A CPU-controlled coil stays on even after its transistors and 7408 test good.
Coil still locked on with good transistors and gate
Cause: The solenoid PIA IC5, or the 7408 itself.
Checks
- Pull the solenoid fuse. In attract mode, logic-probe the IC5 outputs (pins 2-17): all should be low except the coin lockout output (pin 17, high unless the game is at maximum credits).
- On the 7408 the output should be low; the PIA input low and the blanking input high. If both inputs are right and the output is high, the 7408 is bad.
Fix
- Replace IC5 or the 7408 as found; socket the replacement.
Systems
Related tips
- Coil locks on and new transistors don't help: a failed 7408 on the driver board
- Coil has power and wiring is good but still dead or locked on
- A low resistance coil points to a bad driver transistor
- Coils 9-15 and coin lockout: connector, transistors, PIA pin
- Kicker coil locks on again after a new TIP122: dead 7408 gate on the driver board
- Slings and pops all burned at once: CPU lock-up from the 40-pin interconnect
- CPU locks up as soon as the driver board is connected
- How a coil is switched on
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)