What Repair Experience Is Expected?
Little experience in fixing pinballs is assumed. Basic electrical knowledge is helpful, but not necessary. I do assume you can solder and use the basic features of a Digital Multi-Meter (DMM) such as measuring voltage and resistance. Please see http://marvin3m.com/begin for details on the basic electronics skills and tools needed. This document should help if you just bought your first (or second, or third) pinball "as-is", and hope to fix it.

Got Schematics?
Having a schematic for your game would be ideal, but sometimes you can fix your game without it. If you don't have a schematic, order one from one of the sources on the suggested parts & repair sources web page. This repair guide is NOT a replacement for the game manual!

Online schematics are available too:

These Schematics thanks to Phil Butcher:

• System 6 (Firepower) Power Wiring Schematics
• System 6 (Firepower) Power Supply Layout
• System 6 (Firepower) Power Supply Schematics
• System 6 (Firepower) CPU Schematics
• System 6 (Firepower) Driver Board Schematics
• System 6 (Firepower) Master Display Schematics
• System 6 (Firepower) Sound Board Schematics
• System 6 (Firepower) Backbox wiring
• System 6 (Firepower) Cabinet wiring
• System 6 (Firepower) Playfield
• System 6 (Firepower) Switch Matrix
• System 6 (Firepower) Lamp Matrix
• System 6 (Firepower) Logic Layout
• System 6 (Firepower) Game Instructions
• System 6 Williams Repair Document

• System3 CPU board Schematic - GIF 150k
• System6 CPU board Schematic - GIF 150k
• System3 Driver board Schematic, part 1 - GIF 150k
• System3 Driver board Schematic, part 2 - GIF 150k
• System3/4 sound board Schematic - GIF 200k

• System6a CPU board Schematic - PDF format, 370k.
• System6a CPU board Assembly Drawing - PDF High Resolution, 3.3meg.
• System6a CPU board Assembly Drawing - PDF Low Resolution, 878k.
• System6a CPU board Bill of Materials - PDF format, 145k.
• Driver Board Assembly Drawing - PDF High Resolution, 5 meg.
• Driver Board Assembly Drawing - PDF Low Resolution, 1 meg.
• System3 Driver Board Schematic, Part 1 - PDF format, approx 280K.
• System3 Driver Board Schematic, Part 2 - PDF format, approx 80K.
• System4-7 Driver board Schematic - PDF format, 8meg
• System7 Schematics - PDF format, 4.5 meg.
• System7 CPU/Driver Board layout - PDF format, 80k.
• System6/7 sound board Schematics - PDF, 300k.
• System6/7 speech board Schematics - PDF, 150k.

• System6 Troubleshooting (Tri-Zone to Gorgar, Dec 1979)
• System6 Troubleshooting (Firepower and later, Mar 1980)
• System6 Troubleshooting (Firepower and later, Mar 1980)
• System7/8 Troubleshooting (Jun 1984)

Fixing electronic pinball games will require a few tools. Luckily, most are not that specialized and are easy to get.

Non-Specialized Tools Required:

• Work Light: clamp style lamp
• Screwdrivers: small and medium size, phillips and flat head
• Nut Drivers: 1/4", 5/16", and 11/32"
• Wrenches: 3/8", 9/16", 5/8" required, other sizes suggested
• Allen Wrenches: get an assortment of American sizes
• Needle Nose Pliers
• Hemostat. Handy for holding parts and springs. Best to have both the curved and straight versions if possible.

Specialized Tools Required:
These specialized electronics tools are needed. Please see http://marvin3m.com/begin for details on the basic electronics tools needed.

• Alligator clips and wire. Buy these at Radio Shack, part number 278-001, $3.69.
• Soldering Iron.
• Rosin Core 60/40 Solder.
• De-soldering tool.
• Digital Multi-Meter (DMM).
• Logic probe.
• Hand Crimping Tool: Molex WHT-1921 (part# 11-01-0015), Molex part# 63811-1000, Amp 725, or Radio Shack #64-410.

Cleaning "Tools" Required:

• Novus #2 or MillWax (for cleaning playfields and rubber)
• Novus #3 (for polishing metal parts)
• A hard paste wax (Trewax) or hard automotive Carnauba wax (for waxing playfields and cleaning rubber)
Novus is available at many places (my local grocery store sells it), or from any good pinball vendor. I don't recommend MillWax, but others like it (mostly because they have been around for a LONG time and are used to it). Do not use any Wildcat products or CP-100! They react with plastic and can yellow ramps and lift mylar. Trewax or Meguires Carnauba Wax is available at Walmart or the local hardware store.

When fixing electronic pinballs, I would highly recommend having some parts on-hand to make things easier and cheaper. All these parts are available from a pinball retailer.

Parts to have:
• Fuses: I would have five of any needed value on hand at all times.
  Get 250 volt fuses, not 32 volt (32 volt fuses are for cars). Radio Shack sells fuses for a decent price. Slow-blo fuses are known as MDL fuses. Fast-blo fuses are known as AGC fuses. Though fuses are game specific to some degree, here's a list that covers most system3 to system7 games:
  • 1/4 amp slow-blow
  • 2.5 amp slow-blow
  • 4 amp slow-blow
  • 5 amp slow-blow
  • 7 amp slow-blow
  • 8 amp slow-blow
  • 10 amp slow-blow
  • 10 amp fast-blow
  • 15 amp fast-blow
  • 20 amp fast-blow
Transistors:
• TIP102 transistors (replaces TIP120, coil driver).
• 2N4401 transistors (coil pre-driver).
• TIP42 transistors (lamp matrix columns).
• 2N6122 (or TIP41 or NTE196) transistors (lamp matrix rows).
• 2N6427 (or MPSA14) transistors (lamp matrix rows and column pre-drivers).
• MJE15030, MJE15031 transistors for the high voltage power supply.
• MPSD52 (or NTE288, 2N5400, 2N5401) transistors for the high voltage power supply.
• MPSD02 (or NTE287, MPS-A06, MPS-A42) transistors for the high voltage power supply.
• 2N5060 Silicon Controlled Rectifiers (lamp matrix).
Diodes and Bridges:
• 1N4004 diodes (used on coils).
• 1N4148/1N914 diodes (used everywhere!)
• 1N4763 diodes (91 volt) for the high voltage power supply.
• 1N4730 (3.9 volt 1 watt) diodes for the high voltage power supply.
• 6A4 diodes (6 amp, 400 volts) for the system3-system6 power supply.
• Bridge Rectifiers 35 amp, 200 volt (or higher) with lug leads.
Capacitors:
• 12,000 mfd (Sys3-6) or 18,000 (Sys7) mfd 16 volt axial capacitors. Used for the +5 volt filter cap.
• 100 mfd 150 volt axial capacitors for the high voltage section of the power supply.
Resistors:
• 1.2K ohm 1/2 watt resistors for the power supply.
• 39k ohm 1 watt flame-proof resistors for the power supply.
• 27 ohm 5 watt sand or ceramic wire wound resistors. Eight used per driver board for the feature lamps.
Chips:
• 6800 CPU chip: for System3 and System4 CPU boards only. Can also use the 68B00, which is a faster 2mHz version of the 6800.
• 6802/6808 CPU chip: for System6 and System7 CPU boards only. The 6802 can be replaced with the 6808. The 6802 is better than the 6808 because the 6802 has onboard RAM, but purchase whatever is cheaper or easier to get.
• 6821 or 6820 PIA chip: Used at IC18 on the CPU board for the score displays (and IC36 for sound on the System7 CPU board), and on the driver board at IC5 (coils), IC10 (lamp matrix), and IC11 (switch matrix). Have several around as this is a commonly failed chip. The 6820 is obsolete, replaced by the 6821, but either will work. Also the 68A21 or 68B21 will work.
• 7402 or 74LS02 chip: a common TTL (transistor to transistor logic) chip for the solenoid drives.
• 7406 or 74LS06 chip: a common TTL (transistor to transistor logic) chip for the lamp matrix rows and switch matrix drive (outputs).
• 7408 or 74LS08 chip: a common TTL (transistor to transistor logic) chip for the lamp matrix columns and solenoid drives.
• 8T28 (MC6889) or NTE6889 chip: obsolete, but not too hard to find, and two can be elminated with some CPU board modifications.
• 8T97 (MC6887) or 74LS367 chip: a common replacement for the 8T97 (MC6887) chip is the 74LS367.
• 8T98 (MC6888) or 74LS368 chip: a common replacement for the 8T98 (MC6888) chip is the 74LS368.
• MC6875 chip: a dedicated 6800 clock generator on System3/System4 CPU boards, obsolete. Luckily this chip doesn't die often.
• 4049 chip: a common CMOS chip for the switch matrix returns (inputs).
• 4069 chip: a common CMOS chip for the master score display board.
• 5101 CMOS RAM chip. Used on the CPU board at IC19, this RAM chip holds settings and bookkeeping totals. Any speed 500ns or less will work. A commonly failed part.
• 6810 RAM chip. Used on the CPU board at IC13, IC16 for System3 to System6.
• 2114 RAM chip. Used on the CPU board at IC13, IC16 for System7.
• UDN6118A-1/UDN6184A score display driver chip. The UDN6118A-1 replaces the obsolete UDN6184A. The UDN6118A (without the "-1") is a slightly lower voltage version (85 volts), but usually works.
• UND7180A score display driver chip. The "A" denotes a plastic case (instead of ceramic). Expensive!
• Machine pin SIP sockets, used for replacing chips (cut to size needed).
Connectors:
• .156" board mounted, "KK" bottom entry female, Phosphor bronze tin plated, female connector Molex #09-62-6104 or 09-52-3102 (10 pin), for interconnector.
• .156" connector male header pins Molex #26-48-1241 or 26-48-1101 (10 pin no lock), for interconnector. Note extra long varieties of this connector are available from Great Plains Electronics, Molex part number 10-01-2270.
• .156" Trifurcon connector terminal pins Molex #08-52-0113.
• .156" connector header pins Molex #26-48-1155 (15 pin, with lock, cut to size).
• .156" connector housings Molex #09-50-3151 (15 pins, cut to size).
• .156" connector housing polarizing pins Molex #15-04-0220.
• .156" connector terminal pin removal tool. If you are replacing IDC connectos often you can re-use the IDC plastic housing using the Molex 11-03-0016 removal tool to get out the old pins. If you are re-using the IDC plastic housing with crimp-on terminal pins, you can not use Trifurcon crimp pins. Instead you will need Molex 08-52-0072 crimp terminal pins. I don't really recommend this approach as the Trifurcon pins are much better than the single sided 08-52-0072 pins.
Other:
• #47 light bulbs: have 20 or so around. Fifty is plenty to do most games. I suggest using #47 bulbs instead of #44 bulbs, as they consume less power and produce less heat, and put less stress on the connectors and driver board.
• #89 flash bulbs: have 10 or so around.
• 3.58 or 3.579545 mHz crystal (sometimes a lead breaks, or it's just missing!)
• Nylon Coil Sleeves: the longer 2 3/16" length (part number 03-7066-5) are used when rebuilding flippers. The 1.75" length (part number 03-7066) are used for pop bumpers, etc. Sleeves with a lip (part number 03-7067-5) and tubing on each side (known as an "inline" sleeve) are used on the knocker, ball popper, etc. Also 03-7067-7 sleeves are used on drop target reset coils.
• Ball shooter sleeve, part number 03-7357.
• Flipper parts (this will be updated later).
• Shooter Spring: the short chrome spring on the outside of the shooter mechanism (part number 10-149). These rust and look like crap in short order.
• 1 1/16" Pinballs: a new pinball will make your playfield last longer.
• Leg Levelers: replace those old crummy looking leg levelers with brand new ones. 3" are used on solid state games.
• Rubber Rings: you can order game-specific ring kits with exactly the rings you need. Don't forget to get flipper rubbers and a shooter tip.

All parts, schematics and manuals are available from many sources. Please check the parts and repair sources web page for details.

Here are the list of games and their system generations. This is important to know before beginning repair. Games listed in chronological order. The manuals and other game informational links below all came from www.gamearchive.com/Pinball/Manufacturers/Williams/, so if a link is dead below check at gamearchive.com for the correct link.

Williams System 1 (not covered in this manual)

• Grand Prix, 11/76
  First Williams prototype electronic game made from a converted EM Grand Prix, only one or two produced.

Williams System 2 (not covered in this manual)

• Aztec, 11/76
  Second Williams prototype electronic game made from converted EM Aztec games, less than ten produced.

Williams System 3
Six digit score displays.

• Hot Tip, 11/77, #477, 6203 produced.
  Also made in an Electro-Mechanical version.
• Lucky Seven, 3/78, #480, 4252 produced.
  Also made in an Electro-Mechanical version.
• World Cup, 5/78, #481, 6253 produced.
  first Wms game with electronic sound (though some shipped with chimes).
• Contact*, 5/78, #482, 2502 produced.
• Disco Fever, 8/78, #483, 6000 produced.

Williams System 4


• Phoenix, 11/78, #485, 6198 produced.
• Pokerino*, 12/78, #488, 1501 produced.
• Flash, 1/79, #486, 19505 produced.
  some last made games shipped with System6 boards due to Flash's very long production run. First game with continuous background sound.
• Stellar Wars*, 3/79, #490, 5503 produced.
  some last made games shipped with System6 boards.

Williams System 5


• The "lost" system, no known games produced (perhaps a shuffle alley?)

Williams System 6


• Tri-Zone, 7/79, #487, 7250 produced.
• Time Warp, 9/79, #489, 8875 produced.
• Laser Ball*, 12/79, #493, 4500 produced.
• Gorgar@, 12/79, #496, 14000 produced.
  first talking pinball game.
• Firepower@, 3/80, #497, 17410 produced.
• Blackout@, 6/80, #495, 7050 produced.
• Scorpion*, 7/80, #494, 2000 produced.
• Alien Poker@, 10/80, #501, 6000 produced. This is a System6 with seven digit displays!
• Algar*, 11/80, #499, 349 produced.
  This is a System6 with seven digit displays!

Williams System 7 (seven digit score displays)


• Black Knight@, 12/80, #500, 13075 produced.
• Jungle Lord@, 2/81, #503, 6000 produced.
• Pharoah@, 5/81, #504, 2500 produced.
• Solar Fire, 7/81, #507, 782 produced.
• Barracora, 9/81, #510, 2350 produced.
• Hyperball, 12/81, #509, about 4900 produced.
• Cosmic Gunfight, 6/82, #502, 1008 produced.
• Varkon, 7/82, #512, 90 produced.
• Warlok, 10/82, #516, 412 produced.
• Defender, 12/82, #517, 369 produced.
• Time Fantasy, 1/83, #515, 608 produced.
• Joust, 4/83, #519, 402 produced.
• Firepower II, 7/83, #521, 3400 produced.
• Laser Cue, 2/84, #520, 2800 produced.
• Star Light, 8/84 #530, 100 produced.
  some made with system 9 boards.

Williams System 8 (not covered in this manual)

• Pennant Fever (pitch & bat), 5/84, #535

Williams System 9 (not covered in this manual)

• Space Shuttle@, 12/84, #535
• Sorcerer@, 5/85, #532
• Comet@, 6/85, #540

Williams System 10 (not covered in this manual)


• Direct Hit, a "mechanical video game". Player tried to keep a ball suspended in a tube by manipulating air pressure on it. Game never produced beyond prototype stage.

* "Wide body" games.
@ Games with speech.

Much of the following information is thanks to Mark, and is from his web page at pinball.flippers.info/system6resources.asp


Williams introduced its first Solid State pinball machine in late 1977, called Hot Tip (was also released in an electro-mechanical version). All Williams Solid State games from the 1977 Hot Tip to the 1984 Star Light shared the same basic board design.

1977 to 1984 Williams Solid State games are referred to by the revision number of their CPU board. The part number in the artwork of the CPU board (usually in a corner of the board on the front) has the "system" number after the dash: -3, -4, -6, -6A. Note System7 CPU boards did not use this convention, but these are easy to tell from system3 to system6 CPUs (because of the extra 6821 PIA chip and 7-segment LED). Along with CPU revisions, other revisions were made to the sound boards, displays, display driver boards, and power supplies. At times it can be confusing to know which board goes with which system, and what parts are interchangeable among systems. The following is a brief time-line in the evolution of the Williams Solid State games.

The CPU board number in the lower left corner, showing a System6a revision (Firepower). This was done on System 3 to System6a CPU board. System7 CPU boards do not use this numbering scheme, but are easily identified by the 7 segment LED display.

The System7 CPU board number 5764-09465-X4 in the upper left corner.

System 1 and System 2 (not covered in this manual)
In 1976 Williams tried their first attempt at a solidstate pinball. Using a converted EM Grand Prix, they made one or two prototype games using their "system 1" boardset. Just after that, Williams went to their system 2 boards, using converted EM Aztec games. About ten prototype Aztec games were produced.

System 3
Introduced commercially in 1977 with Hot Tip, the System3 system was Williams first production Solid State pinball design, and used the 6800 CPU processor chip. Hot Tip and the second Solid State game, Lucky Seven, did not have electronic sound, but used coil activated (a la electro-mechanical) chimes for sound. In a very strange move, with Williams' first two electronic games, they put a single score reel (with no numbers!) in the bottom cabinet of Hot Tip and Lucky Seven, called the "noise maker" in the schematics. The score reel advanced when points were scored to make a familar pinball noise, so the player would hear the same type of sounds they were used to with EM (electro mechanical) pinballs. Electronic Sound was introduced in 1978 with the third system3 game World Cup, and the bottom cabinet score reel was dropped. The sound board on all system3 and system4 games up to Tri-zone was located in the lower cabinet and not the backbox, so the sound board mounted volume control could be easily accessed. All system settings are set using CPU board DIP switches. Used two 512 byte PROMs for the game ROMs at IC21 and IC22, and two 2716 EPROMs or 2316 masked ROMs as the "flipper ROMs" at IC17,IC20. Note there is no socket at position U14, though the board does have the solder pads for U14. Also there are no provision for a sixth ROM at IC26 (just below the battery holder); not even solder pads. Battery holder, as the CPU board is positioned in the game, is on the middle left. System3 CPU boards can be modified to run System3 or System4 or even often System6 (but not Firepower) firmware. System3 CPU boards were installed in Hot Tip, Lucky Seven, World Cup, Contact and Disco Fever.

System 4
The System 4 CPU board was introduced in 1978 with Phoenix and incorporated several major internal enhancements, such as an improved reset circuit. The 6800 CPU processor was retained, along with it's external clock chip (the now obsolete and impossible to find) MC6875. With Flash in 1979, Williams introduced the concept of continuous background sound (and a corresponding new sound card). Game options now set via the front door switches instead of CPU board DIP switches (though the DIP switches still exist so System 4 CPU boards are downward compatible to System3). An additional ROM socket was added at IC14, which allowed the use of a 2716 EPROM there (2048 bytes), instead of using two 512 byte PROMs at IC21,IC22. Hence System 4 CPU boards used either two 512 byte ROMs at IC21 and IC22, or one 2716 EPROM at IC14, and always use two 2716 EPROMs or two 2316 masked ROMs for the "flipper ROMs" at IC17,IC20. There is also an additional sixth ROM socket added on the board at IC26, just below the battery holder. Battery holder, as the CPU board is positioned in the game, is on the middle left. System4 CPU boards can run either System3 or System4 firmware and most System6 firmware, but can not run System7 firmware. System4 CPU boards were installed in Phoenix, Pokerino, Stellar Wars and Flash.

There is also a "System 4-" (as it is often called) CPU board too. This is the same as a "regular" System 4 CPU board, but there are no sockets at IC14 and IC26. The solder pads are there, but no sockets were installed.

System 5
The "lost" system. Can not document any games that used this system. But it is speculated there were some prototype non-pinball (shuffle alley) games designed with these boards.

System 6
The System6 board was introduced in late 1979. Quite a few major internal enhancements were made on this board, and it was the most widely produced Williams CPU board ever (almost 100,000 units made). The System6 CPU board has a different layout than the earlier System3/4 boards, and included a memory protection circuit. Williams upgraded to the 6802/6808 CPU processor, which allowed them to simplify the clock circuit (the MC6875 clock chip was no longer needed, as this is built right into the 6802/6808 chip). Also Williams introduced speech into the Pinball World in 1979 with Gorgar and its seven word vocabulary. System6 games used three 512 byte ROMs at IC21,IC22,IC26 or one 2716 EPROM or 2316 masked ROM at IC14. The flipper ROMs lived at IC17,IC20 as two 2716 EPROMs or two 2316 masked ROMs. The only exception to this layout was Firepower, which used 512 byte PROMs at IC21,IC22,IC26 AND a 2716 EPROM at IC14 (CPU board jumper J4 must be installed, and J3 be removed for this configuration). There is also a modification to the CPU board for Firepower to use a single 2732 EPROM at U14 (and no ROMs at IC21,IC22,IC26), plus the two 2716 flipper EPROMs at IC17,IC20 (see the ROM section of this document for info on that). Battery holder, as the CPU board is positioned in the game, is now on the bottom right by the test switches. System6 CPU boards can run System3, System4 or System6 firmware, but can not run later System7 firmware. System6 CPU boards were installed in Flash (end of the production run), Tri-Zone, Time Warp, Gorgar and Laserball.

System 6a
A minor revision was made in the System6 CPU board where the buffer chips IC9 and IC10 were removed. System6a CPU boards were installed in Firepower, Blackout, Scorpion, Algar and Alien Poker.

System 7
The System7 board was introduced in late 1980 with Black Knight (early production Black Knight games use a System6 power supply). Again, used the 6802/6808 CPU processor. To the casual observer, a System7 game could be identified by its use of seven digit numeric displays (system3 to system6 used six digit numeric displays, except for Alien Poker & Algar). With the exception of the sound board, all of the major components were revised from previous games. Williams attempted to maintain backwards compatibility with the System7 board, however it required some soldering (jumper changes) on the board and ROM revisions to allow it to work in earlier games. Later System7 games switched from a 28 volt Flipper coil to a 50 volt Flipper coil, adding an additional power supply and transformer to the game. Most System7 CPU board are jumpered to use three 2716 EPROMs at IC14,IC20,IC26 and a single 2532 EPROM at IC17, except for Defender and Hyperball. System7 CPU boards are downward compatible, and can run any System3 to System7 software (if the CPU board is jumpered correctly, and the EPROM chips formatted correctly).

Important note about Hyperball: the CPU, power supply, and display board are all standard System7 boards (though the CPU does need the ROM jumpers changed if going into another game). But the Hyperball driver board is unique to this game, and can not be converted to work in any other Williams pinball.

System 8 (not covered in this manual)
This system was only used on one game in 1984, a pitch and bat called Pennant Fever.

System 9 (not covered in this manual)
The System 9 board was introduced in 1984 with Space Shuttle and marked the first major architecture change for Williams since its introduction of Solid State games. The concept of using separate CPU, Driver and Sound boards was replaced with a single board. Externally, a casual player wouldn't notice any difference between a System7 and System9 game as they both used 7 digit numeric displays. The only components backward compatible on a System 9 game were the power supply (to System7), the 7 digit score displays, and the seven digit master display board (to system7 only, except for some late Comet games that used differnt connectors).

System 10 (not covered in this manual)
Used on only one game call Direct Hit, a "mechanical video game". Player tried to keep a ball suspended in a tube by manipulating air pressure on it. Game never produced beyond prototype stage, so really there is no population of games with this system of boards.

Flipper ROMs.
Flipper ROMs were used in all Williams electronic games of this era. They are basically the "BIOS" of the computer system; 'generic' code that was used across a series of games, which basically made the pinball machine system "run". Additional ROM(s) were game roms, which were more or less the "rules" or "personality" of the particular game that the board was installed in. Bally and Stern are the same way, except they use U6 (and sometimes U5) as the "flipper ROM", or "BIOS" of the system. U1 and U2 were the "personality" chips.

Originally it was thought the term "flipper ROMs" were named so to distinguish them from the "shuffle ROMs", since shuffle alleys used the same CPU/driver board, but alledgedly different operating system ROMs. But according to Larry Demar, this story is untrue, as the shuffle alleys did in fact use the same "flipper ROM" operating system as the pinball games. So the origins of the name "flipper ROMs" is unknown.

The flipper ROMs were identified by color: white, yellow, green and blue. One color for each system of games (more or less as they did overlap, but basically white=system3, yellow=system4, green=system6, and blue=system7). The big exception to this rule was World Cup. This game used a unique flipper ROM 2 at IC17, different than the other four color groups of flipper ROMs. Without this special flipper ROM, World Cup will not boot. There were always two flipper EPROMs on the CPU board at IC17 and IC20 (both 2716 EPROMs or 2316 masked ROMs, except on System7 which had one 2532 EPROM at IC17). Note in many System7 games IC20 was mislabeled (make sure the 2532 EPROM goes in IC17, and the 2716 EPROM in IC20).

What Works with What System?
Here is a brief rule of thumb for part compatibility between Williams Solid State games.

• System3 through system6 games share the most compatibility. They all use the same driver board, displays and display driver, and the CPU and driver boards are downward compatible.
• CPU boards are backwards compatible, in that you can use a System6 board from a Time Warp in a Hot Tip (providing the correct game ROMs and Flipper EPROMs are installed). Even a system7 CPU (with the additional PIA chip) can be used in older System3 games. System3 and System4 CPU boards can be upward compatible and used in System6 games, with some modifications to allow for larger game ROMs, but they will not work in system7 games.
• Driver board are also downward compatible (expeption: Hyperball, which used a unique driver board). But older driver boards can be used in newer system3 to system7 games with a small modification. System3 driver boards had 1000 ohm switch matrix resistors R204-R211, a slightly later driver board version had 330 ohm switch matrix resistor, and the last (System7) version had zero ohm switch matrix resistors. The decrease in switch matrix resistor ohms was done to increase the current drive through the switch matrix (so a switch or connector with high resistance that was quickly closed would still be sensed by the CPU board). A System7 driver board can be used in System3 through System6 games (it is downward compatible). However, do not use a System3 to System6 Driver Board in a System7 game (unless modified), as the switch matrix may not be read properly. Because of this, it is best to use zero ohm switch matrix resistors in any System3 to System7 driver board, so it can be used in any game.
• Early power supplies (first two System3 games, Hot Tip and Lucky Seven) also contained a 300 volt feed for the display driver, and a power supply mounted fuse for the GI circuit. Both of these were dropped starting with World Cup (the third System3 game). But power supplies are largely interchangeable between system3 and 6 games. System7 power supplies, though plug compatible with system3 to system6, had three added connectors 3J7,3J8,3J9 for the added GI relay and GI power. These three system7 power supply plugs would not be used if installed in a system3 to system6 game.
• Transformers on earlier games also used slightly different plug arrangements. Again, the first two system3 games (Hot Tip, Lucky Seven) had a 300 volt display feed and the GI circuit going to the power supply board. World Cup to Algar (last system6 game) tranformers are interchangable, as these games had direct connections to the fuse block for the GI circuit, and no 300 volt feed. System7 games again routed the GI power through the power supply board. If swapping transformers, make sure the GI power is routed properly. Also note that system3 to system6 games had the transformer mounted in the backbox. For System7, Williams moved the transformer to the lower cabinet, probably to lower backbox heat. Finally, the last three System7 games (Firepower2 and later) had a transformer that also output 48 volts AC for the flippers (so earlier transformers can not be used in these three games).
• Williams incorporated basically three different sound boards in these games (with minor revisions). World Cup (System3) through Pokerino (System4) share the same sound card, which handled basic sounds. Flash (System4) through Algar (System6) also share the same sound board (these board supported continual background sound). And Gorgar (System6, first game with speech), Firepower, Blackout, Alien Poker, Black Knight (System7, except for early production BK's), Jungle Lord, and Pharoah used a sound board with an added speech board. System7 games Solar Fire and later went back to the System6 era sound card, and did not have speech. This System7 sound board was the same sound board as used on System6 games, with the exception of the connector for the speech board cable was missing (since these games did not have speech). Of course different games had different sound ROMs, so make sure to use the correct sound board ROMs. Note speech didn't return in Williams pinball until System 9's Space Shuttle.
• System 9 games share the same power supplies (main and flipper) and displays with System7 games. The speech boards may also look the same, but System 9 speech boards are jumpered to use 2732 EPROMs, while System6 and 7 speech boards use 2532 EPROMs.

Williams System 3 through 6 Board Design.
All Williams System 3 through 6 games share the same design architecture. For the most part, System7 games do also, with some modifications that will be discussed later.

Williams, like the other major pinball manufacturer's of the time, used what is sometimes called a "split board" design. This means the CPU and driver functions are separated onto two different boards. This was done to facilitate the field repair of the machines. The tech would only need to swap out the failing board with a replacement and take it back to the shop for repair. The prevailing thought at the time was that the driver boards were much more likely to fail then the CPU boards. If the boards had been designed as a single unit, then a tech would need to carry ROM chips for each machine on the operator's route and swap them out when replacing the board. However if the driver board were separate from the CPU board, then no ROM swap would be necessary for the majority of repairs.

This philosophy held true, as driver boards have proven much more likely to fail then the CPU. What Williams and the other manufacturers didn't bargain for however was the failure of the connectors between the driver board and CPU board. Gottlieb's had the worst problems due to its use of Personal Computer style edge connectors that relied on the thin coating of copper on the board for the interconnection. Williams boards are far from exempt however due to the decision to extend the CPUs address and data lines across the interboard connection, from the CPU board to the driver board. This requires the connector pins between the driver board and CPU board to provide high speed data transfer. But dirt and loose connectors made this a liability (remember, most connectors have a lifespan of 25 connects!) A bad interboard connection could easily crash the whole game.

All games share the same five major components, the CPU (aka MPU) board, the Driver board, the power supply, the display driver, and the score displays. All games after Lucky Seven also had a sound board, and later System6 games Gorgar and later (Blackout, Firepower, etc.) had speech boards.

All System3 and most System4 games had their sound boards located in the lower cabinet. It was a direct replacement for the chime unit (the sounds were also driven by the solenoid drivers that drove the chime coils). Williams was very paranoid about the change, thinking they might have to change back to chimes if people complained. Plus it meant the volume could be easily adjusted from the front door (no need for a remote volume control). Late System4 and later games had their sound boards located in the back box.

Inside the first two System3 games (Hot Tip). Note the connector on the lower left of the power supply board (blue circle). The yellow wires are the GI wires on this connector that nearly always burn. After Hot Tip and Lucky Seven, the GI fuse was moved to a fuse card, so there are no GI connectors to burn on games World Cup to Algar (the last System6 game). The red circle below the battery holder shows the complete lack of even solder pads for IC26 (which is present on System 4 CPU boards). The other red circles shows IC14's solder pads, but no socket is installed. Picture by Mark.

Inside a World Cup and later System3 game (Disco Fever). Note games World Cup to Stellar Wars have the sound board mounted inside the lower cabinet. Single GI fuse on the fuse card, below the power supply board. Note location of the battery holder on the CPU board. Picture by Mark.

Inside a typical System6 game (Tri-Zone to Laser Ball). Sound board now at the upper right, above the power supply board. Note the GI fuse card holders (there are now three) are still off the power supply board and above the "can" capacitor. Note the new location of the battery holder on the CPU board. Picture by Mark.

Inside a typical System7 game (Black Knight). Note newer Sound and Speech board at upper right, and the newer power supply board below it. Also the power transformer is no longer mounted in the backbox (moved to the lower cabinet to reduce heat in the backbox). GI fuses moved to the power supply board, and hence the connector on the lower right burns easily. Again, note the new location of the battery holder on the CPU board.

CPU Board
The CPU board (aka MPU board) contains the microprocessor, diagnostic and display logic. Williams games were designed around the Motorola 6800/6802 series of chips. Also contained on the CPU board are the game's ROM (Read-Only Memory) chips that contain the game specific program. The diagnostics on a Williams CPU board consists of two LEDs. A common mis-conception is that Williams boards do a complete self-test at power-on, like the 1977-1985 Bally CPU board. In reality, a "real" self-test only occurs when the test button on the CPU board is pressed!

System3/4 CPU board with the 6800 CPU chip and one 6821 PIA. Note the position of the battery holder on the left. Systems3 and System4 are essentially the same except System4 has additional ROM socket(s) (IC14 and/or IC26). This System3 CPU board has been upgraded to System4.

System6 CPU board with the 6802/6808 CPU chip and one 6821 PIA. Note the position of the battery holder on the right.

System7 CPU board with the 6802/6808 CPU chip and two 6821 PIAs. Note the position of the battery holder on the left, the single 7-segment LED display above the battery, and the added 40 pin 6821 PIA chip for sound and score display commas. The layout of the System7 board is different, but it is downward compatible to System3 to System6 games.

Driver Board and PIA Chips
The driver board is actually an extension of the CPU board. The Driver board controls the solenoids and lamps, and reads the switches. The 6802 microprocessor used in these games communicates to the rest of the game through the use of what are known as PIA chips (Peripheral Interface Adapter). These chips have the designation 6821, however early driver boards may have used 6820 chips (which can be replaced with a 6821 chip). In a personal computer, examples of peripherals are the keyboard, disk drive and modem. In a pinball game, peripherals are the displays, switches and solenoids (the switch reading mechanism in a pinball game is identical to that of the keyboard reading mechanism in a personal computer). A PIA chip has an address just like a memory or ROM chip does, and is accessed by the microprocessor in the same fashion. The game's program reads the PIA to see what switches are closed and it writes to the PIA to fire a solenoid or change the score displays.

The driver board used on system3 to system7 are nearly identical, except for the switch matrix resistors. System3 driver boards had 1000 ohm switch matrix resistors R204-R211, a slightly later driver board version had 330 ohm switch matrix resistor, and the last (System7) version had zero ohm switch matrix resistors. The decrease in switch matrix resistor ohms was done to increase the current drive through the switch matrix (so a switch or connector with some resistance that was quickly closed would still be sensed by the CPU board). A System7 driver board can be used in System3 through System6 games (it is downward compatible; the only exception to this rule is Hyperball's driver board, which is unique to that game). However, do not use an unmodified System3 to System6 Driver Board in a System7 game, as the switch matrix may not be read properly. Because of this, it is best to use zero ohm switch matrix resistors in any System3 to System7 driver board, so it can be used in any game.

The system3 to System7 driver board with three 6821 PIAs. Note the white 5 watt sand resistors on the lower right of the board, which replaced the original carbon 3 watt lamp matrix resistors (which always burn). Picture by Mark.

System3 to System6 games used four PIA chips. One PIA on the CPU board controls the score displays. On System7 CPU boards, there is an additional PIA chip which controls the sound triggers and score display commas. There are also three PIAs on the Driver board. On the driver board, one PIA controls the Solenoids, one controls the lamps, and one reads the switches. Because the PIA chips are seen as memory locations by the microprocessor, any failure of a PIA chip will most likely cause the game to lock-up because the game's program cannot read or write to these memory locations. This is also why a CPU board will not "boot" without the driver board installed (but there are special diagnostic chips available that will allow testing of the CPU board with the driver board detached).

The PIA chips are easily identifiable, as they are the large 40 pin chips on the board. Don't worry if the chips don't say "6821" or "6800" on them. Williams bought these chips in large quantities which were manufactured specially for them and have a proprietary designation (Bally did this too). Below are the part numbers:

• 6800 CPU: Williams part# 5A-8987, Bally part# E-620-28, Motorola part# SC44216P.
• 6821 PIA: Williams part# 5A-8972, Bally part# E-620-29, Motorola part# SC44067P.
• 6810 RAM: Williams part# 5A-9003, Bally part# E-620-30.
• 6808 CPU: Williams part# 5A-9150.

The electrical current used in a pinball game would fry a 6821 PIA in short order. To prevent this, a series of IC (integrated circuit) chips and transistors are used as buffers between the PIAs and the rest of the game. These chips also provide other controls.

Power Supply
There are actually multiple independent power circuits in the game. Some power circuits do "daisy chain" though.

All games System3 through System7 have the following power circuits:

• +5 volt DC regulated logic power
• +12 volt DC unregulated (Williams calls this the "unregulated 5 volts")
• +100 and -100 volt DC display power
• +28 volt DC (or +50 volt DC, depending on the game) solenoid and flipper power
• +18 volt DC lamp matrix power
• 6 volt AC General Illumination (GI) power
• 300 volts DC (used on just the first two System3 games)
• -12 volts DC, System7 and newer power supplies.
• 50 volts DC, System7 games Firepower2 and later only (for the flippers).

System6 power supply (Firepower), no GI fuses, no GI relay, no GI connectors!

System7 power supply (Black Knight), has GI fuses, GI relay, and GI connectors (which are usually burnt, like on this game, in the lower right).

System7 Lamp matrix and solenoid bridges, and the lamp matrix filter capacitor (Black Knight). Note there is no GI relay next to the large capacitor on this Black Knight (the GI relay is mounted on the System7 power supply board).

The G.I. relay on BlackOut, Scorpion & early Black Knights with System6 power supplies is mounted in the bottom of the backbox (System6 power supply boards do not have a power supply mounted GI relay). Picture by Mark.

The two bridge rectifiers bolted to the backbox are for Solenoid and Lamp matrix power, and have nothing to do with the logic (CPU) power. Same goes for the large capacitor mounted in the back box, its used for the lamp matrix power only.

Another often confused area is the value of the +12 volt unregulated power circuit. First, Williams calls this the "unregulated 5 volts" (but really it's unregulated 12 volts that gets knocked down to about 5 volts by the CPU board). Since it is not regulated, it will vary depending on the line voltage. It can range anywhere from 10 to 14 volts, and this is normal (some novice repair people will attempt to repair their power supplies because the 12 volts supply is only 11 volts).

Flipper power supply board, as used in the backbox on Firepower II, LaserCue and Starlight. This powered the flippers at 50 volts instead of 28 volts like all the other coils. This made these late System7 and later Williams games have very snappy flippers. Picture by Frank.

Also the last three System7 games (Firepower2, LaserCue, Starlight) had a separate flipper power supply board installed in the backbox. This board took 48 volts AC from the transformer and converted it to 50 volts DC just for the flipper coils.

Sound Board.
The first two Williams Solid State games, Hot Tip and Lucky Seven, continued to use chimes, like the electro-mechanical games. World Cup was the first Williams game to use electronic sound. Sound boards are actually self-contained computers, complete with their own power supply, micro-processor and PIA. The game really doesn't even see the sound board. Instead it activates sounds on the sound board through driver board solenoid transistors, using the same controls on the driver board to trigger different sounds as it would to fire a solenoid. System3 and System4 games had the sound board mounted in the lower cabinet, and not in the backbox.

The first generation system3/4 sound board.

Games from World Cup (System3) to Pokerino (System 4) used a sound board that would generate a sound when an activity (scoring) occurred (note early World Cup games still had chimes). However when the ball wasn't hitting anything, no sound was produced. Starting with Flash (System 4), a revised sound board was used that would generate constant or continuous background sounds. These usually varied in pitch as scoring increased, giving the player an adrenaline boost when things really got going.

Gorgar (System6) introduced speech to the pinball world. A redesigned sound board featured a connector for the optional add-on speech board module. This sound board was used on all games from Gorgar to the end of System7. But games with speech (Gorgar, Firepower, Blackout, Alien Poker, Jungle Lord and Pharoah) used an additional speech board. System7 games without speech (Solar Fire and later) used the System6 sound board (but the connector to the not-used speech board was missing). These were dark days for Williams pinball, and the added expense of a speech board prohibited their use on many System7 pinballs.

Note the System7 CPU board now had an additional PIA chip just for triggering sound (and for commas in the score displays). This freed up the driver board sound transistors for driving playfield solenoids, making System7 games more complex than earlier games.

System6/7 sound and speech boards (Black Knight).

Displays
Williams used a standard six digit gas filled display in all system3 to System6 games. These are still widely available today. Most replacement displays today have a "nipple" where they were sealed. These will work fine as a replacement, and most display boards already have a hole drilled in them. System7 games (and the last two System6 games, Alien Poker & Algar) use a seven digit display.

Display Driver Board
The display driver board is mounted just behind the backglass on the front of the wood display panel. The display driver also contains the credit/ball-in-play display. The job of the display driver is to take the binary score data coming from the CPU board and translate into the signals understood by the displays. With System7 games, the display driver board was moved to the back side of the opening wood display panel.

There were two basic versions of the display driver manufactured (but one version actually had two different designs, so I guess there are really three different versions). All versions are compatible in all games. On version uses integrated circuits (UDN6184A-1/UDN7180A display drivers, with another version that used 22 pin NE584/NE585 display drivers). The other basic version uses "discrete" components (meaning a large number of individual transistors). The reason for the discrete component version was that the UDN6184 and UDN7180 segment driver chips used were at some point in short supply. Williams designed an alternate board that replaced the functionality of these chips with individual transistors (this happened around Flash and up to and including Firepower). The UDN6184A chip continues to be in short supply today, but can be replaced by the plentiful and cheap UDN6118A-1 display driver. The UDN7180A though is still expensive, and averages between $15 and $30 each.

Williams System 7 Board Design.
At first glance at a System7 game, it might be hard to tell any major differences between earlier games and the System7 game. The basic design architecture remained the same, however several significant improvements were made. System7 added more memory space, seven segment displays, and a direct sound drive (so it doesn't eat up solenoid drives to make sounds.) Like its brothers before it, the design was intended to be able to be used in all previous games, if necessary. So they could just manufacture and stock the latest board and anyone that needed one for an old game would be able to just order the latest board. That's why, for instance, it still had the two little LEDs on it even though it had a 7-segment display.

• The System7 CPU board has an additional PIA which is used to control Sound and Speech (and adds commas to the score displays). This freed additional solenoid driver transistors on the driver board for more solenoids, allowing for more complex games.
• System7 games (and the last two System6 games, Alien Poker & Algar) use seven digit displays and a corresponding new display driver board.
• The last three System7 games (Firepower II, Laser Cue, Starlight) used 50 volt flipper coils, instead of 28 volt flipper coils. This gave the game's flippers much power and punch.
• The power supply, a common failure point on previous games, was redesigned for System7.

Later in System7 production, the "backwards compatibility" began to disappear. Williams figured out it was costing them money to be backwards compatible on the CPU board. So the CPU's two LEDs disappeared, along with the SW2 switch and the two banks of DIP switches. This stuff can be easily added back though.

Number of Coils Available in System3 to System7 Games.
The good thing about Williams was their liberal use of coils on the driver board. Unlike Gottlieb system80, where there were basically just six solenoid driver transistors on the driver board, Williams had 16 "regular" solenoids, plus six "special solenoids" for a total of 22 usuable coils.

With the advent of system7, the number of usable coils went up. Where system3 to system6 used coils 9,10,11,12,13 as sound drivers, with system7 coils 9 to 13 were now available for other uses. This happened because the additional sound PIA chip added to the system7 CPU board now handled the "calls" to the sound board, instead of the driver board transistors doing that.

Also the added system7 CPU sound PIA gave Williams two more available solenoids, number 23 and number 24. These can be seen in the system7 coil diagnostics, but were never used in any system7 game. These existed because there were two extra unused PIA ports on the new system7 CPU sound PIA, that were set up to be used as coils in the "blue" flipper ROMs (the game's operating system). But unfortunately the system3 to system7 driver board could not use these two new coils, as there were no available driver transistors on the driver board for them. The two new coil PIA outputs also went to a never used and unpopulated ribbon cable connector on the right bottom side of the system7 CPU board. The diagnostic code was added to the blue flipper ROMs most likely because these chips were "masked" ROMs, and adding the code later (when it was actually needed) would have required making new blue flipper ROMs or EPROMs, which would have cost money. Hence we can see these two new system7 coils in the solenoid diagnostics (Williams also added coil #25 to system7 diagnostics, which was the flipper relay). If Williams ever needed these two new coils on a system7 game, they could have populated the ribbon cable connector on the system7 CPU board, and had a mini auxiliary driver board with driver transistors (as was done on some 1990s games like Twilight Zone, Star Trek Next Generation, Demo Man, etc.) Also the use of this new system7 CPU board ribbon cable connector could have eliminated the .156" Molex interconnector, which gave these game reliability problems. But that would have required a new driver board to accept this ribbon cable, and that never happened.

After setting up a System3 to System7 game, before powering on, double check the cabinet/playfield to backbox connectors! (Connectors at the head/body split.) Williams makes it so connectors can not be put together incorrectly, as they're all different shapes and sizes, right? Well, not quite! The COLORS of the connectors need to be noted too. Specifically, there is a pair of white connectors and a pair of black connectors that are physically identical. IMPORTANT: Make sure to get the right colors together! If these connectors are cross-connected, the solenoid voltage (28 volts) will be applied to the +5 volt logic. This will instantly fry numerous chips on the CPU and driver boards, and even the sound board. The short story here is to make sure the head/body female white plug goes to a male white plug. Same thing for the black plug set too.

The plug compatible black and white connectors (Firepower). Plug these together incorrectly, and the CPU/driver/sounds boards will be wasted in a flash!

BUT WAIT! It's also a good idea to check the wire colors too. At the plug connectors, the mating wires on the female and male plugs should be the same wire color. Though certainly not common, Williams has mistakenly mixed the plug colors. Remember, the wire colors matching is more important than the plug colors matching! But it can be assumed that 99% of the time Williams used the correct plug colors, so matching plug colors is a good approach. On the other hand, see the picture below where Williams used two *white* connectors of the exact same type. The only way to match these connectors is by wire color! So the safe and sane person will always verify the wire colors match on both the male and female connectors, before turning the game on!

Oops! Williams assembled this Black Knight with two identical *white* connectors (instead of one white and one black). The only way to match these plugs is by wire color. Again, plug these together incorrectly, and the CPU/driver/sounds boards will be wasted in a flash!

Oops! I Mis-Connected the Plugs and Turned the Game On!
If the plugs were cross-connected, and the game turned on, there are some likely things that could happen (this example is Black Knight; what blows exactly can be game specific, and may also depend on how long the game was powered on). First the obviously broken stuff was:
• General Illumination lights.
• Score displays unlit.
• Flippers permanently energized and stuck on.
• Drop target reset coil energized and stuck on.
• Sound board wouldn't even do self test.
• Blows fuses.

In this Black Knight example, here's what fried, and what survived:

• Power supply board was OK.
• Sound board Amp IC blown (flipper was being energized through this IC).
• CPU board needed IC7 (7404) and IC5 (7402) replaced, as these were shorting +5V and ground through them (these are connected to the memory protect circuit and diagnostic switches). It also needed IC12 (7408) replaced to get the CMOS RAM working again (until this was replaced, the game always came up in test mode).
• Driver board needed IC17 (7406) replaced to fix a bunch of switches that wouldn't read. Also needed IC11 (6821 PIA) replaced to fix some row inputs that were stuck "on" (surprisingly, the 4049's CMOS chips survived)

So the moral of the story is, "don't cross-connect the connectors"!

Loose/Broken Wires in the Connectors.
When assembling the game, carefully check all of the connectors between the head and the cab. Sometimes a connector pin will slip out of the plastic connector housing, or a wire will break very close to where it is crimped to the connector pin. This can cause a great deal of frustration when a "it was working before" game now does not work, after it is moved.

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 addition white-with-red trace grounding wire coming from the playfield that needs to be cinched under the wing nut in addition to the braided ground wire.

A very good idea for any unknown game just purchased is to check all the coils' resistance. If the game is new to you, and you have not powered it on, a quick check of coil resistance will tell you a lot about your new game. This takes about one minute and can save you hours of repair and diagnosing work.

Any coil that has locked on (usually due to a short solenoid driver board transistor) will heat up and have a lower total resistance. This happens because the painted enamel insulation on the coil's wire burns, causing the windings to short against each other. This will lower the coil's resistance, causing the coil to get even hotter. Within a minute or so the coil becomes a dead short, and usually blows a fuse.

If the solenoid driver board (SDB) transistor is repaired, and the game is powered on with a dead-shorted coil, this will blow the SDB's same transistor again when the coil is fired by the game for the first time! There is no sense making more work for yourself. So take 60 seconds and check all the coils' resistance BEFORE powering the game on for the first time.

In order to check coil resistance, put your DMM on its lowest resistance setting. Then put the DMM's red and black leads on each coil's lugs. A resistance of 2.5 ohms or greater should be seen. Anything less than 2.5 ohms, and the coil and/or driving transistor may be bad. Now remove the wire from one of the lugs of the coil, and test the coil again. If the resistance is still the same (low), the coil or diode is bad (and also perhaps the driving transistor). If the resistance is higher than 2.5 ohms, the coil is good but the solenoid driver board transistor is shorted and will need to be replaced. Lastly, the coil's 1N4004 diode could be shorted too, giving a false low coil resistance. Cut one diode leg from a coil lug and retest the coil's ohms.

Remember when reconnecting the wires to the coil that the power wire (usually two wires or thicker wires) goes to the coil's lug with the BANDED side of the diode attached. The thinner wire is the coil's return path to ground via the driver transistor and attaches to the coil lug with the non-banded side of the diode attached.

If a low resistance coil is found, also suspect the associated driver board transistor as bad. A low resistance coil is a red flag, a warning, that there may be problems on the driver board.

IMPORTANT! Before Turning the Game On!
After all the above items in section two ("Before Turning the Game On") have been inspected and fixed, now it is finally time to actually power the game on! But before proceeding, remove the Lamp matrix and Solenoid fuses from the game (fuses F2 and F3 on the power supply board). This is VERY important! If there are problems on the CPU or driver board, having these fuses removed will prevent any further damage to the game.

For example, when the CPU board does not work, and the game is powered on, often all the coils will energize and all the lamps will lock on. This can burn the coils and lamps at minimum. The same thing can happen if the game is turned on with the CPU board missing, or if the "blanking" signal (pin 37 of the interconnector) stays low.

What if the game Locks-Up or "Resets"?
Please see the section that directly addresses this here. A complete systematic approach is shown to fix those problems. But if the modifications are performed as described in this section, this should reduce any reset or lock-up problems.

What Voltages does the Power Supply Output?
The "power supply" (that is, the transformer, the power supply board, and the backbox attached bridge rectifiers/filter capacitor) outputs the following voltages:

• +5vdc regulated logic power.
• +12vdc unregulated, often called "unregulated 5 volts" by Williams, because on the CPU board the unregulated 12 volts gets knocked down to about 5 volts.
• +18vdc lamp matrix power (for game controlled lamps).
• +28vdc solenoid/flipper power.
• +/- 100vdc score display power.
• 6.3vac General Illumination lamp power.
• +50 volts DC (for flippers), Firepower2 and later, via an additional flipper power supply board.

The power supply board takes in 18.6 volts AC (9.3 volts AC times two) from the transformer, and outputs +12 volts DC, and +5 volts DC. In addition it takes in 90 volts AC from the transformer and outputs +/- 100 volts DC. The unregulated 28 volts DC for the solenoids and the 18 volts DC for the lamp matrix power actually does not use the power supply board (this is handled by the backbox mounted bridge rectifiers and filter capacitor). But these two voltages do go through the power supply board for fusing, but neither is manipulated or altered. On System7 power supplies, 6.3 volts AC also comes into the power supply board, but only to provide a fuse and a G.I relay to the circuit (there are three additional connectors on a system7 power supply for GI input and output, and for control of the GI relay). Also note that the Sound Board has its own dedicated power supply. So if the sound is not working, don't mess with the game's main power supply.

Early power supplies (first two system3 games, Hot Tip and Lucky Seven) also routed the G.I. through the power supply board, and contained a 300 volt feed for the display driver that was later dropped. All power supplies boards from System3 to System7 are interchangeable (except for maybe the first two system3 game power supplies which used the 300 volt feed and GI power supply connector).

Transformers on earlier games also used slightly different plug arrangements. Hot Tip/Lucky Seven and System7 games routed the GI power through the power supply board. System3 (World Cup and later) to System6 games had direct connections to the fuse card for the GI circuit. If swapping transformers, make sure the GI power is routed properly through the fuse card or power supply, as dictated by the game in question. Also the last three System7 games (Firepower2, LaserCue, Starlight) used 50 volt flipper coils (compared to the rest of the 28 volt game coils), so these trasformers are different too.

The "power supply" on a System6 game. Picture by Mark.

Fuses.

System3 and 4 games (all games through Flash) do not have the fuse for the Flipper power on the power supply. Instead the fuse is located under the playfield near the flippers. Fuse holder F4 is present on the power supply on these games, but the circuit isn't used on games from World Cup through Flash, so fuse F4 can be removed. Likewise on the last three System7 games (Firepower2, LaserCue, Starlight); these games used 50 volt flipper coils, and had a separate 50 volt power supply board for the flippers. The F4 power supply fuse is therefore not used (instead the 50 volt flipper power supply board has a F2 fuse 5amp slow blow).

The first two System3 games from Williams (Hot Tip and Lucky Seven) use F4 as the GI fuse. These games routed the GI power through Power Supply board and the .156" connectors. The photo below shows the GI connector from a Hot Tip and the associated burn marks on the connector. Williams smartly removed the GI from the Power Supply board by World Cup, but had a lapse of judgment and put it back onto the Power Supply board in System7 games (because the power supply board also got a G.I. relay), albeit with a larger Molex connector, but the same burnt connector results.

Hot Tip/Lucky Seven showing the lower left burnt G.I. connector on the power supply board. Picture by Mark.

Main fuse: All system3 to system7 games use a main fuse of 7.5 amp fast blow in the front of the cabinet (accessed through the coin door).

System 3 Fuses.

Power Supply Fuses:
• F1 = Score display 90 volts AC, .25 amp Slow Blow.
• F2 = Solenoids 28 volts DC, 2.5 amp Slow Blow.
• F3 = Lamp matrix 18 volts DC, 8 amp Fast Blow.
• F4 = GI fuse 6.3 volts, 20 amp Fast Blow, Hot Tip and Lucky Seven only. World Cup to Flash, this fuse is not used.
• F5 = +5 volts DC logic, 4 amp Fast Blow.

Sound Board Fuses (except Hot Tip & Lucky Seven):

• F1 = 9.3 volts AC, 4 amp Slow Blow (mis-labeled 2 amp on some schematics).

Backbox Panel Fuses (located below power supply board):

• Fuse Card = 28 volt flippers, 20 amp Fast Blow (not present on Hot Tip and Lucky Seven).

Playfield Fuse (located under playfield):

• 28 volt flippers, 10 amp Fast blow, on games before Flash.

Power Supply Bridges (located on power supply board):

None.

Backbox Bridges (located below power supply board, 35 amp, 400 volts):

• 6BR1 Blue Wires = Lamp matrix 13.5 volts AC inputs.
• 6BR2 Green (or Red) Wires = Solenoids 25.5 volts AC inputs.

System 4 Fuses.
Power Supply Fuses:
• F1 = Score display 90 volts AC, .25 amp Slow Blow.
• F2 = Solenoids 28 volts DC, 2.5 amp Slow Blow.
• F3 = Lamp matrix 18 volts DC, 8 amp Fast Blow.
• F4 = Not used on games before Flash. Starting with Flash, F4 is the flipper fuse (10 amp Fast blow).
• F5 = +5 volts DC logic, 4 amp Fast Blow.

Sound Board Fuses:

• F1 = 9.3 volts AC, 4 amp Slow Blow.
• F2 = 9.3 volts AC, 4 amp Slow Blow.

Backbox Panel Fuses (located below power supply board):

• Fuse Card = 6.3 volt General Illumination, 20 amp Fast Blow.

Playfield Fuse (located under playfield):

• 28 volt flippers, 10 amp Fast Blow (games before Flash only).

Power Supply Bridges (located on power supply board):

None.

Backbox Bridges (located below power supply board, 35 amp, 00 volts):

• 6BR1 Blue Wires = Lamp matrix 13.5 volts AC inputs.
• 6BR2 Green (or Red) Wires = Solenoids 25.5 volts AC inputs.

System 6 Fuses.
Power Supply Fuses:
• F1 = Score display 90 volts AC, .25 amp Slow Blow.
• F2 = Solenoids 28 volts DC, 2.5 amp Slow Blow.
• F3 = Lamp matrix 18 volts DC, 8 amp Fast Blow.
• F4 = Flippers 28 volts DC, 10 amp Slow Blow (GI fuse on shuffle alleys).
• F5 = +5 volts DC logic, 4 amp Fast Blow.

Sound Board Fuses:

• F1 = 9.3 volts AC, 4 amp Slow Blow.
• F2 = 9.3 volts AC, 4 amp Slow Blow.

Backbox Panel Fuses (located below power supply board on a fuse card):

• 6F1 Yellow Wires = General Illumination 6.3 volts AC, 20 amp Fast Blow.
• 6F2 Gray Wires = Logic 9.3 volts AC supply, 4 amp Slow Blow.
• 6F3 Gray Wires = Logic 9.3 volts AC supply, 4 amp Slow Blow.

No playfield fuses, as the fuse F4 on the power supply board is now used for the flippers.

Power Supply Bridges (located on power supply board):

None.

Backbox Bridges (located below power supply board, 35 amp, 400 volts):

• 6BR1 Blue Wires = Lamp matrix 13.5 volts AC inputs.
• 6BR2 Red Wires = Solenoids 25.5 volts AC inputs.

System 7 Fuses.
Power Supply Fuses:
• F1 = Score display 90 volts AC, .25 amp Slow Blow.
• F2 = Solenoids 28 volts DC, 2.5 amp Slow Blow.
• F3 = Lamp matrix 18 volts DC, 8 amp Fast Blow.
• F4 = Flippers 28 volts DC, 10 amp (2 flippers) or 15 amp (3 or 4 flippers) Fast Blow (on shuffle alleys this is the GI fuse). This fuse is NOT used on Firepower2, LaserCue, Starlight.
• F5 = 9.3 volts AC (input for +5 volts), 7 amp Slow Blow.
• F6 = 9.3 volts AC (input for +5 volts), 7 amp Slow Blow.
• F7 = General Illumination for pinballs, 6.3 volts AC, 20 amp Fast Blow.

Flipper Power Supply (Firepower2, LaserCue, Starlight ONLY):

• F2 = 48 volts AC, 5 amp Slow Blow.

Sound Board Fuses:

• F1 = 9.3 volts AC, 4 amp Slow Blow.
• F2 = 9.3 volts AC, 4 amp Slow Blow.

Backbox Panel Fuses:

None, unless user added!

No playfield fuses, as the flipper fuse F4 is now on the power supply board or the flipper power supply board.

Power Supply Bridges (located on power supply board, 35 amp, 400 volts):

• BR1 = 9.3 volts AC inputs that ends up being +12 volts and +5 volts logic.

Backbox Bridges (located below power supply board, 35 amp, 400 volts):

• 6BR1 Blue Wires = Lamp matrix 13.5 volts AC inputs.
• 6BR2 Red Wires = Solenoids 25.5 volts AC inputs.

Diagnosing a Blown Solenoid Fuse.
If any of the game's solenoid fuse(s) blow immediately at power-on, here's some things to check:

• First check the pop bumpers and slingshots to see if their "activation" switches are stuck closed (the switches that the ball triggers to make the bumper work). These "special solenoids" are unlike other coils in the game in that if their activation switch is stuck closed, it will keep the coil turned on, and the fuse will blow.
• With the game off, use a DMM and check the ohm reading of each and every coil in the game. On two lug coils just put the meter leads on the coil's lugs (on three lug coils there is a "common" lug, measure the resistance between the common lug and the other two lugs). All coils should be 2.5 ohms or greater. If a coil is less than 2.5 ohms, the coil is bad and essentially a dead short, hence causing the solenoid fuse to blow.
• If the flipper solenoid fuse is blown, this is most often a bad or mis-adjusted EOS (End of Stroke) switch. See the flipper section for help with that.
• If a coil is less than 2.5 ohms, there is probably a reason this happened - the coil locked on, heated up, and melted the insulation off the coil's windings. This causes a short between the windings, and lowers the coil's overall resistance. Usually this most often due to a shorted driver transistor which keeps the coil energized while the game is powered on.
• For all coils found with less than 2.5 ohms of resistance, disconnect the wire(s) from one of the coil's lugs. For a two lug coil, there is a power wire which is usually a thicker wire or often two thicker wires. This brings power to the coil and is connected to the coil lug with the banded side of the diode attached. The other coil lug has the return wire which goes to the CPU board. I remove the thinner return wire because it is easier, but removing either will disconnect the coil from the circuit.
• Power the game on with a new solenoid fuse. Does the fuse still blow? If not, you have found the start of your problem (the bad coil - now you need to find out what made the coil bad!) If the fuse still blows, look for another bad coil or perhaps a short from the coil voltage to ground.

Adding Two Fuses to a System3 to System7 Games.
All Williams games prior to 1987 do *not* have fuses on the input side of the backbox mounted bridge rectifiers. This is a bad design, and one that Williams later fixed.

The two bridge rectifiers mounted to the backbox are the lamp matrix and solenoid bridge rectifiers. If either of these bridges shorts, or the large backbox mounted 30,000 mfd lamp matrix capacitor shorts, the main power fuse *should* blow. But if this single fuse was "over fused", a fire could result!

Added fuses in a Firepower to the input (AC) side of the solenoid and lamp matrix backbox bridges.

Williams Varkon pinball. Here the solenoid or lamp matrix bridge shorted on the input side. Without the input fuse (as the game was shipped from the factory), the red 18 gauge wires got so hot they melted! Luckily the game's main fuse finally blew, saving this game from a certain internal fire.

Here's the Varkon after the owner repaired the melted wires and added the two suggested fuses to the input (AC) side of the solenoid and lamp matrix bridges.

To fix this problem is simple. It requires two fuse holders (available at Radio Shack), two 8 amp slow blow fuses, and two pieces of 18 gauge wire. Here are the instructions:
• In the backbox, beneath the power supply board, locate the bridge with the BLUE wires (6BR1, for the lamp matrix).
• Using a 1/4" hex head sheet metal screw, mount a fuse holder right next to this bridge rectifier.
• Disconnect one of the blue wires from this bridge (either blue wire, it does not matter). Often these wires are soldered to the bridge. The blue wires are the AC input wires to the bridge.
• Solder this removed blue wire to one end of the newly installed fuse holder.
• Solder a new wire from the other end of the newly installed fuse holder, to the lug of the bridge rectifier where the blue wire was originally disconnected.

• In the backbox, beneath the power supply board, locate the bridge with the RED wires (6BR2, for the solenoids).
• Using a 1/4" hex head sheet metal screw, mount a fuse holder right next to this bridge rectifier.
• Disconnect one of the red wires from this bridge (either red wire, it does not matter). Usually these wires have lug connectors (but they could be soldered). The red wires are the AC input wires to the bridge.
• Solder this removed red wire to one end of the newly installed fuse holder.
• Solder a new wire from the other end of the newly installed fuse holder, to the lug of the bridge rectifier where the red wire was originally disconnected.
• Install 8 amp slow blow fuses in both fuse holders.

Testing a Bridge Rectifier.
The following test will check if a bridge has an open circuit or a short.

1. Turn the game off.
2. Put the DMM on diode setting.
3. Put the black lead of the DMM on the "+" (positive) terminal of the bridge.
4. Put the red lead of the DMM on either AC bridge terminal. Between .4 and .6 volts should be seen. Switch the red DMM lead to the other AC bridge terminal, and again .4 to .6 volts should be seen.
5. Put the red lead of the DMM on the "-" (negative terminal of the bridge.
6. Put the black lead of the DMM on either AC bridge terminal. Between .4 and .6 volts should be seen. Switch the black DMM lead to the other AC bridge terminal, and again .4 to .6 volts should be seen.

The Varistor and AC Line Filter.
Near the front left of the main cabinet, next to the auxiliary power plug, are the AC line and the Varistor. The Varistor is a voltage spike protection device, and looks like a large red ceramic disk capacitor. This is wired across the terminals of a small metal box (the line filter). The varistor is a one-time surge suppressor. When a power surge or voltage spike is sensed, the varistor's resistance rapidly decreases, creating an instant short path for the over-voltage. Since electricity takes the shortest path of least resistance, the voltage spike goes through the Varistor, instead of through the entire game's circuit boards. Because the varistor creates a short circuit, the varistor and the line fuse are be damaged in the process. The game will run fine without the varistor, but is no longer protected from voltage surges and spikes.

A fried varistor. (photo by Jean - JMBD).

The Line Filter (small metal box), is used to suppress radio frequencies. House wiring acts like a big antenna picking up television, cell phone, radar, and other signals. These frequencies can interfer with the CPU board. The same thing applies in reverse, and the filter prevents the high frequencies from the game flowing back into the AC circuit.

Cracked Header Pins.
A very common problem on all power supplies from this era is cracked header pins. Microscopic cracks can develop in the header pins soldered to the power supply board from vibration and inserting/removing connectors.

The best way to fix this is to resolder the header pins. NOTE: it is *highly* recommended that the old solder be removed, before adding new solder! This can be done using a solder removal tool, as documented in the document at marvin3m.com/begin. Also look for any damaged or burnt header pins. Replace them now if any are found!

Please refer to this KEY picture to find the components involved in the upgrades mentioned below (this is a system6 power supply board, but this is essentially the same power supply as used on system3 to system7, though system7 power supplies are slightly different). Picture by Mark.

Upgrade 1: Replace Filter Capacitor C15 (C10 on System7).
(Component #3 in the "key" picture.)
This is the +12 and +5 volt logic filter capacitor. Electrolytic capacitors have a working life of about 10 years. So if this capacitor is original, chances are nearly 100% that this capacitor needs to be replaced! On System3 to System6 games, this is a 12,000 mfd 20 volt electrolytic capacitor. On System7 games, this is a 18,000 mfd 20 volt electrolytic cap.

Failure to replace this +5/12 volt filter cap will can cause all sorts of unpredictable game behavior and problems. Game resets and lock ups are most common. THIS CAPACITOR MUST BE REPLACED ON ALL SYSTEM3 TO SYSTEM6 GAMES! Also a darn good idea on system7 games too.

On system3 to system6 power supplies, the +12/+5 volt power is rectified by *two* diodes. This is unlike system7 or just about any other pinball manufacturer which use a bridge rectifier (four diodes) for the 5/12 volt power chain. Using just two diodes gives "half wave" rectification. Using a bridge rectifier with four diodes gives "full wave" rectification. What does this mean? In the case of half wave rectification (two diodes) as used on system3 to system6 power supplies, the filter capactior has to work much harder to give smooth +5 volts. Because of this it is *very* important to have a new +5/12 volt filter capacitor on the power supply board for system3 to system6 games. Any new capacitor in the 10,000 mfd to 18,000 mfd range (16 volts or higher) is fine.

Note on Williams system3 to system7 games with more than two flippers, a higher MFD filter cap will be required! For example any Willams system3 to system7 game with three or four flippers should have a 15,000 MFD filter capacitor. Anything less and the game will reset if both cabinet flipper buttons are pressed at the same time.

Often many techs will measure the amount of AC voltage coming through on the DC 5/12 volt circuit. This is done with a digital multimeter (DMM) set to low AC volts, putting the DMM's leads on the two leads of the 5/12 volt filter capacitor. Normally anything above .200 volts AC means the 5/12 volt filter capacitor is bad. But on system3 to system6 games, because of the two diode half wave rectification, it is nearly impossible to get less than .200 volts AC even with a new filter capacitor. Just keep that in mind. On system7 games a new 15,000 MFD filter cap should put the AC ripple at .100 to .200 volts AC, which is fine.

Note all newer capacitors (of the same value) are smaller than the original capacitor. Original style 15,000 or 18,000 mfd axial electrolytic capacitors are not easy to find. An easier to find replacement, currently available from many sources, are radial "Snap Caps". To install one, the snap cap will need to be siliconed (and if possible nylon tie wrapped) to the power supply board, and have wires going from its terminals to the power supply board. Not the cleanest look, but it does work well. Be sure to mount the cap "flat" to the power supply board, with the cap leads facing *down*. DO NOT MOUNT THE CAP WITH THE LEADS FACING OUT (away from the power supply board). Due to the vibration in pinball machines, the silicone used to secure the cap will eventually fail if the "tall" cap is mounted with the leads facing "out".

Another method is to use a snap cap and drill a hole in the board for the second cap lead. This method is NOT recommended! Again, due to vibration, the solder leads will crack, removing the capacitor from the circuit.

DO NOT mount a snap cap like this to the power supply board! The cap should be mounted "flat" to the power supply instead. But note the wires running to the board's contact points. Mount the cap flat on the board with the contacts facing down and silicone it, instead of having it perpendicular to the board (as shown here).

Upgrade 2: Add Fuses for the Lamp & Solenoid Bridges.
Adding these fuse can is a good idea, and could prevent a fire. This applies to all System3 to System7 games. Please see above for this information.

Upgrade 3: Replace Connector at 3J6.
(Component #10 in the "key" picture.)
Replace the header pins at connector 3J6 on the power supply. This applies to all System3 to System7 games. This is the +5 volt connector, and it needs to be in perfect condition. So just replace this with new .156" header pins before even powering the game on for the first time. It is also recommended that the connector's terminal pins in the plastic housing also be replaced, with new .156" Trifurcon terminal pins.

The power supply connect J6 (top right), which outputs the +5 and +12 volts to the rest of the game. This 15 pin connector needs to be replaced, regardless of its condition. This applies to all System3 to System7 games.

Connector J6 is of major importance. Not just because it is the +5 logic power connector, but also because it handles the +12 volt connection to the CPU board's reset section. There is just *one* pin on J6 that handles this 12 volt connection. If this pin is in bad condition, the game will not run! So it's a good idea to just replace the entire connector 3J6, and be done with it.

Diodes D7 and D8 on System3 to System6 power supplies. Obviously these are a bit under-rated for this usage! Note connector J1 (12 pins) has also taken some abuse. This connector supply power to diodes D7/D8.

Upgrade 4: Replace +5/12 volt Rectifying Diodes D7/D8.
(Component #4 in the "key" picture.)
On System3 to System6 power supplies only, the diodes at D7 and D8 need to be replaced. These two diodes rectify the AC voltage to DC, which is ultimately used for the +12 volts and +5 volts logic. The MR500 diodes are 3 amp diodes, but should be replaced with 6A4 (6 amp, 400 volts) diodes, or 6A2 (6 amp, 200 volts), or even 6A50 (6 amp, 50 volts). Radio Shack sells 6A50 diodes, part number 276-1661. Note on System7 power supplies the AC to DC conversion circuit was beefed up. Diodes D7 and D8 were eliminated, and replaced with a bridge rectifier BR1. A bridge rectifier is essentially a grouped set of four diodes.

The same power supply with diodes D7 and D8 replaced with 6A4 diodes. Also connector J1 was replaced.

Upgrade 5: Replace Display Power Diodes Z2/Z4.
(Components #1 in the "key" picture.)
Power supply zener diodes Z2 and Z4 are 1N4764 diodes, which are 100 volt diodes. These should be replaced with 1N4763 diodes, which are 91 volt diodes on all System3 to System7 power supplies. The reason for this is simple; the 91 volt diodes increase score display life. This decreases the score display voltage from 100 volts to 91 volts, making the score display last a lot longer. Since score diplays are now only made by one manufacturer, it is important to make them last as long as possible. The downside to this modification is the score displays will be a bit dimmer. But the added life of the displays is worth it.

A system3 to system6 power supply and the High Voltage section. The two diodes with the faint blue arrows next to them are Z2/Z4 (1N4763). The diode bands are oriented with the blue lines. Also shown are resistors R2/R5 (660 ohm) and R1/R4 (39k ohms). Note Q1 and Q3 are the high voltage transistors, and can be replaced with MJE1503x equivalents provided the legs are crossed (as discussed below).

Upgrade 6: Replace Power Supply Resistors R2/R5 and R1/R4.
(Components #1 in the "key" picture.)
Williams recommend upgrading resistors R2 and R5 from 680 ohms to 1.2K ohm 1/2 watt resistors for better reliability of the high voltage section. Also it's a good idea to at least check resistors R1 and R4, 39k ohms. Replace as needed with new 39k ohm 1 watt flameproof resistors. This applies to all System3 to System7 power supplies.

Upgrade 7: Check Connector 3J3.
(Component #7 in the "key" picture.)
This is the solenoid power connector on the power supply. Very often this connector is brown. This will cause resistance, and weaker coils. This applies to all System3 to System7 power supplies.

Upgrade 8: (System7) Replace the G.I. Connectors.
(Not shown in the "key" picture.)
Also also applies to the System3's Hot Tip and Lucky Seven. Basically all System7 games will have burnt G.I. (General Illumination) connectors on the power supply board. More information on this is below.

Before turning the game on for the first time, it is a good idea to test the power supply. If any part of the power supply is not working, the rest of the game is not going to work. And a damaged power supply could damage some other component of the game. So it's best to isolate and test the power supply first, before doing anything else.

To do this, disconnect *all* the connectors from the power supply, except for 3J1 and 3J2 (these are the two square connectors). J1 is a rectangle 12 pin connector, which feeds all the input voltages to the power supply. J2 is a rectangle 6 pin connector, which feeds ground from the external bridge rectifiers. All the other .156" straight line connectors are output connectors, and should be removed.

Power supply components shown on a System3 to System6 power supply. Picture by Mark.

1. The +100/-100 volt score display power supply.
2. The +5volt DC regulator for the logic power supply.
3. The 12,000 mfd filter capacitor for the +5 volts logic power.
4. The rectifier diodes for the +5 volts logic power supply.
5. The power input connectors. The larger square Molex connector on the bottom is the power inputs from the transformer and backbox bridge rectifiers. The smaller square connector is the lamp/solenoid bridge rectifier ground input.
6. The filter capacitor for the +28vdc solenoid power supply.
7. Solenoid and Flipper power output connector.
8. Lamp and Solenoid power output connector.
9. Display Power +100/-100 output connector.
10. Logic power output connector (+5 volts regulated and +5 volts unregulated).
11. The +100/-100 rectifying diodes which convert 100 volts AC to unregulated DC.

Check the +12 volts.
With all the connectors removed except for J1 and J2, turn the game on. Measure the +12 volts DC with a DMM at 3J6 pin 6 (pins 11 to 15 of J6 are ground). This is unregulated 12 volts, so it should be in the 10 volts to 14 volts DC range. If the voltage is outside that range, most likely it is the filter capacitor (C15 12,000 mfd at 20 volts for system3 to system6, or C10 18,000 at 20 volts mfd for system7). This capacitor commonly fails on these power supplies. There is more information on this capacitor below (see the +5 Volt Logic Filter Capacitor.)

Beyond the capacitor, on system3 to system6 games, it could be either diodes D7 or D8 (MR500, which should have been replaced with 6A4 diodes, as discussed above). These diodes commonly fail due to heat. These diodes can be easily tested using a DMM set to the diode function. Put the DMM leads on each lead of the diode, and a reading of .4 to .6 volts should be seen in one direction, and no voltage in the other. On system7 games, the BR1 bridge rectifier (35 amps 400 volts) could be faulty. Lastly the problem could be the transformer (but that is unlikely). Testing this bridge rectifier is described below in the +5 volts section.

Check the +5 Volt Logic Voltage.
The +5 volts is the power that runs all the logic circuits on the game. If the +5 volts is not "perfect", the game will not run at all, or will have random resets and lockups. There are two things that make the +5 volts "perfect": voltage in the 4.9 volt DC to 5.2 volt DC range, and a nice "smooth" 5 volts. The +5 volts is not adjustable (the power supply have components that do this automatically).

To check the +5 volts, use a DMM and measure the +5 volts DC at power supply connector 3J6 pins 7 to 10 (remember J6 pins 11 to 15 are ground). The +5 volts should measure between 4.9 and 5.2 volts DC.

If the +5 volts is low at the power supply, either the connectors are in bad shape, or the regulation circuit is probably damaged. If the voltage is Ok at the power supply, but is later tested at the CPU board and found to be less than 4.9 volts, the CPU board could also have some problems that are "dragging down" the power supply. There could also be a problem on the power supply +5 volt regulation circuit, which fails "under load". But first check and replace the connectors on the power supply (3J6) and the CPU board (1J2) before doing anything else.

Fixing a bad +5 volt circuit is pretty straight forward. On System3 to System6 games, this involves the large heat sinked X3 (LM323, 3 amp, 5 volts) voltage regulator on the power supply board, and two diodes at D7 and D8. The voltage regulator itself is pretty well protected and doesn't usually fail. As described above, diodes D7/D8 do often fail though. A shorted D7/D8 diode should blow a fuse, an open diode causes +5V voltage to drop and prevent the game from starting. These can be easily tested using a DMM set to the diode function. Put the DMM leads on each lead of the diode, and a reading of .4 to .6 volts should be seen in one direction, and no voltage in the other.

On System7 power supplies, low or no +5 volts is either the bridge rectifier BR1, chip IC1 (723PC), or transistor Q5 (2N6057, which should be replaced with an easier to get 2N6059). The bridge rectifier BR1 (35 amps 400 volts, which is really four diodes in a metal case) is used to convert AC to DC volts, and replaces the D7/D8 diodes on older System3-6 power supplies.

The System7 BR1 bridge can be tested. Note the positive side of the bridge is "offset" from the other three leads, with the lug facing a different direction than the other three lugs. The negative lug is diagonial to the positive lug. And the two AC lugs are the two remaining lugs.

1. Turn the game off.
2. Put the DMM on diode setting.
3. Put the black lead of the DMM on the "+" (positive) terminal of the bridge.
4. Put the red lead of the DMM on either AC bridge terminal. Between .4 and .6 volts should be seen. Switch the red DMM lead to the other AC bridge terminal, and again .4 to .6 volts should be seen.
5. Put the red lead of the DMM on the "-" (negative) terminal of the bridge.
6. Put the black lead of the DMM on either AC bridge terminal. Between .4 and .6 volts should be seen. Switch the black DMM lead to the other AC bridge terminal, and again .4 to .6 volts should be seen.

Check the High Voltage +/-100 volts.
With all the power supply connectors still removed except for J1 and J2, turn the game on. Put the DMM's black lead on J5 pin 1 (ground). Put the red lead on J5 pin 3, and between -90 to -105 volts DC should be seen. Now move the red DMM lead to J5 pin 4, and +90 to +105 volts DC should be seen. If these value are off, the high voltage section of the power supply will need to be rebuilt (see below).

With the connectors on, if the score displays are dead, before repairing the High Voltage supply, look for a small orange glow in the corner of the score displays. If that is present, then the proper voltages are probably getting to the displays, and the problem lies elsewhere, other than the high voltage section.

If the score displays light up, but then go dim or flicker, try replacing the two 100 mfd 150 volt electrolytic filter capacitors in the high voltage section (C7/C11 on System3-6, C1/C3 on System7). When those capacitors dry up and get old, the displays can look like they are dying.

Also part of the high voltage section on the first two System3 games (Hot Tip and Lucky Seven) is a 300 volt supply circuit. The original design used this voltage to provide an extra "kick" to get the score displays gas to ionize. Hot Tip and Lucky Seven used this extra voltage, but it was deemed unnecessary after that and dropped. If a System3 power supply has some extra capacitors and diodes that aren't on the schematic, this is part of the 300 volt supply. The 300 volts was produced using two diodes and two capacitors to triple the incoming AC voltage. If a System3 power supply has a failed 300 volt supply, there is no need to repair it. The two extra diodes and capacitor can be removed, and this will not affect the score displays.

Check the Lamp Voltage.
With all the power supply connectors still removed except for J1 and J2, turn the game on. Put the DMM's black lead on J4 pin 1 (ground). Put the red lead on J4 pin 5 to pin 8, and between 16 to 20 volts DC should be seen. If this voltage is missing, a fuse is probably blown, the connector is bad, or the backbox 6BR1 bridge rectifier has failed (or the connectors going to this bridge have come off, which is common, see below). Also note the large "can" capacitor in the bottom of the backbox *not* mounted on the power supply is used to smooth this lamp voltage. Sometimes this 30,000 mfd 25 volt capacitor fails too (though this is rare).

Check the Solenoid Voltage.
With all the power supply connectors still removed except for J1 and J2, turn the game on. Put the DMM's black lead on J3 pin 3 (ground). Put the red lead on J3 pin 6 to pin 9, and between 28 to 38 volts DC should be seen. If this voltage is missing, a fuse is probably blown, the connector is bad, or the backbox 6BR2 bridge rectifier has failed (or the connectors going to this bridge have come off, which is common, see below). On the Power Supply board there is also a 47 volt varistor, used to protect the solenoids from voltage spikes. There is also a 100uf filter capacitor.

The flipper voltage has a slight deviation. On System3 and System4 games, +28 volts goes directly to the flippers from the solenoid bridge rectifier (there is a fuse located under the playfield). On System6 and System7 games, the flipper voltage is goes through the Power Supply board (but is not manipulated), with fuse F4 protecting the flipper circuit (the under playfield fuse is now gone). On the last three System7 games (Firepower2, LaserCue, Starlight), flipper power comes from a separate 50 volt flipper power supply board.

The +5 Volt Logic Filter Capacitor - Replace it Now!
The last piece of the +5 volt logic puzzle, and the one that fails often, is the filter capacitor. After the voltage is converted from AC to DC, the voltage must be "smoothed". This is done using a large capacitor (C10 on System7 power supplies, C15 on system3 to system6 power supplies). Originally the value of this capacitor was 12,000 mfd at 20 volt.

Filter caps are largely a mechanical device. Because of this, they wear out! The normal life span for a filter cap is about 10 years. Since these games are well past that age, I would highly recommend replacing this capacitor! On system3 to system6 power supplies, it is really important to replace it because of the lower value Williams used. System7 power supplies have less problems with this cap, but it is still a good idea to replace it.

The capacitor can be tested, with the game on using a DMM set to AC voltage. Put the red lead of the DMM on the positive lead of the filter capacitor, and the black lead on the negative lead of the cap. If an AC voltage of .300 volts AC or more is seen, the capacitor is not smoothing the DC voltage enough, and definately needs to be replaced! Unfortunately on system3 to system6 power supplies that use just *two* diodes for (half wave) rectification, even with a new 5/12 volt filter cap, never less than .200 volts AC will ever be seen. On system7 power supplies this was change to a bridge rectifier (four diodes) for "full wave" rectification. A new filter capacitor on system7 power supplies should not show more than .100 volts AC.

Problems with the Backbox Mounted Bridge Rectifiers Wire Lugs.
One of the first things to check on these games is the two bridge rectifiers mounted on the rear wall of the backbox. These bridges are used for the solenoids and lamp matrix power. The connectors used to attach the wires to the terminals of these bridges are sometimes loose, causing playfield lamps to go out, solenoids to be weak or intermittent, and fuses to blow. Tighten the connectors with pliers and reseat them, or just solder the wires directly onto the terminals.

Williams CPU Board System 6 Test Points and their Location.
Note there are no test points on system3 and system4 CPU boards.

• TP1 = +12 VDC unreg. (upper left)
• TP2 = NMI, +5 VDC (upper left, up and right of TP1) It should read 0 VDC when diagnostic switch SW1 is pressed.
• TP3 = Memory Protect (upper center) +5 VDC when interlock closed, 0 VDC when interlock open.
• TP4 = Blanking (left middle) +5 VDC normal operation, 0 VDC blanking (when first turned on for about 1 second).
• TP5 = IRQ (lower left of center)
• TP6 = Phi 2 (lower and left of TP5)
• TP7 = CMOS RAM B+ (lower center) +4.3 VDC when power on, +3.9 VDC when power is off. If this is low, your batteries are low.
• TP8 = RESET (lower left corner of batteries) 0 VDC for first second that power is on, +5 VDC after that.
• TP9 = +5 VDC (lower right)
• TP10 = Ground (lower right)

A Revision System6 board has a part number on the lower right corner ending in a 6 or 6A, or something similar. If the board in question does not match the location of the test points, or if the part number differs, it may be a system7 CPU board, as the test point location differs (see below).

Williams CPU Board System 7 Test Points and their Location. The system7 test points are the same as system6, but their location is different.

• TP1 = +12 VDC unreg. (upper left)
• TP2 = NMI, +5 VDC (center bottom) It should read 0 VDC when diagnostic switch SW1 is pressed.
• TP3 = Memory Protect (left center) +5 VDC when interlock closed, 0 VDC when interlock open.
• TP4 = Blanking (left bottom, just to right of batteries) +5 VDC normal operation, 0 VDC blanking (when first turned on for about 1 second).
• TP5 = IRQ (near upper right side)
• TP6 = Phi 2 (lower right side)
• TP7 = CMOS RAM B+ (just under TP3) +4.3 VDC when power on, +3.9 VDC when power is off. If this is low, your batteries are low.
• TP8 = RESET (right bottom) 0 VDC for first second that power is on, +5 VDC after that.
• TP9 = +5 VDC (lower left, just at the upper right corner of batteries)
• TP10 = Ground (lower left, next to TP9)

Remember some early Black Knight games (first system7 game) used the early System6 power supply. This is easy to identify; if the transformer is in the lower cabinet, it's a system7 power supply. If the transformer is in the backbox, it's a system6 power supply. A System7 CPU board has identical test point values to a System6 board, but the test points are in different locations.

The additional power supply .22mfd caps only needed for Hot Tip and Lucky Seven. Pic by Karonhalt.

Additional Power Supply Parts on System3 Hot Tip/Lucky Seven.
The first two system3 games (Hot Tip and Lucky Seven) had two additional capacitors and diodes compared to the later system3 to system6 power supplies. These were used for the 300 volt feed for the display driver. These parts were dropped starting with World Cup (the third System3 game). Unless there is a specific problem with the display drive on these two games, the two 1N4001 diodes and two .22 mfd capacitors do not need to be replaced or checked (the capacitors are actually not electrolytics, but are "MKP" caps). They can even be removed entirely from the power supply if used in later system3 to system6 games.

A system3 to system6 power supply and the High Voltage section. The two diodes with the faint blue arrows next to them are Z2/Z4 (1N4763). The diode bands are oriented with the blue lines. Also shown are resistors R2/R5 (660 ohm) and R1/R4 (39k ohms). Note Q1 and Q3 are the high voltage transistors, and can be replaced with MJE1503x equivalents provided the legs are crossed (as discussed below).

Rebuilding the +/- 100 volt High Voltage Section.
Williams used two different types of transistors, and slightly different circuitry routing, for the display power supply circuitry on their games from 1977 through 1989.

Commonly Defective System3 to System6 High Voltage Parts:

• Q1 = MJE15030* (NTE54) - replaces the original SDS-201 (NTE171).
• Q3 = MJE15031* (NTE55) - replaces the original SDS-202 (NTE296).
• Q2 = MPSD52 (NTE288, 2N5400, or 2N5401).
• Q4 = MPSD02 (NTE287, MPS-A06, or MPS-A42).
• Z2,Z4 = 1N4763 (91 volt) zener diodes - replaces the original 1N4764 (100 volt) diodes.
• Z1,Z3 = 1N4730 (3.9 volt 1 watt) resistors - replaces the original 1N5990 (3.9 volt 1/2 watt).
• R2,R5 = 1.2k ohm 1/2 watt resistors - replaces the original 680 ohm 1/2 watt resistor.
• R1,R4 = replace with 39k ohm 2 watt - replaces the original 1/2 watt version.
• C7,C11 (C1,C3 on System7)= 100 mfd 150 volt electrolytic capacitors.

* Note that the original style SDS201/SDS202 transistors at Q1/Q3 are no longer available in any flavor or form. These two transistors must be replaced with the newer MJE15030/MJE15031 transistors. BUT NOTE: the MJE transistors had a different pinout than the original SDS transistors, so they must be installed differently on the board!!

Pinouts:

• SDS trans: E B C
• MJE trans: B C E

A replacement MJE15031 in an older System6 power supply. The leads on the MJE15030 and MJE15031 must be "twisted" to replace the older SDS201 and SDS202 transistors. IMPORTANT: heat shrink tubing should be installed over the crossed leg to prevent shorts!

The MJE transistors can also be installed without any board moficiations, but this can be a bit difficult. The left two legs must be installed in the 2nd and 3rd holes, respectively (as described above), and the rightmost leg will then criss-cross under the first two legs, and install in the 1st hole. This is actually the way Williams recommended doing it in their service bulletin. It is recommened that some heat shrink tubing be installed on the rightmost leg to prevent any arcing or shorts to the other legs.

How old are those batteries in that game? If an answer can not be determined, it's time to change them! Besides dead batteries, CPU board battery corrosion and/or a bad IC19 CMOS 5101 RAM can cause some problems too. This section talks about these problems.

The problem with old batteries is leakage. If the batteries leak, they will leak corrosive material over the CPU and driver board! Also the corrosive fumes from the batteries alone can corrode the ROM sockets and the 40 pin inter-board connector. This is cause random game lock ups and resets, game boots into audit mode, or make the game not work at all.

Isn't Battery Corrosion Obvious?
The short answer is, "no!" Batteries can leak corrosive fumes, which may not corrode the circuit board. But these fumes can corrode sockets and header pins without it being obvious. If these pins get even gray, it can increase the resistance of the pin, or make the pin not conduct at all. It can even make an internal socket pin break, which may not be seen by the naked eye. And this in turn can make a game not work. Any grey/green pins of a socket or header pin is probably from leaking battery fumes.

Battery corrosion just under the battery holder shorted address line A10 to chip select CS1. This short made the CPU board not boot. Picture by Jerry.