A playfield coil locks on.
Coils lock on from a bad playfield ground plug pin
Cause: Besides the backbox ground fault, each playfield ground runs separately through a Molex plug to the copper ground strip; one pin with resistance can lock a coil on.
Fix
- Do the mandatory ground modifications.
- Tie all the ground wires together on the playfield side of the plug so one failed pin no longer matters, and tape the join.
Systems
Related tips
- Playfield coil chart: resistance and use
- Test an under-playfield 2N5875/2N5879 coil transistor
- Under-playfield pop bumper driver boards protect the coils
- Pop bumper locks on as soon as a game starts
- Coil sleeves by mechanism
- Lower playfield pop bumpers lock on or blow their fuse: shorted driver transistors
- Check every coil's resistance before first power-up
- Which coil lug the power wire goes on
Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part One, Clay Harrell (pinrepair.com)