What each 6821 PIA does
Through System 6 there are four PIAs in all: the CPU board PIA drives the score displays, and the driver board has one each for coils, lamps and switches. System 7 puts a fifth on the CPU board to trigger sounds and light display commas. The processor treats each PIA as a memory address, so a dead PIA normally freezes the game, and a CPU board with no driver board attached cannot start.
Systems
Related tips
- Why the solenoid and switch PIAs fail most
- Coils 1-8: connector, transistors, PIA pin
- Test the driver board PIAs IC5, IC10 and IC11 with Leon's code
- Coils 9-15 and coin lockout: connector, transistors, PIA pin
- Slings and pop bumpers feel sluggish: backbox boards loose with missing mounting screws
- Solenoid fuse blows at power-on and solenoids fire: driver board logic chips
- Slings and pops all burned at once: CPU lock-up from the 40-pin interconnect
- System 6 and System 7 driver boards can be swapped for testing
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)