A pop works only some of the time, fires by itself or fires several times, sometimes when other coils fire.
Pop bumper fires erratically or several times
Cause: C4, the filter capacitor for the board's two TTL chips, has gone open from the coil's current spikes. Because it fails open rather than short, it is often overlooked.
Fix
- Replace C4 with 47 mfd or, better, 100 to 200 mfd at 10 V or more.
Systems
Related tips
- How the pop bumper driver board fires its coil
- A pop bumper never fires
- Pop bumpers fire on their own or work only sometimes
- A pop bumper doesn't work at all
- Add power and fire LEDs to a pop bumper driver board
- Under-playfield pop bumper driver boards protect the coils
- Pop bumper locks on as soon as a game starts
- How the System 80 pop bumper driver board works
Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part One, Clay Harrell (pinrepair.com)