A coil does not fire and its driver transistor fails again soon after replacement.
Driver transistor keeps failing on the same coil
Cause: The coil diode has been fitted backwards. On coils with a playfield-mounted 2N5879, a reversed diode kills that transistor at once.
Checks
- Check the diode band is on the lug with the DC power wire.
Fix
- Turn the diode round, then replace the transistor.
Systems
Related tips
- How the pop bumper driver board fires its coil
- Kickout coil melts its sleeve: shorted transistor on the transistor board
- Replace a shorted coil before firing a repaired driver
- Lower playfield pop bumpers lock on or blow their fuse: shorted driver transistors
- Test an under-playfield 2N5875/2N5879 coil transistor
- Replacements for the 2N5875 under-playfield power transistors
- None of the CPU-controlled coils fire
- A pop bumper never fires
Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part Two, Clay Harrell (pinrepair.com)