Interestingly the sound boards for the Williams machines of this era, are basically stand-alone mini-computers that are just triggered with which sound to play, by the main CPU board.

Think of it kind of like a door-bell, where you can press different buttons to get different sounds as you go down the street.

So I was researching the best way to test the boards (I have no sound at the moment) and there is this amazing video of some nerdy guy who used to repair arcade machines in the arcades in the 1980’s, who used to take home all the sound boards from dead arcade machines (Williams’ Defender in the case) and turn them into door-bells himself.

Check this out – it’s quite amazing 🙂

“Back in the day when I was an amusement machine mechanic I used to salvage the old sound units from video games and make them into doorbells or whatever, this is a typical example of basic operation. What is curious about the technology used in this is complex layers of FM modulated waves to produce a really sci fi sound, generated by a 6800 series CPU and piped through an 8 bit A-D. Most video games of the time used a yamaha synth chip. This one is Nowadays of course I build my own sound effects units.”

So you can basically actually build a totally separate test circuit (power and speaker) for the Williams Sound Boards, and test them individually without needing the rest of the system connected. have a great tutorial on how to test the boards with a logic probe, and this guy in Belgium (pinball expert Leon Borre) has a superb break down of how to build your own harness to test these boards, and even include a special ‘test rom’ that lets you flash an LED on and off at certain points of the board to show power working and any issues

You’ll need the board reference PDF showing which version of the board you have and the correct Sound ROM installed and in case you wonder where you are going to get -12V for your test rig from, the Williams Guru, Dave Langley, says you can just use the standard -5V you get from your switching power supply to do this instead and it will work fine.

Off to build one of these over the weekend and see what we can generate 🙂


Williams sound card repair

Youtube video of Defender converted

Dicussion about how to repair

Detailed descriptions of how to fix

Two of my Williams sound boards, one jumpered for Defender, the other jumpered for Robotron / Joust

Williams Sound Boards

You can also use a 6802 mpu instead of the 6808 mpu and the 6810 external memory as described here