Williams Pinball CPU/Computer Board Repair - Page 2

Note: I have several repaired System 9 and 11 boards for sale, and  I also repair these boards.  Please contact me for details. 

Page 1 of this board repair and CPU tester page

6802/6808 Adapter for HP Logic Analyzers
In August 2009, I made an adapter to easily connect my logic analyzer to the address, data, and control lines of the CPU chip.  It allows complete access to the operation of the CPU board core.  This board is a modification of the 68B09 adapter from the WPC project.

Adapter board in operation on a System 11 board.  This allows me to
accurately trace the program execution and better find what is wrong
with a board.

CPU chip trace
Typical view of Logic Analyzer connected to a CPU chip.  The last two lines
are spare signals that the user can clip to the board (blue clip in image above).

Logic Analyzer Adapter for 16 pin DIPs
I had some small amount of space leftover on the above circuit board for the Logic Analyzer, so I added two smaller boards.  One is shown here, and allows a LA pad to monitor all 16 lines of a 16-pin DIP IC.

This adapter allows a straight-through connection of a 16 pin DIP and provides a
tap for a LA pod.  All 16 pins of the DIP can be easily accessed.

LA screen display with an example test.

Siamese board setup with the Logic Analyzer
What is better than a CPU board being observed by a Logic Analyzer?  Why two boards of course.  After 10 years of repairing boards, I have encountered one or two that pass all tests on the individual components, but still do not boot and run.  I needed a brute force way of finding the problem, and imagined a setup where a good reference board was compared step-by-step with the bad board.  The setup below shows this configuration.

Siamese CPU boards
Twin boards on the Logic Analyzer to find why one does not work.

The crystal oscillator and reset circuit from the master board is used on the slave board by removing selected components from the power up reset circuit and the crystal oscillator.  They are passed by a three wire bridge shown as the grey cable in the image above.  This grey cable plugs into the sound CPU socket.

With this setup the two boards will run precisely in sync and their data and address busses will have identical contents (using identical copies of the game ROM of course) until the bad board deviates.  By inspecting the data and address busses, we can see why the bad board has failed.

Logic Analyzer screen setup
Screen snap of the Logic Analyzer for the Siamese setup

The above screen shows an example output of the siamese setup.  The first box shows a write to ram location 0x9B and 0x9C with the number 0x2100 (big endian).  The second box shows a read from that same location, and we see the same data coming out of RAM.  However, on a second read a few clock cycles later, this data is now 0x9B82.  After replacing the RAM chip and seeing no difference, I realized that the problem was with the RAM power circuit.  Indeed repairing that issue fixes the bad board.  Success.

Other uses of the Logic Analyzer with a CPU board
Logic Analyzer to investigate sound board commands
The Logic Analyzer can also be directed plugged into
the CPU board to investigate the commands sent to the sound board.
The board at the bottom of this image is explained below.

  Click here for the next page: Williams CPU Diagnostic Test Module

Testing Sound Boards
System 11 sound board test
Interconnection with sound board (click for big image).

The above diagram shows how the System 11 Sound board connects to the test setup. Both the D-11581 and the D-11298 sound boards interconnect with the same harness set.  

Tee for sound board
Power 'Tee' for the sound board

I made a special 'Tee' cable to provide a power tap for the sound board.  It is shown in the photo above, partially demated to show the construction.  The top colored ribbon goes to my CPU tester, while the grey is to the sound board.  The black plastic is a double male (board type) connector that allows the top connector to plug into the top of the middle one.

1J21 command board
1J21 command simulator with a Jokerz sound board.

The 1J21 connector on the CPU board sends sound/music commands to the external sound board, and I built a small command generator (shown above) to be able to test without a CPU board.  All that is needed is the conventional 5/12/-12V supply.  With the logic analyzer, I can see the byte sequence to send, and the board can be completely tested with this small fixture.  Video is in the image below.

One issue with testing sound boards is that quite often they require multiple AC voltage sources that are stacked to form Center Tapped outputs.  For example, the pre-DCS WPC audio board needs 24Vac that is Center Tapped.  Using the discarded transformer from a large UPS, I was able to put together a supply that offers great flexibility.

Multi-output transformer from an old UPS.  My trusty variable
transformer (blue box) is in the background.

I know that one winding of this transformer was designed for 120Vac, so we can use that as the primary.  It was now a question of what other winding ratios this transformer had and if any are in the useful range.  

An important tool for this kind of investigation is a variable tranformer like the one you see in the image above (blue box).  It allows you to gradually raise the line voltage for tests like these.

I first started by measuring the inductance of all the windings and using a DVM to see which windings were isolated.  The primary needs to have an inductance of at least several hundred mH.  This will keep the quiescent magnetizing current down to reasonable levels.  Once that is determined, I applied the output of the variable transformer to this winding with a current meter in series.  I could see less than 10mA of current flowed once I cranked the voltage up to the full 120V (make sure all output wires are not touching).  Now that the transformer could be safely powered from line voltage, it is a simple matter of measuring the output voltage and phasing on all the other windings.  I then mounted a barrier strip to the transformer and wired everything to it for easy access.  The 120V leads are terminated with the white pair visible above, which lead to a 120V power plug.  Incidentally, this power plug is from a discarded Christmas lighting set which has two integrated tiny fuses.  I then stacked the resulting five windings to get me a variety of outputs depending on which taps I used.  I know can have 20VCT (20Vac total, Center Tapped), 16VCT, 56VCT, and many other assymetric combinations.  This will come in very handy in future audio board tests.

System 11 Display Data Tester
The System 11 displays have two rows.  The top row is alphanumeric, thus it is able to display numbers as well as the complete alphabet.  The bottom row is numeric only for  11A and B, but alphanumeric for 11C.  Each row is 16 digits wide, so a total of 2x16 of display data.  My desire for this tester is to display a particular row and column to isolate what is happening with the control lines.  This examination and use is not convenient to do with the high-voltage displays, and I thought it would be too expensive to buy both types of LED displays as diagnostic tools (about $300 each).  I decided to make a single digit alphanumeric display.  I could then use it to display the information in a particular row and column of the larger display.

Display Data Tester
The display data tester connected to a System 11A board.  
"HIGHEST SCORES" is being output by the board
and the first two columns are displayed.
The columns are selected by the blue/green jumpers.

I started the project by looking for an inexpensive single digit alphanumeric LED display, but found that it was cheaper to buy them as twin digits.  In looking at the schematics, it was also clear that the easiest thing to do would be to show both the top and bottom digits of the selected row(s).  The user is able to select which two columns of the 16 to display.

The image above shows the completed tester.  It connects to 1J22 and 1J3 for the segment information, and the two columns selected for display is controlled by connecting the blue and green jumpers (connecting to 1J1 for the left 8 digits and 1J2 for the right 8).  It can work for any System 11 board but it requires the changing out of four of the chips to go from 11AB to 11C.  This is due to the data difference between the generations of boards.  System 11C board have all their segment data inverted from the previous generations.

The video below shows the display scrolling "HIGHEST SCORES".

Display Data Tester isolates the data from two of the 16 columns of the display.
The flashing is because this video is being played in slow motion.

Testing Power Supply Boards

I also built a test setup for the System 9/11 power supply boards.  They include an AC multi-output transformer (left) for feeding the low voltage sections, and a connection to my variable transformer for the high voltage circuits.  This latter arrangement allows me to turn the input voltage up gradually to prevent damage in case of a fault, and allows me to check how well the board regulates the output high voltage.  These plug into the unusual 3x4 pin 3J1 connector.

2532/2732 Adapters
Some early System 3-7 CPU boards use 2532 ROMs.  These are similar to 2732s except for a slightly different pinout, and were originally made by TI.  My PROM programmer, the Dataman S4, does not have an entry for the 2532, so I decided to make adapters to program these ROMs.  I used a wire-wrap socket and a conventional socket stacked on top of each other.  This is shown on the left in the image below.  I found that using the Toshiba setting for the 2732 worked best on my Dataman.

ROM adapter
Adapters to allow a 2532 to be plugged into a location for a 2732 (left)
and using a 2732 into a location meant for the 2532 (right).

Since I was making the adapter anyway, I decided to make the reverse adapter.  Namely one that allows the use of a 2732 ROM in an application requiring a 2532.  That is shown on the right above.

A note on System 9 to 11 conversions (sound)
In July 2016, Joe George sent me his findings on using a System 11 in a Space Shuttle

Since my System 9 CPU Board quit working, I converted a base System 11 board to work in System 9 following the instructions at the end of the System 9 Troubleshooting Guide I found at http://gamearchive.askey.org/Pinball/Manufacturers/Williams/pdfs/pinball_troubleshooting_sys9.pdf. It turns out though the memory map in the manual is wrong. It implies that the 4 2732 speech ROMs would be stacked in order (U4, U5, U6, U7) into a 27128 ROM for the System 11 Sound ROM at U22. However, the memory map is wrong, and for some reason the Space Shuttle manual I have doesn’t include a schematic for the speech board, so I couldn’t tell that the conversion doc was wrong.

I found a Speech board schematic in the manual for Sorcerer and it said the memory address space was occupied by (in order) U7, U5, U6, U4. I stacked the 4K speech ROM images I had from the speech board in that order and reburned a 27128 ROM, and my speech works great now!

Other CPU Testers
These are Ebay auction prices and photos I have gathered over the years on these testers.  The Williams factory appeared to have made three kinds of board testers.  One for System 3-7, the second for System 11 (and 9?), and two WPC testers (WPC89 and WPC95).

February 2006, this System 3-7 tester (6253871562) was $665+$70. 

Close-up of the control panel of the above tester.

Feb 2006, this System 11 tester (6254290420) was $366+70.
It looks home-made.

Close-up of the test panel.  Note lack of solenoid and lamp matrix displays.

Feb 2006, this System 3-7 unit (6255704954) was $474+shipping.

Closeups of the test panel.

Video of System 3-7 tester in operation.

February 2007,  this WPC95 tester (110093911411) was $1500.

The I/O panel looks like it includes a matrix of lamps (similar to my tester),
and a matrix of switches.  One can also see test lamps for solenoids and other

Close-ups of the above WPC95 tester.https://accounts.myuhc.com

September 2007, this System 3-7 tester sold for an amazing $1200

In March 2008, this System 3-7 tester sold for $515 (160213461303). 
It is highly incomplete.

April 2008, this System 3-7 tester was $688 (130209246482).

June 2008, this System 3-7 tester was $236 (320258934586)
It was missing its boards and the upright panel.

Sept '08, this System 11 tester sold for an amazing $1435 (
I am always amazed how much these units sell for compared to my tester.

Nov 2008, this System 11 tester (110312219131) was $550.

July 2009, this System 3-7 tester (140329614857) was $500+$50.

Oct 2009, this System 3-7 tester (250506825123) w/o driver board
was $160 (IL pickup only).

Oct 2009, this WPC89 tester (250506810477) was $635 (IL pickup only).

In Dec 2009, this new WPC89 tester (320457377514) was an amazing $3900.

In March 2010, this WPC-95 tester was $2600 (280476266131).

April 2010: This System 3-7 was $560 (Ebay: 260579868990).

<iframe width="560" height="315" src="https://www.youtube.com/embed/rm-txtn1kAM" frameborder="0" allowfullscreen></iframe>Ebay #112108025438
August 2016: This 3-7 tester was $1400 (Ebay: 112108025438)



  • October 26, 2005 - Purchased first nonworking CPU board for $40 + $10.  Previously, I had seen untested units on ebay in the range of $31 (burn damage) to $175 (clean).
  • November 7, 2005 -  Initial checkout complete.  Board is mainly working.  Only K1 still missing (on order).
  • November 10, 2005 - Completed initial breadboard concepts for CPU tester.
  • November 25, 2005 - Initial layout of circuit board complete.
  • November 26, 2005 - Purchased a second nonworking CPU board for $23+$14 on ebay.  When powered up, it passes CPU self-test, and lamp matrix works fine.  Further testing in the future.
  • December 01, 2005 - Arrival of the finished CPU tester boards.
  • December 03, 2005 - Initial testing of the CPU tester complete.  Lamp matrix, switch matrix and LCD interface operational.
  • December 11, 2005 - Software development of the Microprocessor in progress.
  • December 26, 2005 - Software development mostly complete.  Kit is made available.
  • January 13, 2006 - Initial orders and parts are in.  Manual is half written.  Assembly of first round of units begins.
  • January 21, 2006 - Initial orders complete and ready to ship.
  • February 1, 2006 - First use of tester to repair a CPU board.
  • February 19, 2006 - A nice endorsement from Peter regarding the CPU tester.
  • February 20, 2006 - Auctions for two CPU testers on ebay.
  • March 14, 2006 - Due to popular demand, I built a second batch of testers.
  • March 24, 2005 - System 11 compatibility added.
  • August 7, 2006 - First unit sells with BIN on ebay for $500 (item #170016357842).
  • July 2, 2007 - Case #6 documented.  Conversion to MOSFETs for the high-side lamp matrix driver.  This board was bought on Ebay for $35 (+$15).
  • August 2009 - As of this date, I have successfully repaired more than 50 System 9 and 11 boards.  I am glad to say that despite the varied challenges (battery leakage, burns, failed parts, etc), I have not failed to repair a single one.  That is about one board per month since 2005.
  • August 2009 - Made adapter board to easily connect Logic Analyzer to a 6802/6808 CPU chip.
  • May 2010 - Added System 3-7 mode to CPU tester.
  • October 2011 - Added power supply test fixture.
  • March 5 2016 - Added Siamese setup.
  • May 2 2016 - Added DIP16 breakout board.
  • Jan 22 2017 - System 8 board repaired with tester.
  • June 15 2017 - Display Data Tester.
  • January 26 2019 - Multi-output Transformer

Note: I have several repaired System 9 and 11 boards for sale, and 
I also repair these boards.  Please contact me for details.

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