Find out how the board died: failures cascade to the PIAs
A coil that locked on, or a blown display high-voltage fuse just before the game died, can take out more than the obvious part: damage often runs back to the driving 6821 PIA and leaves the CPU locked up. Note which fuses are blown and look for a dark ring on top of a PIA, a sign it overheated.
Systems
Related tips
- Testing the 6821 PIAs in circuit with a meter
- Checking PIA outputs with the test EPROM running
- Other quick PIA checks: swap or touch test
- Leon test EPROM does not run: check the 6808 and its pins
- Displays out, flippers and ball eject dead after display glitches
- Wrong coils fire and drop target dead: bad PIAs, shorted coil diode and Q14
- System 11 CPU board won't boot after cleaning: worn ROM socket contacts
- System 11 NVRAM upgrade not working: fit it at U25, not U23 (sound RAM)
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)