Every so often during play the flippers stop working; when the ball drains, bonus counts and the next ball plays normally, then it happens again.

Flippers go dead in the middle of a ball: a switch closing on vibration

Cause: A switch that tells the game the ball has ended (in the drain or trough area) was closing from playfield vibration, so the game disabled the flippers as if the ball had drained.

Checks

• Watch switch test while tapping the cabinet and playfield to find switches that flicker.
• Check the outhole and trough switches first, then other close-gapped switches such as top lanes.

Fix

• Re-gap any switch that closes on vibration.

Systems

• Gottlieb System 80B

Games

• Gold Wings

Related tips

• Scores and credits sometimes lost at power-off, batteries good: failing 5101 RAM
• Game starts but no switches score and the ball isn't served: corroded A1-J6

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