Chips that commonly fail on System 3-7 boards
The 6821 PIA (6820, 68A21 and 68B21 also work) fails often: it sits at IC18 on the CPU board (plus IC36 on System 7) and at IC5 (coils), IC10 (lamps) and IC11 (switches) on the driver board. The IC19 5101 CMOS RAM (500 ns or faster) is another common failure. Also stock 7402, 7406 and 7408 TTL, 4049 (switch returns) and 4069 (master display) CMOS, 74LS367/74LS368 in place of 8T97/8T98, and the correct CPU: 6800 for System 3/4, 6802 or 6808 for System 6/7.
Systems
Related tips
- Obsolete chips on System 3 to 7 CPU boards
- CPU chip types: 6800 on System 3/4, 6802 or 6808 on System 6/7
- Chips a System 7 CPU board needs to run the Williams test ROM
- Identifying a System 3 to 7 CPU board
- What changed on the System 6A CPU board
- System 6 CPU board test points
- System 7 CPU board test points
- Remove an old chip socket
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)