The sound board is its own computer
Each sound board has a 6802/6808 CPU, a 6810 RAM, a 6821 PIA and a 2716 or 2532 EPROM, plus its own reset circuit. At power-on CPU pin 40 (reset) is held low briefly then goes high; the 3.58 MHz crystal clock appears on pins 38 and 39. The board makes its own supplies: 12-18 V AC from the transformer at 10J1 goes through a small bridge and filter cap to unregulated +12 and -12 V, and a 7805 gives +5 V. There are one or two fuses for the incoming AC.
Systems
Related tips
- Sound board completely dead
- Sounds don't match the game or die mid-game: sagging 7805 on the sound board
- Which sound board each game uses
- Sound board jumpers for 2K sound-only games
- Using the sound board test switch
- Powering a sound board for testing
- How System 3-6 games trigger sounds
- Setting up a sound board for speech
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)