Why the solenoid and switch PIAs fail most
A shorted solenoid driver transistor can take out the 7408 feeding it and then solenoid PIA IC5. Coil or lamp voltage shorted onto switch wiring under the playfield usually kills the 7406 or 4049 buffer and switch PIA IC11. The lamp PIA IC10 rarely fails. Fix the short before fitting new chips.
Systems
Related tips
- What each 6821 PIA does
- Special solenoid control paths
- Test a TIP120/TIP102 solenoid driver with a meter
- Replacing IC5 rarely fixes specials that fail only in test
- 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
- Solenoid fuse blows at power-on and solenoids fire: driver board logic chips
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)