On the bench, F3 on the power supply board blows at power-up. It still blows after lifting the parts in the suspect high-voltage section, which should leave it no path to ground.
Power supply fuse blows with the circuit isolated: carbonised burn on the board
Cause: An earlier failure had burned the board at a via. The charred board material was conducting into the 12 V trace running beside it.
Checks
- Look for darkened or burnt fibreglass around vias and traces, even if the damage looks small.
- Check the burnt area for resistance to neighbouring traces, not only to ground.
Fix
- Cut or drill out all the carbonised material, then repair the trace with wire.
This supply makes the high voltage for the displays; let it discharge and work on it unplugged.
Games
Related tips
- Flippers die after being held a few seconds, then recover
- Solid state flipper has no power though fuses are good
Source: Pinball Repair help group!! (Facebook group)