Hitting a lit mushroom switch pulls in the series relay in the cabinet, and it stays in, so the 10-point score reel keeps advancing. Everything else, including the 10-point reel in normal play, works.
10-point reel keeps scoring after a mushroom hit: series relay coil stuck on
Cause: The series relay's coil was faulty (badly discoloured) and the relay stayed pulled in even with no power on the coil. Its one switch feeds the 10-point relay, so it must only close briefly.
Checks
- Watch the series relay when a mushroom switch is hit: it should drop out again at once.
- Rule out stuck 10-point playfield switches and a dirty or broken end-of-stroke switch on the reel.
- Look for a discoloured or overheated relay coil.
Fix
- Replace the series relay coil (or the relay), then retest the mushroom switches.
Unplug the game before working on relays: parts of an EM's wiring carry line voltage.
Systems
Games
Related tips
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Source: Pinball Repair help group!! (Facebook group)