A pop bumper coil locked on and burned (smoke under the glass, blown fuse F8 and a dead driver transistor). After a new coil, transistor and fuse, the fuse blows again a few seconds into a game and the new coil now reads 0 ohms.
New pop bumper coil burns up too: replace the driver's diode and resistor as well
Cause: When the first coil locked on, other parts in that driver circuit on the board (its diode and possibly a resistor) were damaged as well. With them faulty, the pop bumper fires once and then locks on again, destroying the new coil and transistor.
Checks
- Before powering up after any locked-on coil, test the coil's resistance, the driver transistor, and the diode and resistor that go with it on the driver board.
- Compare readings with the neighbouring driver circuits.
Fix
- Replace the driver transistor (Q10 here), the associated diode and, if damaged, the resistor on the board.
- Fit a new coil and the correct 3 A slow-blow fuse, then test in solenoid test before playing.
Games
Source: Pinball Repair help group!! (Facebook group)