The upper playfield pop bumpers fire but give no score or sound, and continuity from the pop score switches back to the MPU checks out.
Pop bumpers fire but don't score: bad switch diode on the diode board
Cause: The diode for the pop bumper scoring switches, on the diode board under the playfield, had failed.
Checks
- Find the pop bumper switch diode on the schematic and on the diode board, and test it with one leg lifted.
- Check that the score switch stack on the pop is not squeezed closed.
- The switch input chip (a 7404) can be checked by swapping it with its socketed twin.
Fix
- Replace the diode; a member recommended the original germanium 1N270, or a 1N914 or 1N4148 if that is not available.
Systems
Games
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Source: Pinball Repair help group!! (Facebook group)