The knocker and the flashers sharing its circuit don't work in test; every other solenoid does. The driver transistor (Q39) was shorted, but replacing it didn't bring them back.
Knocker and a flasher group dead even after a new driver transistor: burnt trace
Cause: The board trace on the component side at that transistor had burnt through. It still read continuous on an ohmmeter but couldn't carry current.
Checks
- Check the shared flasher group: if only one lamp in a group is out, suspect the bulb, then the socket (one socket was bad here too).
- After changing a transistor, check the traces on both sides of the board around it, not just continuity.
Fix
- Replace the transistor again if needed and bridge the burnt trace (a leg of the new part or a short wire to the next point on the trace).
Systems
Games
Related tips
- Solenoid driver transistor positions on the CPU and PPB boards
- Quick test for shorted TIP122/TIP102 drivers
- Rocky pop-up in the backbox won't fire, even with a new coil: bad driver Q41
- How a coil or flasher is switched: PIA to TTL to pre-driver to driver
- Random coils fire instead of flashers with a new driver board: relay has the wrong coil
Source: Pinball Repair help group!! (Facebook group)