The solenoid test fires coils in a jumbled sequence.
Solenoids fire out of order in solenoid test
Cause: A bad PIA on the MPU board.
Checks
- Swap U10 and U11; if the fault changes, one of them is bad.
Fix
- Replace the bad PIA.
Systems
Related tips
- Wrong coil fires or a coil never fires
- How Bally coils are switched
- Solenoid selection: four MPU lines decoded by a 74154
- Flippers and some coils work, others are dead
- Solenoid select lines: MPU PIA U11 to SDB 74154 pin map
- Use the solenoid test to find a coil that does not fire
- No coils work at all
- How the MPU sees the 43 V solenoid supply
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)