Partway through a game a credit dot shows up. While it is lit, the bookcase turns back and forth instead of holding position in multiball and the swamp lock stops counting balls correctly. The bookcase optos look fine in switch test.

Credit dot appears and bookcase cycles during multiball

Cause: An intermittent connection in the bookcase opto wiring connector, so the bookcase position optos drop out for moments at a time.

Checks

• Enter switch test and watch the bookcase opto switches.
• With the test running, gently wiggle the connector that feeds the bookcase optos. If the opto readings flicker on and off, the connector is the fault.
• If the connector is solid, check the opto supply voltage while the bookcase is running and wiggle-test the harness with a meter.

Fix

• Power off and repin the bookcase opto connector with new crimp pins (and a new housing if it is worn).
• Re-test in switch test while moving the wiring to confirm the readings stay steady.

Systems

• WPC Fliptronics

Games

• The Addams Family

Related tips

• Ball keeps bouncing out of the Thing scoop: guide rail steering it to the side

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