A game starts normally, but after 30 seconds to a minute of play, once a few coils have fired, it goes back to attract mode. Some coils seem to set off others (flipping or a pop bumper hit resets the drop targets). Swapping in different MPU and solenoid driver boards changed nothing.

Game drops back to attract mode a minute into play: ball trough switch stuck closed

Cause: The ball trough switch was stuck closed all the time.

Checks

• In switch test, watch the outhole and ball trough switches with no ball on them.
• Check switches close to coil mechanisms for blades touching coil brackets or lugs.

Fix

• Re-gap the trough switch so it opens fully when no ball is on it.

Systems

• Bally MPU AS-2518-35

Games

• Paragon

Related tips

• Coils fire in test but trough and popups don't work in a game: trough switches
• Multiball balls not released, game loses track of balls: trough switch actuators
• Boots with 7 flashes but won't start a game or play its tune: outhole ball switch
• Multiball game will not start: ball or trough switch out of place
• Gold ball and play ball both end up in the normal trough: gold ball switch wire bent
• MPU won't boot and driver board test points read low: replace the solenoid driver board

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