Williams System 3 - 7

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Click to go back to the Williams solid state repair guides.

1 Introduction

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

1.1 Game Revisions

System 1 is considered to be the Solid State version of Grand Prix. It is thought that about 5 Grand Prix EM games were converted to SS prototypes using the new System 1 MPU Board and digital displays. The computer was only used for accumulating and displaying the player scores.

IPDB links: Grand Prix SS version          Grand Prix EM version

System 2 was next, with a 10 unit run of another 1976 EM game called Aztec. A working SS is version is very rare. Both System 1 & 2 occurred quickly after each other at the end of 1976. Aztec SS was still a hybrid machine retaining the EM chime unit in the cabinet and a credit window with an EM numbered reel behind the backglass). Player scoring was still the only digital function at that time.

IPDB links: Aztec SS version          Aztec EM version

System 3 games were the first Williams SS production games, starting with Hot Tip in Nov. '77 and ending with Disco Fever in Aug '78. There were based on the Motorola 6800 8-bit CPU and using a Motorola 6820 PIA (Peripheral Interface Adaptor) to handle the Display I/O from the MPU board. They also had three other 6820 PIAs on the Driver Board reading targets and other Switches as inputs and controlling the insert Lamps and Solenoid as outputs. Solenoid drives were mainly used for ball handling by firing coils, with a few triggering sound calls or a 'start of game' tune. So this was the start of WIlliams using computers for game rules and settings. At this point they designed an 8x8 Switch Matrix an 8x8 Lamp Matrix and a Solenoid bank switched by darlington transistors which remained virtually unchanged to the end of Williams System 7.

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

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

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

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

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

IPDB link: Complete System 7 Game list

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

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

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

1.2 Games

1.2.1 System 3

1.2.2 System 4

1.2.3 System 6

1.2.4 System 6A

1.2.5 System 7

2 Technical Info

3 System 3-7 Board Set

3.1 System 3 Architecture

System 3 Technical information goes here.

System 3 was a major step by Williams to digital pinball games. It ushered in the Solid State machines, but to begin with there were problems with acceptance of the new machines.

Williams had the Driver board firing the solenoids on Chime units on the first two System 3 games, and even had a device called a 'noisemaker' (an EM score reel mounted in the body of the game) to provide the sounds of the score reels clicking over! This gave the player the familiar sounds of EM machines which were still around, The player's scoring, their credits remaining and the ball-in-play were all digital and being displayed on the seven-segment gas plasma displays.

Even once they dropped the chimes and 'noisemaker' (for World Cup in May 1978) and added a digital sound board, the operator could still select the more familiar 'bings & bongs'. A switch was provided on the sound board which allowed selection of simple digital chimes. This option persisted right through on System 3 to System 7 sound boards, but for the most part was not used. Digital sound became more popular as time went on.

The design of System 3 was based on the 6808 CPU and what has become a standard arcade peripheral I/O device, the 6821 PIA (originally the 6820). The PIA (or Peripheral Interface Adapter) on the MPU boards was used to drive the display I/O. The driverboard used another 3 x 6820/6821 PIA chips to drive:

  • an 8x8 Matrix for the Lamps
  • an 8x8 Matrix for the Switches
  • and the last PIA drove the Solenoids

More properly the PIAs were used to drive transistors that then accomplished the output tasks. In the case of the Solenoids, darlington transistors were used as an electionic 'relay' to ground coils and fire them. Usually this was used for ball movement, but as mentioned before solenoids could also be used to sound chimes and for other tasks as needed.

The electronic design choices Williams made became the basis for all the digital Bally / Wiliams pinball games and even games being made today. The CPU chips and PIAs may change, more memory and ROM space is available to the programmers, Mosfets are used as the switching relays instead of Transistor... yet the basic designs for the Lamp Matrix, Switch Matrix and firing of the Solenoids remain unchanged.

3.2 System 4 Architecture

System 4 Technical information goes here.

The System 4 architecture is little changed from the previous System 3 generation. The only functional changes from System 3 to System 4 was a minor alteration to the reset circuit as well as minor changes to the data and address bus in order to more easily facilitate the use of larger EPROMS for the game specific programming.

System 4 machines began with Pokerino in 1978 and ended with Flash in 1979. Late production Flash machines also utilized the then-new System 6 boardest in place of System 4.

3.3 System 6 Architecture

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

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

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

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

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

The 6802 processor was the same architecture and 'backwards compatible' with the 6808, but had internal RAM, instead of the 128 x 8 bit MC6810 at IC13 which must be used with the 6808 CPU. Pin 36 is usually grounded on the 6808, and you can therefore use a 6802 on older boards and it will work, provided the external 6810 RAM is good. If you set Pin 36 of the 6802 "high" (usually through a 4.7K "pull up" resistor to the +5v logic rail) then the internal RAM is enabled. The 6810 (if not socketed) can usually be left in place. On System 6(a) boards, this is accomplished easily by removing jumper J1 and adding a 4.7K resistor at R4.

3.4 System 7 Architecture

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

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

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

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

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

3.5 Flipper ROMs

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

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

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

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

3.5.1 Flipper ROM Colors

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

3.5.2 White Flipper ROMs

Mainly for System 3 games.

3.5.2.1 Exceptions

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

3.5.3 Yellow Flipper ROMs

Used in System 4 games.

3.5.3.1 Exceptions

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

3.5.4 Green Flipper ROMs

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

3.5.4.1 Exceptions

There is an upgraded rom 2 written by Ted Estes that allows /10 scoring in all 6 digit Green rom games. It is probable although unknown if ever tested that this rom in a 7 digit 6a game (Alien Poker/Algar) set to /10 scoring will allow 8 digit scoring, as the 7 digit scoring for those games was an extension contained wholly in the game rom, not in the operating system roms.

3.5.5 Blue Flipper ROMs

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

3.5.5.1 Exceptions

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

4 Problems and Fixes

4.1 Backbox Overview

The WIlliams backbox is similar for most of the games in the System 3-7 games. System 7 was the biggest step change, System 3-6 are very similar in their Backbox layouts.

  • During the beginning of System 7 the transformer moved to the bottom cabinet,
  • The System 7 PSU was redesigned and changed to incorporate a G.I. relay,
  • An upgraded System 7 MPU (or CPU) Board was used.

Some games do not use the optional speech board, early games had no sound boards in the backbox at all! Other than that many of the components and connections were standard and so we will use the System 6 backbox boards as a baseline. Here is a document that shows the System 6 backbox and components in detail, and will help you become familiar with them: System 6 Backbox Wiring Diagram

4.2 Relocating the batteries away from the MPU board

Relocating the 3xAA batteries from the MPU board is always a good idea. Leaky alkaline batteries are the #1 killer of pinball boards. Sometimes the battery terminals don't look corroded, but the metal rivet which contacts the battery are actually missing.

If you see "04 00" in the credit/match display, rather than your game going into attract mode then you are in audits:

  • The batteries have failed and need replacing
  • The battery voltage is not reaching the 5101 CMOS RAM (check Test Point TP7, which should measure 4.3v with the power on and 3.9v (or so) with the power off.
  • Blocking Diode D18 (1N5817) has shorted, and the batteries are trying to run the MPU board when the game is off.
  • You have another problem holding settings, such as a faulty 5101 CMOS RAM.

Simply removing the batteries is not really an option as the game will not boot directly into "attract mode" when switched on. It also will not retain the settings such as the number of balls per game, the free play setting (usually obtained by setting maximum credits to 0) or high scores. If you don't mind always getting default settings, then it's possible on System 3-7 games to switch them off, and then quickly back on to go from the '04 00 audit mode' to attract mode. You would still need to add credits from the coin door, and change settings as needed before starting a game. Too much trouble in my opinion.

Your best option is to remotely locate the battery holder somewhere below all the other boards. This ensures that even if the remotely located batteries leak, they won't leak onto (or even drip onto) any circuit board (see driver board pic below). Use good quality alkaline batteries, mark the date of replacement with a Sharpie, and replace the batteries annually.

Adding a connector between the battery pack and the MPU board is a good idea. You can easily remove the battery pack from the board. Plus, it the batteries are forgotten, and do leak, the MPU board will not have to be removed to add another battery pack. Another solution is to buy a battery holder with the 'transistor radio' type connector which can be snapped on and off. Just be very careful if using this style of connector. Adding a tag noting that a 9 volt battery should never be connected is a very good idea. A 3 x AA battery holder is the typical recommended replacement. If you can only find a 4 x AA battery holder, you can solder a jumper in the first position. Likewise, a diode can be placed in this position instead. This will prevent the batteries from being charged and 'cooked' by the game if blocking diode D17 on the MPU board fails. Keep in mind that an added secondary diode to this circuit will decrease the voltage passing to the 5101, if D17 is still good. Locate a 1n4001 or 1N4004 diode in the position closest to the last + terminal (where the Red Wire exits). You must have the banded side of the diode pointing in the direction of current flow, which is towards the Red wire and towards the (+) terminal marking on the MPU board.

The game takes 3 x AA Batteries, so it uses at least 4.5v total. However, it will still store settings down to about 3v or so. After that an AA battery's life will taper off very quickly. A fresh set of batteries should last for at least a year, or the is some other issue. If the 5101 CMOS RAM is socketed, it's possible that it isn't the low power version. Or, possibly the D17 diode has shorted.

You can see the pictures on the left for how to install the wiring for battery packs to the MPU Boards, if you right-click on the image you can open it in a new tab and enlarge the view.

Williams System 7 MPU Board



On the System 7 MPU, solder the battery cables: Ground (Black Wire) to the Bottom Left pad and Positive (Red Wire) to the Top Right.

Williams System 6 MPU Board



On the System 6(a) MPU, solder the battery cables: Ground (Black Wire) to the Top Right pad and Positive (Red Wire) to the Bottom Left.

Williams System 4 MPU Board



On the System 4 MPU, solder the battery cables: Ground (Black Wire) to the Bottom Left pad and Positive (Red Wire) to the Top Right.

After adding a remote battery pack, and while the board is still out of the game, it is a good practice to measure the battery pack's voltage at the (+) and (-) pads of the MPU board. All battery packs are pretty cheaply made, and failures "out of the box" are somewhat common. Checking to make certain the battery pack is functioning before reinstalling the MPU board in the game will save you some headaches.

Another good practice, while the MPU board is already out, is to check the D17 blocking diode. An open blocking diode will not allow the battery pack voltage to pass through to the 5101 non-volatile memory, and the newly installed battery pack will be ineffective. Conversely, a shorted blocking diode will allow the board's +5vdc logic power bus to pass through to the battery pack. This in turn, will charge the batteries, while the game is turned on. If you're unaware, alkaline batteries do not like being charged. They will heat up, and fail prematurely, (rather quickly). In worse cases, the new batteries can even leak or explode if charged. Testing the D17 diode is quick and easy, and worth the trouble checking it out. When in doubt, replace the D17 diode with a 1N4148, or add a secondary 1N4004 to the battery pack. Once again, if a secondary diode is added, it will decrease the voltage passing to the 5101, if D17 is still good.

An alternate solution to a battery pack is to use a single CR2032 battery mounted on the MPU board in a holder. Lithium button batteries do leak, although it is not nearly as common or severe as alkaline batteres. If using a lithium battery, it should still be changed annually for piece of mind. Although it is a 3v battery, it does work well. The holder and the replacement batteries are low cost. See this Robotron-2084 link by Dave Langley for details. His method can be adapted to work with any of this era of MPU boards.

Battery Damaged Williams Driver Board



It is important to remotely relocate the batteries from the MPU board, unless using a lithium replacement. The potential is there for not only the MPU to become damaged, but other associated boards in the backbox. The pic to the left is a prime example of extended damage. The damage occurred in this instance, because the shuffle bowler this board came from was stored with the batteries still on the MPU board for an extended period of time (roughly 5-8 years). It's a costly shame, because this was an otherwise decent, clean, working driver board. The amount of repairs which have to be performed now are going to be extensive.

4.3 Wiring Connector Issues

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

4.4 System 6 MPU Board Issues

4.4.1 System 6 MPU Board Diagrams

Here are PDFs of the MPU Board for System 6 games. These documents contain information that should be helpful when fault finding or identifying components and their locations

System 6 MPU Assembly Drawing

Because IC9 and IC10 can be bypassed directly, these diagrams are accurate for System 6a.

System 6 MPU Logic Diagram

The Schematic is a logical rather than physical layout of the MPU Board. Meaning that while it shows the circuit connections correctly, it does not match the actual layout of traces on the board.

4.5 System 7 MPU Board Issues

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

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

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

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

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

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

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

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

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

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


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

8 - MPU board may be good. Is it looking for the Driver Board? (Like the missing 7th flash on a Bally MPU).

Make sure the Driver Board is connected and the "40-way" interconnect has continuity on all pins. From System 8 on there is no interconnect... so by System 9 MPU and Driverboard (and Sound!) are all one PCB.

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

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

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

Remember to do the "switch on, off and back on again quick" trick to see if you can get attract mode when reinstalling in a game after taking an MPU out. That's a classic Fonzarelli move, a "golden oldie" of the pinball world. Because lots of times that does the trick. Also if removing the Driver Board and reinserting it on the MPU board 'fixes' your problems and the boards will then boot correctly, then it points to the "40-way" connector needing to be replaced. Both header pins on the MPU and sockets on the Driver Board.

Parts: The 7-Segment display can be replaced with a KINGBRIGHT SA03-12HDB LED 0.3" RED DISPLAY. 5101 CMOS RAM. 5101-1 The low power version is needed, as it needs battery backup to hold RAM contents when the game is powered off. A 6821 PIA is a standard part. MC6821 MC68B21 are common. The 6820 designation is much earlier but also works. Other designations:

xx6821, xx68A21, xx68B21, where xx can be MC (Motorola) or HD (Hitachi Data) will all work. The 'A' in 68A21 means the PIA will run at up to a 1.5Mhz Clock , the 'B' in 68B21 means up to a 2Mhz clock, without any letter is up to 1MHz. Any final letter is Package type (P,S or L) P=Plastic S=Cerdip and L=Ceramic. Any of the above speeds or package types will work for this era of pinball, so you can ignore the letters and use any 6820 or 6821.

4.6 Connectors, connectors, connectors

Cracked solder joints on the header pins of a Williams driver board


With this era of game, most of them 30+ years old now, you will have problems with connectors. One of the most common issues is cracked solder joints on header pin connections to the PCBs. Some cracks are more obvious than others, while some can only be seen clearly under proper magnification.

Solder removed from the header pins of a Williams driver board


Although it can be somewhat time consuming and a tedious chore, it is best to remove the old solder from a header pin joint, and then add new, fresh solder. Performing this procedure is a necessity on these games to ensure reliability. The other option is removing the header pin connection completely, and replace with a new one.

If your game starts to reset for no reason during play, or when you flip both flippers, it may be worth first re-pinning the connectors at 1J2 on the MPU Board and at the outputs from the PSU. This is always a good step even if it does no

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