The top left pop bumper never fires, not even in coil test, while the other two pops work. It fires when the coil is grounded or when the driver transistor's centre tab is grounded.
High Speed pop bumper dead in coil test, fires with tab grounded: bad driver chip
Cause: A failed driver chip upstream of that coil's transistors on the CPU board.
Checks
- Ground the coil's driver transistor tab briefly: if the coil fires, the coil and wiring are good.
- Test the driver and pre-driver transistors with the meter's diode test.
- If the transistors test good, trace back to the logic chip that drives them.
Fix
- Replace the faulty driver chip (done here by a board tech).
Systems
Games
Related tips
- Coil fires when tested but not in game play: TTL driver chip
- Right sling locks on at power-up and a pop is dead: bad 7402 at U45
- Solenoid 12 flashers dead: one of the two series bulbs is open
- Pops and slings fire in coil test but not from their switches: ground wire pulled out
- Firing a coil or flasher from its TIP122/102 driver tab
- Special solenoid fuse blows at power-up: a pop bumper switch held closed
- CPU and driver board transistors by position
- Testing driver transistors in diode mode (board out of game)
Source: Pinball Repair help group!! (Facebook group)