Williams sound board layout
Here’s a collection of sound board failures and fixes.
The most common failure I’ve seen on Williams Video Game System sound boards is the 6808 CPU itself. If you logic probe the address and data lines and any appear dead, suspect the CPU. I’ve gotten replacements from Twisty Wrist Arcade here: https://www.twistywristarcade.com/processors-40-pin-ics/1118-mc6802p.html. The 6802 is functionally identical to the 6808, it will drop in without any modifications. 6802s have their own internal memory which can be enabled with a trace cut on the sound board, thus eliminating the need for the 6810 RAM module. (Modification seen here: https://www.robotron-2084.co.uk/techwilliamshardwareidsound.html) This could be beneficial in instances where the 6810 RAM has failed.
I’ve only seen one failure of the 6810 RAM module, the sound playback worked, but the sounds seemed to be of an incorrect pitch. you may get sounds that just repeat over and over. you can kill two birds with one stone with the 6802 CPU mentioned previously, as that can replace both the 6808 CPU and the 6810 RAM module. (see modification above)
I’ve seen several sound boards with bad crystals too, even once where it worked intermittently (sound would function for awhile and then just quit). I’ve gotten replacements from Mouser in the past here: https://www.mouser.com/ProductDetail/815-AB-3.579545-B2
If the sound board plays sounds, but you notice that it’s playing sounds at the wrong times (like an extra life sound when it should be a fire sound), suspect failure of the 6821 PIA. This is a 40 pin chip directly next to the 6808 CPU, and is not socketed. It’s encouraged that for ease of replacement later that you remove the 6821 PIA and solder in a 40 pin socket.
If you run the Sound Test and some of the sound lines don’t play, this could be an issue with the green wiring harness between the ROM and Sound boards or the solder to the header pins could have cracked. Another very obscure failure of the sound playback calls from the ROM board to the sound board can be caused by bad IC5 4050 and/or IC6 4068. If you observe sound lines not working in the sound test this can be the problem. I’ve only seen this happen once, I was able to deduce it by following the schematics and changing the chips out.
The Sound boards have different strapping configurations for the Sound ROMs, for use with smaller 2716/2516 or larger 2532s. Defender and Stargate only use 2716/2516s while all Robotron and later games use 2532s. A mistake I’ve seen is use of Defender/Stargate sound boards with Robotron/Joust/Sinistar/Bubbles roms or vice versa. If the jumpers aren’t configured correctly, the Sound board will be unable to read the code in the ROM and will appear seemingly dead. Jumper settings can be found here: https://www.robotron-2084.co.uk/techwilliamshardwareidsound.html
One last obscure Sound board failure I’ve seen was on a Defender with one of the older Sound boards that was taken from Black Knight with a speech header. The customer said they didn’t do this, but rather whoever had the game before them; they tried reflowing the solder on the speech header Defender doesn’t use and bridged some of the solder pads. To date I’ve never seen one of the 20 or 40 pin headers ever develop cracked solder, so they should not be reflowed.