One point value stops scoring, or the game won't move on to the next ball; a coil may be humming.

A chime, bell or score reel coil is stuck on

Cause: A playfield switch has stuck shut (or a relay that a playfield switch operates has), keeping the coil powered.

Checks

• Stuck-on coils are hard to spot: look at the chime or bell plungers for one held up, and watch the score reels.
• Trace back from that coil to the switch or relay feeding it.

Fix

• Clean and re-gap the stuck switch or relay contacts.

Systems

• Electro-mechanical

Related tips

• Score relay stuck on, reel does not score
• Hundreds reel keeps stepping after reset: a stuck playfield scoring switch
• 1,000-point reels reset but never score for any player: failed 1,000-point relay coil
• Score reels keep spinning at game reset: stuck scoring switches on the playfield
• Hundreds score reel won't advance though the bell rings: relay switch gap too wide
• 1000-point relay, ball index and chime lock on: dirty score motor switch
• EM score reel will not reset to zero
• Every hundred-point score also adds a thousand

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)