The game misbehaves in odd ways, such as serving an extra ball after the last one before going to game over, or a ball count unit resting one position off when reset.

Game ends at the wrong time: stepper wipers off their rivets

Cause: The bakelite contact plate has shifted, so the wiper fingers sit off-centre on the rivets or even one rivet out.

Checks

• Reset the unit to zero and see where the wiper sits on its rivet.
• Step it a few times and check each position.

Fix

• Loosen the two to four screws holding the bakelite plate just enough to turn it, rotate it until the wipers centre, check every position, then tighten.

Systems

• Electro-mechanical

Games

• Sky Jump

Related tips

• Players, credits or ball count not resetting points to a stepper unit
• Ball count runs to 10 and the game resets endlessly: dirty ball count stepper
• Ball count stays at 1 after each drain: dirty secondary trough switch
• Ball count stepper won't advance: pawl arm frozen in old grease
• Double bonus not collecting: bonus stepper mainspring overwound
• Score motor runs on at game over: end game relay not pulling in
• Stepper cleaning, part 3: rivets, wipers and lube
• Wrong player comes up on ball 2 and scores won't reset: stuck P relay switch

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