A motor won't stop, or a game feature doesn't reset to the right position.

Motor coasts past its stop: broken armature spring

Cause: On motors with a spring-loaded armature (Williams and most makers other than Gottlieb, which uses a brake blade on the score motor frame) a broken spring leaves the gears engaged after power-off, so the motor coasts past its intended stop.

Checks

• Remove the motor and check the armature spring pushes the armature gear clear when unpowered.
• Power the motor on the bench from a 30 or 50 V AC transformer and watch it engage and release.

Fix

• Replace the spring. Too strong and the gears never fully engage (and strip the first gearbox gear); too weak and they won't release. Expect some trial and error.

Systems

• Electro-mechanical

Related tips

• Vari-target doesn't fully reset and the score motor keeps running
• Score reels reset slowly: sluggish score motor or game motor
• What to match when replacing an EM motor
• Converting a 50 V motor for 24 V use

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