A pop bumper, slingshot or kickback fires over and over or stays on, then burns the coil or blows a fuse.

Pop bumper or slingshot machine-guns on pre-Back to the Future games

Cause: Before CPU version 3 the special coils fire directly from their own switch, so a stuck or closed switch locks the coil on. A second switch in the matrix only scores the hit.

Checks

• Check the pop bumper spoon switch or slingshot switch for contacts touching at rest.
• Make sure the coil is tight in its bracket and the pop bumper yoke is not broken.
• Check the coil resistance once it has cooled.

Fix

• Gap the switch so it opens at rest.
• Replace any burnt coil and its fuse.

Systems

• Data East CPU Version 1/2

Related tips

• A coil has power but never fires
• Special coil locks on only when a game starts or diagnostics begin (pre-Rev 3)
• Several bank-switched coils or flashers dead, or firing the wrong device
• Check every coil's resistance before first power-up
• Always check the coil diode when a driver transistor has failed
• Finding a coil's driver transistor without a manual
• Firing a coil by grounding its TIP122/TIP102 tab
• Use the manual's coil/flasher chart to find driver transistors

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part One, Clay Harrell (pinrepair.com)