Pressing start sends the game into a reset cycle that never ends, even though every score reel snaps back to zero quickly when tested on its own.

Game keeps resetting after pressing start: a score reel zero switch stays closed

Cause: The reset sequence runs until every score reel and stepper reports it is home through its 'open at zero' switch. One reel's zero-position switch was stuck closed, so the game never saw reset as finished.

Checks

• With every reel showing zero, check that the zero-position switch on each score reel is open.
• Also check the zero switches on the bonus units and steppers (for example a value stepper) and clean their wipers and contacts.
• If it is not obvious by eye, follow the reset circuit on the schematic and check each open-at-zero switch in turn.

Fix

• Adjust the stuck switch so it opens at zero, and clean it.
• Reflow the solder joints on the score reel switches; cracked joints there are common on games of this maker and era.

EM games run some circuits on line voltage; unplug the game before reaching into the backbox or under the playfield.

Systems

• Electro-mechanical

Games

• Jackpot

Related tips

• Players 3 and 4 reset but players 1 and 2 never do at game start
• Score reels won't all reset and the stepper keeps running: one zero switch
• Score reels keep spinning at game reset: stuck scoring switches on the playfield
• 10,000 score reel resets but never scores in play: loose wiper fingers
• Reset relay stays locked on after scores reset: loose zero-switch arm on a score reel
• 1,000-point reels reset but never score for any player: failed 1,000-point relay coil
• Clean and adjust score reel nine and zero switches
• EM score reel will not reset to zero

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