After a power outage during play the game kept resetting; once that stopped it would take a credit but not kick a ball out, though the trough kicker and trough switches tested fine.

After a power cut: resets, then won't serve a ball

Cause: Disturbed connections plus failed chips at U20 and U14, apparently from the power event.

Checks

• Reseat all board connectors first (that alone stopped the resets here).
• Check that all the driver board LEDs are lit and the kicker fires in solenoid test.

Fix

• Reseat every connector.
• Replace the chips at U20 and U14.
• Run the ball-empty routine in the test menu so the game relearns where the balls are.

Systems

• WPC Fliptronics

Games

• Twilight Zone

Related tips

• Resets: +5 V at the driver board test point is low
• Outhole, shooter diverter and gumball motor all dead: CPU board chip at U4
• Reboots at start-up and when flipping: flaky power connector to the CPU
• Gumball diverter, popper and two bumpers dead in test: faulty CPU ribbon
• What a WPC game reset is
• DMD dead though display and controller work in other games: CPU board fault
• Watching the supplies while the game resets
• WPC CPU board LEDs at power-on

Source: Pinball Repair help group!! (Facebook group)