. Remove and reseat all the edge connectors on the master display board and especially examine the ones that go to the backbox. You can clean the copper contacts on the edge connectors gently with an eraser to shine up the copper if it's dull or has "dead spots" worn on it. Check any inline connectors as well.

I also recommend disconnecting all the player displays 1-4 at the Master display. Get it working with the just the credit/match and then with one other display attached, like player 1. Then add back the player 2-4 displays one at a time (you need to power off each time you add or swap a display), tesing for correct function each time. You can also swap the player displays as a diagnostic step and carefully observe if the fault(s) stay with the Display in question or move to the new location. Use the "display test" on the diagnostics for this. After the above is checked, perhaps you do have to suspect the IC chips (or for the discrete version the transistors). Depending on whether the Segments or Digits are out, it will point you at a specific IC (or transistor array). Knowing which displays are out helps reduce the fault domain down to one chip. You need be like a detective, following the clues. Having a Master Display Assembly drawing and a schematic on hand will help with this process.

Here's hoping that it isn't one of the UDN6118A-1 (aka UDN6184-5) IC chips that's faulty. Hard to remove from another board in one piece, without a de-soldering station and becoming obsolete.

5.5.2 Master Display Drivers for System 3 to 6

Master Display Driver Boards came in two versions, discrete and IC based. Williams designed the discrete version when the UDN7180 / UDN6184 Gas Plasma Display Driver ICs became scarce (and they were expensive even then). There are some logic chips that decode the BCD data for the 7 display segments (MC15453 or MC15458) and to buffer and invert the display strobe lines for the digits (MC14069). These buffers and decoders are common to both the D8000 and D8168 versions.

5.5.2.1 Discrete version Display Driver

Williams System 3-6 Master Display Board (Discrete Components)

The D8168 board uses MPSA92 (PNP in a TO-92 package) and MPSA42 (NPN also TO-92) transistors to drive the Master (Credit/ Match) and player scoring displays. These gas plasma display driver transistors are available today and still very cheap to buy. Unfortunately, this style of board is less common to find in the wild, but actually easier to maintain. At least no one can try to charge you $20+ for an obsolete driver IC.

5.5.2.2 IC version Display Driver

Williams System 3-6 Master Display Board

The D8000 IC version board is composed of ICs that implement the transistor arrays. Usual factory chips are the UDN-7180 for the Segment Driver and the UDN6118a-1 for the Digit Driver. You may find the Digit Driver IC is a UDN6184-5 as well from WIlliams.

UDN-7180 IC chips are still fairly easy to find. Cost should be reasonable, if you shop / ask around.

The UDN6118a (Sprague) or uPA6118c may still be available for $3-5 but have a lower breakdown voltage (~85v DC) than original part. The displays run at +/-100v DC as standard and need the higher rated original part which is the the UDN6118A-1 (note we have -1 at the end). The UDN6118a-1 is rare and also becoming very expensive, as much as $20+ for an IC chip.

If you do find the lover rated UDN6118a (or uPA6118c), then you need to replace two zener diodes on the PSU to lower the display voltage down from 100v. It's a good idea anyway on a working System 3-7 game. Not overdriving display glass and less stress on the expensive display driver chips will lengthen the life of your game. Arcades sometimes had bright lights or windows, while in your home you won't notice any difference running at a lower voltage.

I usually drop the voltage down leaving the Power Supply to about +/- 90v with 2 x 1n4763a 91v zeners, at Z2 /Z4. This seems to work, but you are still probably driving near the limits of the replacecment UDN6118a. Unlike the Bally games of the same era, there is no fine adjustment on the HV section of the PSU.

See the Power Supply repair section for more information about parts and upgrades.

Remember to compare the costs and trouble of repairs with buying a replacement Master Display Driver board:

If all that is wrong with the Master is that the Credit/Match display is out, but it drives all player displays correctly, in my experience the repair is easier than on the player display parts of the driver board:

Carefully placing a new 6-digit glass against the pins of the non-working display will confirm if it is the display glass or an IC chip that has failed. Be Careful of the HV (High Voltages) when doing this, and only hold it by the display glass as it is a natural insulator! It takes a steady hand and some practice, but this test will work on other player displays as well. This usually proves the old display has a digit/segment missing, is 'out gassed' or is just prone to flickering. This isn't foolproof, it works works provided the existing display doesn't have a short. If both displays exhibit the fault, cutting the correct 'leg' or legs in the middle on the old display may help reveal this, and you can bend it back and solder back together if it's not shorted.
- You replace the Master display glass with a standard 6-digit gas plasma display, you can even use an old (but working) player display.
- You can also replace the Master display with a player display that has a digit fault and would otherwise be unusable! It's possible because the '100,000s' and '100s' digits are not used on the Master [x00x00]. So you can take two faulty components (a non-working Master and non-working player score display) and make a working Master Display Driver Board. Pinball repair nirvana.

Once you feel the display glass is good, you can look to the ICs which are dedicated to driving the Master (or Credit/Match) Display:

Start by testing IC1, a 14069 Hex Buffer/Inverter with your logic probe. Run the display digits diagnostic test, with the Auto/Manual switch in the Auto/Up position. The digits on all displays should be counting 0-9. Test the strobe lines are being inverted. The strobe lines and associated pins are in the diagram given below.

When reading this diagram remember that Player 1&3 Score Displays share Strobes 1-6, while Player 2&4 Score Displays share Strobes 9-14. One strobe for each digit. The Master Display has 4 digits only: Strobes 7,8,15,16. So if the output pin is not the inverse of the input pin or a signal is missing, then replace IC1. It's available as a 4049U or MC14049UB. Cost is maybe 50 cents, certainly < $1 even in low numbers.

Digit failures will show up in these pairings if they are related to the strobes (so digit drivers):

Strobes 1-6: shared for players 1 & 3
Strobes 9-14: shared for players 2 & 4
The Diagram below is the same for all games, as are the Master Displays which makes them interchangable:
The Table / Diagram is listed in the most obvious order: Master, Player 1,2,3,4 displays.

If that doesn't fix it, move on to the Segment Drivers:

- Look at IC4, the UDN6118A, follow the steps to do a DMM test of the UDN chip. A trick here can be that all the pins are not used (because of the missing digits, so it is possible to make use of the original UDN6118-A-1 (or UDN6184-5) that has a previous fault and one I/O pair is faulty.

This works for the Master Display, so I would keeep a faulty UDN chips (or a faulty board) for spares. You never know (e.g. there is an extra unused pair on every UDN7180 type chip pins 1+18 when we get to Segment driver tricks!!! This does not work when you get to for System 7-9 Masters, as all the pins are used.

Pairs that are needed for IC4 are: 1+18 3+16 5+14 7+12. So you can get away without pairs: 2+17 4+15 6+13 8+11 so you can have up to 1/2 the chip faulty, but it needs to be the right positions without using wire jumpers.

There is a way to test the UDN6118's with the power off and you DMM (multimeter) With the game OFF. Remove the power in to the Master Display board, connector 4J7. DMM goes on the Diode test setting (usually a symbol like this: ->| Red lead to ground, I use the ground braid in the backbox, connected by a jump lead (alligator clips each end) Touch black lead to the UDNxxxx pins 2 through 8 You should get .5 to .7 for each pin Touch Black lead on each UDNxxxx pins 11 through 17 No reading is the correct result. A shorted display glass can show up during UDNxxxx 11 through 17 test.

Notes on different board revisions: Williams also used the DI-0512 (Dionics-512) for the Digit Driver IC. I have owned the discrete transistor version, but the Dionics-512 version is even harder to find, and I've not seen one in 7 years of collecting. That's not to say they are not out there. All the troubleshooting instructions above are intended for the UDN type boards, but the Dionics boards work in a similar way, so consult the schematics. You will also need to make sense of the warnings below.

Warnings: These are factory changes, but if you replace or swap chips, you should be aware of the following

The Display board must run similar chips, so for example all UDN-6118 / UDN-6184 types for the Digit Drivers OR all DI-0512 Digit Drivers (which are longer, meaning they have more pins). They have different power requirements! The two Segment Driver ICs need to match, too. So two MC14548 ICs at IC6 & 7, OR two MC14543 ICs at IC5 & 8. Mix & Match or having all four installed is mental (crazy)! You should have empty pads on the board for the optional IC chips.

With the DI-0512 at ICs on these boards, the '10K' resistors R1-R14 are all 15K. Adjust the repair instructions below accordingly.
If IC4 and IC11-14 are UDN-6118 chips, then a +100v trace is cut connecting pin 2 of connector J7 and ZR1 (1N4740A Zener diode) is added.
With the DI-0512's this trace is left, and there is no Z1 used.

I have seen a HV arc occur between two pads on the Master Display board, and this blew out the HV section of the PSU. If you have the UD7180 version of the System 3-6 Master Display board, it may be worthwhile taking this easy step to prevent a problem:

There is an unused track on the front of the board near to the bottom right corner of the Master display glass. The top round pad in this picture is unused on the UDN7180 version but goes to the +100v supply at Pin 2 of 4J7.

It appears that the pad shorted out to the ground track that goes around both of the round pads. Cutting the track to the top round pad as shown in the picture (with the board removed from the game) will cause no problems for the displays on your game. But it could prevent disaster. A short could damage the HV section of the PSU, even the Master Display board itself. I have seen it happen, so better safe than sorry. BTW- This track should not be cut if the Dionics Digit Driver ICs are installed.

More later - almost done. --Firepower 05:01, 28 April 2011 (BST)

5.6 Sound / Speech Board Issues

The sound board is actually a "mini-MPU" board running a 6808 CPU and 6821 PIA. It has it's own PSU and takes 13v AC voltage directly from the Transformer and rectifies it to provide the +5v logic and +12v reset circuits. I believe this design was for ground isolation and noise reduction.

I have a whole section hosted temporarily here: http://homepage.ntlworld.com/alienpoker/FP-Parts-Snd.html It is discussing the Sound/Speech architecture and repairs for this era of games. It is my own work, but you may use content on this HTML page for the PinWiki.

I looked into converting it to this wiki with a MS word plugin, but had problems with the conversion crashing. If someone more knowledgeable about the 'ways of the Wiki' wants to take a stab at converting it, I will edit it to fit better in this space. The links to my sites (and diagrams) will need to disappear and be replaced by links to IPDB manuals or other places. I don't mind if the facts and information in tables are presented verbatim as they are my designs and invention.

5.7 Switches

A word of warning: Do not ever file or sandpaper gold switches.

The only switches you can file look like the 'points' in a car distributor (tungsten) if you are old enough to remember them. They can arc and will get blackend (or whitened!) and pitted. Once this happens they offer resistance to current and you flippers will seem weaker. You can file two switches, located on the flipper EOS (end-of-stroke) on early games (EM and SS) and the cabinet flipper switches. Later switches on the EOS are low power switches and have gold contacts. If you file switches that are part of the switch matrix, you will ruin them and they will need to be replaced.

Switches vary from game to game, most are standard for WMS System 3-7.

A few of the common switches are listed here:

System 3-7 Switches
Part Number	Common use
SW-1A-118	Spinner Blade switch
SW-1A-124	Rollover Lanes (inlanes/outlanes as well)
SW-1A-130-1	Switch Rightmost on Ball Runway (Ball Locks, with round white nylon piece on leaf end)
SW-1A-136	2nd Ball Runway Switch (typical, depending on game)
SW-1A-137	3rd Ball Runway Switch (typical, depending on game)
SW-1A-138	Shooter Lane Switch
SW-1A-139	Lane Change Switch (can use SW-1A-150, usually stacked to right flipper or right EOS)

These were used throughout the Williams games: Examples are for the above include System 3, System 4 (Flash), System 6(a) (Firepower and Alien Poker), System 7 (Black Knight). Some appear on F-14 Tomcat (’87) and further, even after most Ball Ramp switches had changed over to micro switches. Black knight also used micro switch kits, but Williams provided as a field replacement kit for operators. Drop Targets also had factory micro-switch adapters fitted later to make them more reliable.

Switch Assembly Note: The Williams factory (or more accurately their suppliers) assembled many switches so one of the blades was facing the wrong way. It should have to gold contacts facing each other, where in fact one blade faces so that the rivet it making contact. If you have an intermittent switch, it can be worth the time to de-solder it and remove from the game and then carefully pry the swtich stack apart and reassemble the switch so the gold contacts face toward each other. Keep the exact order of spacers and just reverse the one blade. While there, carefully clean the switch contacts with naptha and a clean cloth. Again, please don't use emery (or files) on these switch points! Once the gold has worn, they form "dead spots" and won't work reliably.

5.7.1 How the Switch Matrix Works

First of all a switch is usually an electro-mechanical device with moving parts. This includes leaf blade switches, tilt switches (where the ring is fixed and the plumb bob is the moving part of the switch) and micro-switches. When a mechanical switch closes the contacts tend to oscillate before coming to rest. It literally 'bounces' several times before remaining closed.

The CPU could see the rapid open/close events as multiple switch closures, so there is usually some 'debounce logic' built into a switch matrix reading programs. The CPU sees a switch closure and then 'checks back' to see if it remained closed as few milliseconds later. If it is closed, the CPU processes the event once, scoring the correct value or in some cases triggering a solenoid to fire.

As an aside, an optical switch (or opto) has no moving parts and so doesn't suffer from switch 'bounce'. It also shouldn't need adjustment or in theory wear out as quickly as say a micro-switch. But an opto needs additional circuits and is not as simple to work on or replace as other switch types. Although you can not see an infrared transmitter with you naked eye, you can look at it with a digital camera. Optos were never used in System 3-7 games, although they were engineered and prototyped just at the end of System 7.

Wiring up every switch separately with multiple wires running to the backbox would be expensive in the amount of wiring and in the number of inputs required to the game's logic. Rather than do that, the engineers designed a switch matrix with 8 column wires and 8 row wires, creating a 'matrix' of 8x8 giving a total of 64 possible switches. Not all of these switch positions are used.

The first column of the switch matrix (COL 1) is dedicated to the same switches on the System 3-7 games. You can check in a manual, but these will be the cabinet tilts, the coin switches which sense coin drops, the credit button (to start a game) and the high score reset which is also in the cabinet (on the coin door).

For the most part other switches will be on the playfield (exceptions could be a lane change or magnasave button/switch).

So how is the switch matrix read by the MPU? It uses the most useful Peripheral I/O device in this pinball era, the Motorola 6821 PIA (earlier this was the MC6820 PIA).

The 6821 is made up of two 8 bit ports, one port is known as 'Port A' and the other 'Port B'. Any of the 16 pins can be configured as inputs or outputs. That's exactly what's needed to drive our Switch Matrix! An 8-way output port B to 'send' (or strobe) down the Columns to the switches, and an 8-way input port A to 'read' the Rows from the switches. The Columns are known commonly as 'Drives' and the Rows are known as 'Returns' for this reason. In a similar way (an 8x8 matrix) another PIA is used for the Lamp Matrix.

The switch matrix PIA is at IC11 on the Driver Board , and also called PIA II. This PIA doesn't drive the switch matrix directly from it's TTL output pins, as there are +5v powered 'pull-up' resistors and 4 IC's which act as drivers/buffers helping to protect the PIA from damage if the switch matrix is shorted.

Two 7406 (Hex Inverter / Buffer with open collector HV outputs) is used to 'drive' the Columns.: A 7406 or 74LS06 will work and are common parts.
Two 4049 (or 14049 "CMOS Hex Inverter / Buffer) is used to 'read' the Rows.: The MC14049 or CD4049UBCN are common examples, although any 14049 or 4049 14-leg DIP will work.; (Hex in this context refers to six inverters contained in the one IC package. It's nothing to do with the computer (or math) Hex meaning of 'base 16'.

The CPU writes to the output port of the PIA driving column 1, and then 'looks' at each of the rows 1-8 in quick succession. It checks to see if the signal is getting through on the row that's currently being read. Think of it as an 8 bit answer for that column showing which switches in that column are closed. Say 00010001 returned would mean switches at C1,R4 and C1,R8 are closed.

So for every 'drive' down a column, the machine does 8 'reads' of the rows. Then the CPU moves on and drives column 2, looking again at each of the rows 1-8. It continues through all of the remaining columns in this way. This is done very rapidly by the CPU, strobing the whole matrix looping over and over many times a second. Because it's so fast, even multiple switch closures are rarely missed, in fact as mentioned above it has to debounce the results to obtain an accurate result.

The diodes on every switch help to steer the drives only to the row that's being read and not back into other parts of the matrix. That's why good diodes on switches are so important, as they must only allow current to flow in one direction: from column to row. Essentially that's how the switch matrix reads switch closures.

This article by Aeneas describing a later game's switch matrix may be useful as a different explanation with a diagram. Transistors can be used on the drives (as with modern games like DE or Stern ), different buffer chips can be used, but the basic switch matrix design hasn't changed over the years.

Finally a warning about protecting the switch matrix. Please note that nothing will protect the switch matrix IC's and PIA if (for example) the +50v solenoid voltage is shorted into the matrix. This happens if the 'lane change' switch is attached in a stack on the flipper mech and shorted to the EOS switch. In later designs the 'lane change' was moved to be stacked with the flipper buttons (nearly as bad) or to a separate button which was a better design. Be very careful if working under the playfield not to short the solenoid or lamp power into a switch. It can be a lot of work to repair the damage done to the driver board, so be careful with you screwdriver and loose solenoid power wiring. Most people who have been repairing games long enough learned the hard way, and won't work under the playfield with the power on.

5.7.2 Special Switches

There are a few switches that are dedicated, and not part of the switch matrix. The coin door Advance and Auto/Up Manual/Down switches, which let you start diagnostic tests when the switch matrix is faulty. Also 6 special solenoid switches, which directly connect to the solenoid logic on the driver board. When Williams first designed these games, they were worried that the CPU couldn't always 'keep up' with the ball hits to the pop bumpers or slingshots. So during game play the switches on the playfield fire the special solenoids directly from the playfield. These usually include the spoon switches on the pop bumpers and slingshot stand-up switches.

All pop bumpers and slingshots have a second switch which is part of the switch matrix. It closes when the coil is fired and tells the CPU to increment scoring and in some cases to trigger sounds for these devices. The scoring switch is mechanically closed, by the 'elbow' of the slingshot arm or by the armature connected to the pop bumper ring.

Confusingly, the CPU can also fire the 6 special switches from PIA lines for the diagnostic tests, but these PIA signals are never used during game play. If all these solenoids work during diagnostic tests, but not in game play it points to the switch inputs or the 7408s at IC6/7. It won't be the 7402s at IC8/9.

I have seen a game that worked in play perfectly, but the diagnostics could not fire two of the pop bumper solenoids during tests. This was a Switch Matrix PIA with faulty output at pins 19 (CB2) and 39 (CA2), other than that the PIA was working correctly and so it could still be used to drive the Switch Matrix. If a switch row or column went out, the PIA would then have to be replaced.

Here is a list of the PIAs and where the pins are that fire the 'special solenoids' during diagnostics:

Special Solenoid Diag. PIAs
ST#	PIA	CHIP	Pin #	Location / Board
1	III	IC10 Lamps	19	Mid PIA on Driver Board
2	III	IC10 Lamps	39	Mid PIA on Driver Board
3	II	IC11 SW Matrix	19	Left PIA on Driver Board
4	II	IC11 SW Matrix	39	Left PIA on Driver Board
5	IV	IC 5 Solenoids	39	Right PIA on Driver Board
6	I	IC18 Displays	19	Via 1J1-26 on CPU Board

5.8 Testing the Switch Matrix

To test the switch matrix in the game, first remove both Switch Matrix connectors on the top right of the driver board. J2 is Column (green wires) and J3 is Row (white wires). Then run a switch test from diagnostics, you should get no switches being sensed.

Use a jumper test lead with a 1n4001 (or any) diode as follows:

Connect one end of the test lead's alligator clip to the column pin, starting at column 1. That's the bottom pin of J2.
Clip the diode's cathode (banded end) to the other side of the test lead.
Then use the anode (non-banded) side of the diode as a probe to touch to the appropriate row pins.
Start at the bottom pin of J3, which is row 1. You should see switch #1 indicated (R1C1).
Move the probe to the next pin up on J3, which is row #2. You should see switch #2 indicated (R2C1).
When you got to the top of the row pins, move the clip end to COL #2 (up one pin) and start again with row #1.
Activate each switch in turn by connecting the appropriate 2 male pins on the CPU board with your test lead and diode.

Using your switch matrix chart from the manual as a guide, you may find the faults as your game "sees" on the same switches.

If you get an error in sequence, more than one switch registers at a time or you are missing a row or column - then you know the problem must be on the MPU board. You can either try to fix it or send the board out for repair.

If the above test works correctly, meaning all switches register correctly then your problem must be the wiring or on the playfield.

5.8.1 Testing the Switch Matrix PIA

No section on the switch matrix is complete without mentioning the switch PIA. That IC and 4 buffer IC's are the only logic in the switch matrix. Although the complete instructions for testing all the PIAs are beyond the scope of this section.

This is because the only sure-fire way to test the PIA is with the 'Leon Borre test ROM' in the MPU board. You do this by taking the MPU and Driver boards out of the game and putting them on the bench. That will also let you trace back through the circuit to find a fault more easily, and it's not as hard as you may think. It will also exercise the CPU memory and test all the PIAs on the Driver Board, not just the switch matrix PIA. Here are his excellent instructions:

Leon's main site (click on the button for English).

Leon's Repairing MPU Boards including a free test ROM to download for System 3-6 games.

Leon's Repairing Driver Boards

These Belgium guys are knowledgeable about pinball.

5.8.2 Switch Matrix Components

Final thoughts about components which make up the switch matrix.

The passive components: On the driver board there is an RC network, made up of 16 x 4.7K pull-up resistors that you can measure with a DMM. Tolerance is not critical, but should measure between 4.5K to 5K which is about a +/- 5% range. There are also 16 x capacitors (470pF at 50v, ceramic) these should not measure as a short, if in doubt just replace them. And 8 x 1K ohm resistors at the switch inputs (rows) at R196-R203 these can not be open or shorted and must be around 1K each.

You can see the above chips inverting signals with the game running and a logic probe. Check if signals look weak or suspect. If you see a signal on the input side and then nothing inverted on the output side, then that's your problem.

Beyond that IC15-18, which are the Switch Matrix inverting buffer / drivers:
IC Location	Inverting Pairs. Leg a to b listed as a,b	Switch Row/Col Numbers	IC Part Number /Eqivalent
IC15	3,2 7,6 14,15 9,10 in that order	Rows 1-4	(MC)14049U / 4049U
IC16	3,2 7,6 14,15 9,10 in that order	Rows 5-8	(MC)14049U / 4049U
IC17	2,1 6,5 12,13 8,9 in that order	Columns 1-4	7406(S) / 74LS06
IC18	2,1 6,5 12,13 8,9 in that order	Columns 5-8	7406(S) / 74LS06

J2 (Column) and J3 (Row) connector pins:
Connector	Male connector Pins	Switch Row/Col Numbers	IC Location	IC Part Number /Eqivalent
2J2	pins 1-3 and pin 5	Columns 5-8	IC18	7406(S) / 74LS06
2J2	pins 9-6	Columns 1-4	IC17	(MC)14049U / 4049U
2J3	pin 1 and pins 3-5	Rows 5-8	IC16	(MC)14049U / 4049U
2J3	pins 9-6	Rows 1-4	IC15	(MC)14049U / 4049U

Except for the 6821 PIA which is getting harder to find, all the switch matrix components are readily available.

5.8.3 Wire Jumpers on System 7 Driver Boards

Williams removed some resistors from the switch matrix inputs and used wire jumpers instead. This happened from the start of System 7. The first thing to do with a driver board (which may not be from that game) is to measure these resistors and make sure you have the the driver board set up for the correct game. While you may be able to use a board with wire jumpers in System 4-6 games, using a board with resistors in a System 7 game will cause problems. Having the wire jumpers helps with switch sensitivity and helps with sensing more than one switch closed at the same time.

On driver boards from Black Knight and later System 7 games, there should be 8 wire jumpers (or zero ohm resistors) used on the switch matrix at positions W9-W16. These are located on the upper right hand corner of the Driver Board just to the left of J2, the top left connector which is the switch matrix column input. To the left are two columns of 7 resistors, the second column should be the wire jumpers, and also the top position of the next column (column with 2 resistors only).

On System 4-6 Driver boards, certainly through games like Alien Poker, Firepower and earlier SS games there are usually 330 ohm resistors (orange, orange, brown) in the same 8 locations. For black Knight and later (System 7 games) they are called R204-R211, and are zero ohm resistors (usually a tan body with one black stripe) or you can replace or jumper over them with wire leaving teh resistors in place. In all other respects the driver boards are identical, so it's easy to convert between the two. That's why they are usually know as System 3-7 driver boards.

Before you start to replace parts on the driver board, be sure your playfield switches are working and the diodes are good. You need to unsolder one end of the diode from the switch to be able to test it correctly with a DMM on the diode setting. While you are there, clean the switch with a business card soaked in naptha or contact cleaner sprayed on the business card (with the game off, contact cleaner is flammable!. See if any blackness comes off on the card. You can also gently wipe the contacts until shiny with the corner of a clean rag dipped in pure alcohol.

6 Game Specific Problems and Fixes

6.1 Game specific fixes go here

6.2 And here, too

7 Repair Logs

Did you do a repair? Log it here as a possible solution for others.