A motor, GI section or other device fed by an under-playfield relay board works intermittently or not at all.
A relay-board-controlled motor or GI string misbehaves
Cause: Cracked or cold solder joints on the relay board are very common.
Checks
- Inspect the board's joints, especially the relay and header pins.
Fix
- Reflow every solder joint on the relay board.
Systems
Related tips
- Under-playfield relay boards and the PPB board
- All L or all R bank coils/flashers dead: PPB relay K1
- Low coil voltage from pitted L/R relay contacts
Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)