The background music cuts out now and then and comes back on the next ball, while sound effects keep working. Recapping and reflowing the sound board and power supply changed nothing.

Background music stops at random until the next ball: game ROM bug

Cause: A bug in the original game ROM: if the outhole kicker fires twice, the background sound is switched off.

Checks

• Watch the outhole kicker: does it sometimes need two kicks to clear the ball?

Fix

• Make the outhole kicker eject reliably on the first kick.
• Or fit the later bug-fix game ROM (the original poster burned an L3 EPROM).

Systems

• Williams System 6 / 6A

Games

• Time Warp

Related tips

• Sound EPROM files used by System 3-6 games
• Game locks up mid-game, sounds stop and displays go out: MPU connectors and loose ROMs
• Powering a sound board for testing
• Sound board supply facts
• Background sound never stops at game over: sound-line driver chip
• System 6/7 sound and speech board ROMs
• Sound board jumpers for sound-and-speech games (2K ROM)
• Intermittent sound: sockets and old ROMs

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