(material and photos copyright 2002 Mark Orthner unless otherwise noted)

For a short while I had titled this guide "Zen and the art of troubleshooting early Williams SS games".  I was a bit too cute for my taste (like the logo isn't!), but I still like my original reason for the title: "Why the title?  Years ago I read the following definition of Zen: "Zen stresses the importance of the enlightenment experience and the futility of rational thought...".  Well, if you have ever spent time troubleshooting a System 3 game, then you know that rational thought has nothing to do with the process and the only way that game is going to get working is through some divine enlightenment!"

I started work on this guide because there were no other resources available on the Internet devoted to early Williams Solid State games.  These games range from "Hot Tip", released late in 1977, to Laser Cue, released in early 1984.  Over 150,000 games were produced in this series, rivaling both the System 11 and WPC eras. 

Unlike early Bally and Gottlieb games, there are no "replacement" boards available for the early Williams games, so knowing how to repair the electronics on these games is a must if one is going to collect this era of game. 

The majority of the information in this guide is the direct results of my experiences in repair and maintenance of my collection of System 3 through 7 games (I've owned 16 different titles so far). I learned through trial and error and also through exhaustive searches of Internet archives (http://groups.google.com in the rec.games.pinball newsgroup archives).  Several of the prolific posters who deserve mention are Ray Johnson, Clive Jones, John Robertson, David Gersic and Duncan Brown.  I would also like to thank to Frank-Rainer Grahl for reviewing the "time-line" and providing updates on intra-system compatibility.  The tests documented in this guide are the result of the fabulous work of Leon Borré.  Ted Estes contributed some great background information on Firepower and some of the early design decisions.  



Part 2, "Connectors and other intermittent problems" can be found here
Part 3, "Getting the Power" can be found here
Part 4, "MPU Board Troubleshooting" can be found here
Part 5, "Driver Board Troubleshooting" can be found here

Part 1 - Introduction to the Williams Solid State Pinball Machine

1. Understanding the Williams Solid State Pinball Machine

Before attempting to troubleshoot an early Williams Solid State Pinball machine, a good understanding of the major components and their corresponding functions is essential.  The majority of repairs can be accomplished by the average hobbyist as long as you know what you're looking at.  You can cause more damage to your machine by idly poking a prodding around in a vain attempt to "repair" without a good working knowledge of what everything does. 

1.1 A Brief History and the Evolution of the Williams Solid State Machines

Williams introduced its first Solid State pinball machine in late 1977.  The machine was "Hot Tip" and was also released in an electro-mechanical version.  All Williams Solid State games from Hot Tip in 1977 up to Laser Cue in 1984 shared the same basic design architecture. In 1981 Williams made some major revisions to the MPU board (System 7 board), but the overall architecture remained the same.  In 1984 Williams introduced the System 9 board which combined a majority of the functions onto a single board.

As you can tell by the preceding paragraph, early Williams Solid State games are referred to by the revision number of the CPU.  Along with CPU revisions, other revisions were made along the way to the sound boards, displays and display drivers and power supplies.  At times it can be daunting 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:

  • System 3 - Introduced in 1977 with "Hot Tip", the System 3 board was Williams first production Solid State system.  Hot Tip and the second Solid State game, "Lucky Seven", did not have electronic sound, but still relied on electro-mechanical chimes.  Electronic Sound was introduced in 1978 with "World Cup".

    (System 3 MPU, click on photo for larger image, picture will open in a new window)

    System 3 games include Hot Tip (also released in an electro-mechanical format), Lucky Seven (also released in a two player electro-mechanical format), World Cup, Contact and Disco Fever.

  • System 4 - The System 4 board was introduced in 1978 with "Phoenix" and incorporated several minor enhancements to the clock and reset circuits.  With Flash in 1979, Williams introduced the concept of "continuous" background sound (and a corresponding new sound card).

    (System 4 MPU, click on photo for larger image)

    System 4 games include Phoenix, Pokerino, Stellar Wars and Flash.

  • System 6 - The System 6 board was introduced in mid 1979 during the production run of "Flash".  Quite a few major internal enhancements were made on this board, including the addition of memory protection and the use of the 6808 processor with its onboard clock.  It was the most widely produced Williams MPU board every, with almost 100,000 units manufactured.  Williams introduced speech into the Pinball World in 1979 with "Gorgar" and its seven word vocabulary.

    (click on photo for larger image)

    System 6 games include Flash (end of production run), Tri-Zone, Time Warp, Gorgar, and Laserball.

  • System 6a - A minor revision was made in the System 6 board around the time of the release of Firepower.  The data buffer chips IC9 and IC10 were removed.

    * The last two System 6 games, Algar and Alien Poker used 7 digit displays.

    Games shipped with System 6a boards include Firepower, Blackout, Scorpion, Algar and Alien Poker.

  • System 7 - The System 7 board was introduced in late 1980 with "Black Knight".  To the casual observer, a System 7 game could be identified by its use of 7 digit displays.  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 System 7 board, however it required some soldering (jumper changes) on the board or ROM revisions to allow it to work in earlier games (you don't need to do that however, see my ROM page for details on running System 7 boards in all System 3 to 6 games!).  Later System 7 games switched from a 28 volt Flipper coil to a 50 volt Flipper coil, adding an additional power supply and transformer to the game.

    (click on photo for larger image)

    The major System 7 games were Black Knight, Jungle Lord, Pharaoh, Solar Fire, Barracora, Firepower, Cosmic Gunfight, Firepower II and Laser Cue.

    Williams produced System 7 games in very limited quantities, few of which still exist today.  Varkon (90), Thunderball (10), Defender (350), Time Fantasy (600), Warlock (400), Joust (400).

    I'm not sure whether it was the recession or the video game revolution, but Williams produced less than 3,000 pinball games in 1982 and 1983 combined after having produced over 75,000! pinball games in 1981 and 1982.

  • System 9 - 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 MPU, Driver and Sound boards was replaced with a single board.  Externally, a casual player wouldn't notice any difference between a System 7 and System 9 game as they both used 7 digit numeric displays.  

  • System 11 - The System 11 board was introduced in 1985 with High Speed.  It was also a "combined" board with CPU, driver and sound all located on the same board.  System 11 games used both alpha-numeric and numeric displays.  Later System 11 games used only alpha-numeric displays.  The System 11 board went through 4 revisions and the boards were given "dash" suffixes, i.e., System 11a, System 11b.  

  • WPC - The WPC System, "Williams Pinball Controller", was introduced in 1991 with Funhouse  These games featured Dot Matrix Displays (DMDs) (although Funhouse still utilized alpha-numeric displays).  An interesting note is that Williams switched back to separate MPU and Driver boards with the WPC System.

  • WPC95 - Williams caught Microsoft's naming bug in 1995 with the release of the WPC95 system.  

  • Pinball 2000 - Continuing with the Microsoft naming convention, Williams introduced Pinball 2000 in 1999 with "Revenge from Mars".  A hybrid video-pinball system that introduced a 3-dimensional "virtual" playfield, only 2 Pinball 2000 titles were produced before Williams pulled out of pinball manufacturing in October of 1999.

1.2 So what works with what?  Here is a brief rule of thumb for part compatibility between Williams Solid State games:

  • System 3 through 6 games share the most compatibility.  They all use the same driver board, displays and display driver.  The MPU boards are backwards compatible, in that you can use a System 6 board from a Time Warp in a Hot Tip. 
  • Early power supplies also contained a 300 volt feed for the display driver that was later dropped.  You can use the power supplies interchangeably between system 3 and 6 games.  System 7 power supplies were redesigned with the GI circuit being added back in. You can use a System 7 power supply in a System 4-6 game.  There will be three connectors that are not used and you will need to add a fuse to F4 for System 6 games.  

  • Transformers on earlier games also used slightly different plug arrangements.  System 3 games routed the GI power through the power supply board while later games had direct connections to the fuse block for the GI circuit.  If you are swapping transformers, make sure you have the GI power routed properly.  System 7 game transformers are also compatible with earlier games.  Because they were mounted in the cabinet, they will have a connector on the +28 and +18 volt secondary outputs.  This just needs to be cut off to use the transformer in a System 3-6 game.

  • Williams used three different sound boards in these systems, and they are specific to certain games.  World Cup through Pokerino share the same card, then Flash through Scorpion, and finally Gorgar through Alien Poker. 

  • System 7 games use a slightly modified Driver board.  8 resistors in the switch matrix were replaced with jumpers.  A common misconception is that driver boards are backwards compatible between System 7 and System 3-6 games.  NOT TRUE! Using a jumpered System 7 driver board in a System 6 game may result in random switch closures during game play.  Using a System 3-6 game in a System 7 game will result in switch closures being missed.  USE THE RIGHT DRIVER BOARD FOR YOUR GAME!

  • System 7 MPU boards can be used in System 4 to 6 games.  System 3 games (games using the White Flipper ROMs) can be run on System 7 boards, however you will need to accept the "factory" settings since most System 7 boards lack the DIP switches required to program the options.   There are two ways to run the software on a System 7 board.  The first requires a series of jumper changes (soldering required), the second is to used a "doubled up" Flipper ROM and the existing game ROM.  This method requires no jumper changes.  You can get the new Flipper ROMs here. 

    Early System 7 boards did have dip switches and LEDs (see below) and the ability to accept adjustment programming via the dip switches.

  • System 9 games share the same power supplies (main and flipper) and displays with System 7 games.  Although the display driver board is the same design electronically, Williams switched from edge connectors to plug connectors on some System 9 display driver boards.  The speech boards may also look the same, but System 9 speech boards are designed to use 2732 EPROMs, while System 6 and 7 speech boards use 2532 EPROMs, so the two are not compatible without a jumper change.

  • No System 11 or later parts, other than 7 digit numeric displays, are plug compatible with earlier games.  However, I have been told that a System 11 board can be used in a System 9 game!  System 11 power supplies can be used in older games if a modification is made to the GI circuit.

1.3  Williams System 3 through 7 Design Architecture

All Williams System 3 through 6 games share the same design architecture.  For the most part, System 7 games do also, albeit 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, in that the MPU 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 these boards were designed is that the driver boards were much more likely to fail than the MPU 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 MPU board, then no ROM swap would be necessary for the majority of repairs.

This philosophy actually held true, as driver boards have proven much more likely to fail then the MPU.  What Williams and the other manufacturers didn't bargain for however was the failure of the connectors between the driver and MPU boards.  Gottlieb had the worse problem 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 interconnection.  This requires the pins to provide high speed data transfer, where as dirt and loose connectors can bring the game to a halt.

All games share the same five major components, the MPU (or CPU) board, the Driver board, the power supply, the display driver and the displays.  All games after Lucky Seven also had a sound board, and later System 6 games and early System 7uch as Gorgar, Blackout, Firepower and Black Knight had speech boards.

For reasons unknown, all System 3 and most System 4 games had their sound boards located in the cabinet, while later System 4 games and System 6 and 7 games had their sound boards located in the back box.

Inside of a typical Williams System 6 back box:

MPU Board

Williams calls its CPU boards, "MPU" boards (just to be different I guess!).  The MPU board contains the microprocessor, diagnostic and display logic.  Williams games were designed around the Motorola 6800 series of chips.  Also contained on the MPU board are the game's ROM (Read-Only Memory) chips that contain the game specific program.  The diagnostics on a Williams MPU board consists of two LEDs.  A common mis-conception is that Williams boards do a "self-test" like the boards from other manufacturers.  In reality, a self-test only occurs when you press the test button.  

Driver Board

The Driver board in early Williams Solid State games is actually an extension of the MPU board.  The Driver board controls the solenoids and lamps and reads the switches. The 6808 microprocessor used in these games communicates to the "outside" world (the game in this case) through the use of what are known as "PIA" chips.  PIA stands for "Peripheral Interface Adapter".  These chips have the designation 6821, however early driver boards may have used 6820 chips (which can be replaced with 6821 chips)  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 down and it "writes" to the PIA to fire a solenoid or change the score.

Games through System 6 games used four PIA chips.  One on the MPU board to control the displays and three on the Driver board.  One 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 MPU board will not "boot" without the driver board installed.  There are special diagnostic chips available that will allow you to test the MPU board with the driver board detached.

System 7 games have an additional PIA on the MPU board that is used to drive the Sound Board.  This leaves more driver board solenoid connections available for playfield coils.

The PIA chips are easily identifiable, as they are the large 40 pin chips on the board.  Don't worry if your chips don't say 6821 on them.  Williams bought these chips in large quantities which were manufactured specially for them and they have a proprietary designation on them. 

The electrical current used in a pinball game would fry a 6821 in a nano-second!  To prevent this a series of IC (integrated circuit) chips and transistors are used in between the PIAs and the rest of the game.  The ICs also provide other controls which will be discussed later.

Power Supply

I think the power supply is one of the most misunderstood parts of the game.  There are actually multiple independent power circuits in the game.  People will replace parts of one circuit thinking they are fixing another.

All games through System 7 have the following power circuits:
   +5volt regulated DC "logic" power 
   +12 volt unregulated DC
   +100 and -100 volt DC display power
   +28 volt solenoid and flipper power 
   +15 volt lamp power
   6 volt AC GI (General Illumination) lamp supply

The two bridge rectifiers bolted to the backbox are for Solenoid and Lamp 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 power supply only.

Another often confused area is the value of the +12 volt unregulated power circuit.  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.  This voltage is monitored by the MPU board to determine when you've turned off the power so it can shut down things like the displays so they're not damaged during power down.  People will attempt to "repair" their power supplies because they're not getting 12 volts, only 11 volts.

Later System 7 games used 50 volt flipper coils and had an additional "flipper" power supply board (and an additional transformer in the cabinet).

Sound Board

The first two Williams Solid State games, Hot Tip and Lucky Seven, continued to use "chimes" like the electro-mechanical games.  Hot Tip also had a "dummy" score reel in the cabinet that would be incremented to make the familiar scoring sound. World Cup was the first Williams game to use electronic sound.  Sound boards are actually self-contained computers, complete with their own power supply, microprocessor and PIA.  The game "sees" the sound board as a set of solenoids, using the same controls on the driver board to trigger different sounds as it would to fire a solenoid.

Games from World Cup to Pokerino used a sound board that would generate a sound when an activity occurred (scoring, etc.).  However when the ball wasn't hitting anything, no sound was being produced.  Starting with Flash, 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 introduced speech to the pinball world. A redesigned sound board featured a connector for an add-on speech module.  Speech was featured on Gorgar, Firepower, Blackout, Alien Poker, Black Knight, Jungle Lord and Pharaoh.  The recession of the early 80s that almost drove Williams out of business caused major cost cutting moves in pinball production, and speech was eliminated from all System 7 games after Pharaoh.  The sound board in these later games is missing the connector that was used to connect the ribbon cable from the speech board to the sound board, showing how far they went in reducing production costs.


Williams used a standard 6 digit gas filled display in all its games through Algar.  These are still widely available today.  Most 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.  The last two System 6 games (Algar and Alien Poker) use 7 digit displays  and all System 7 games used a 7 digit display.

Display Driver

The display driver is mounted just behind the backglass on the front of the display panel.  The display driver also contains the credit/match display.  The job of the display driver is to take the binary score data coming from the MPU board and translate into the signals understood by the displays.

There were two versions of the display driver manufactured, and both are compatible in all games.  One uses "discreet" components (meaning a large number of individual transistors) and the other uses integrated circuits.  The reason for this is that the UDN6184 "segment driver" chip that Williams used became very short in supply.  Williams designed an alternate board that replaced the functionality of the UDN6184 with individual transistors.  The UDN6184 chip continues to be in short supply today, and averages between $15 and $20 a piece. 

Display board from a System 6 game showing the 4 score displays and the combination display driver/credit match display unit:

Go to Section 2, "Connectors and other Intermittent Problems"

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