On a Gottlieb EM the vari-target stops short of its reset position and the score motor runs continuously.

Vari-target doesn't fully reset and the score motor keeps running

Cause: The vari-target is a small stepper advanced by the ball and returned by a reset coil and spring. Dirt or too little spring tension stops it reaching reset; the game runs the motor until it does.

Checks

• Test the reset with the playfield down in its playing position; tipped up it needs more spring than in play.

Fix

• Clean the rivets with 600 grit paper and lubricate very lightly with a Teflon lube.
• Move the spring anchor among its three screw positions to the lightest tension that still resets reliably; too much makes the target hard for the ball to push.

Systems

• Electro-mechanical

Related tips

• Motor coasts past its stop: broken armature spring
• Score reels reset slowly: sluggish score motor or game motor
• Drop targets don't all reset fully: rebuild the reset and face the worn reset bar
• Large Gottlieb drop target bank won't reset: worn or sheared pivot rod
• Setting drop target reset coils to prevent metal fatigue

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