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.


Testing Sound Boards

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.  


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.


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.




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.


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.


Testing plasma display boards

The above video shows a System 11A alphanumeric display board being checked out along with its associated power supply board.  The segment control lines for both display rows have been jumpered to +5 (all segments lit), and I select one column at a time by jumpering to one pin at a time on J3 and J4.  With my variable transformer I am able to apply the minimum of voltage to light the display digit.  Since I am not strobbing, I wanted to make sure I did not overstress the display by applying too much power.

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.



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".

• Schematic of Display Data Tester

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.

Part of the trickiest items to troubleshoot on this power supply board is the high voltage.  It is a linear regulator and fused by a tiny 1/4 Amp fuse.  Almost any kind of failure can easily cause you to burn through many fuses during a repair. 


Checking out the solenoid circuits for safe power up
Due to the high power circuits they contain, pinball machines can sometimes require great care when powering up an unknown machine or configuration.  One such situation is the solenoid power.  If a playfield switch is shorted closed (along with possibly an incorrect fuse), power could be enabled continuously to a number of solenoids.  The result can be melted coils, burned components, or even a fire.  I have repaired numerous boards that have complete holes burned into them.  I have always thought that it would be good to easily put in a way to checkout a newly acquired machine.  One way would be to replace the solenoid circuit fuse (F2) with another component that increases its resistance if current through it is increased.  After some thinking about it I realized that incandescent bulbs do this, and I decided to try this idea.

Some background, with the original 2.5 Amp F2 in place, I measured about 0.27 Amps of standby current on solenoid power.  Actuating a pop bumper caused 4.2 Amps of steady state current.  Since the fuse is slow-blow, this would have to persist a few seconds before blowing it.  I was able to keep the coil on for two seconds without blowing the fuse.  The unloaded solenoid bus measured 30.8V, and the pop bumper coil measured 3.8 ohms on my testbench.

My first try was to check to see what I had in storage and found that the #89 is the highest voltage bulb I have.  It is rated for 13V and draws 0.58 Amps at that voltage.  This is a resistance of 22.4 ohms at full brightness.  However, when cold I measured only 1.7 ohms.  That is an increase of better than 10x!  Since the solenoid voltage is about 30V on Space Shuttle, I decided to use two #89s in series and assembled the prototype with some alligator clips.  The results show that the current limiting effect was too strong and the pop bumper would not pull in.


For my second try, I purchased a #315 bulb.  It is rated for 28V, and 25W, allowing a current of almost one Amp.  Cold resistance is about 2 ohms.  That worked better as can be seen in this video.  When in use make sure that the bulb glows dimly with no solenoids activated (no shorts), and that the coil pulls in weakly when activated (no shorted coils or backwards diodes).  It is also a positive sign if you can manually move the coil and it stays latched.  This system should work for board sets that use 30V solenoid power such as System 7 and later. 


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.


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!

Pincoder's Test ROMs for System 3-7
In December 2019 I found this ROM set for testing various Williams systems.  One set focuses on the System 3-7 series and consist of a set of about two dozen ROM images.  The original intention was to burn a ROM for each test and put that into the IC17 spot on the board to run the test.  I immediately thought of building an adapter board with DIP switches to select the test.  Reading further I saw that indeed someone had designed a board for this purpose.  This design accomodated up to 16 types of tests, but the author of the ROM series had since increased the number of tests to about two dozen, requiring an upgrade to handle up to 32 tests.  

The board design by 'barakandl' made me wonder if a conventional perf board (with predefined traces) could work reall well and I decided to try and build a board.


Other Notes