Each time the spinner moves, other switches in the same matrix row register (mostly a pop bumper), the GI flickers and the score displays garble. The switches all test fine at the MPU with a switch tester, and the fault stays even with the spinner switch disconnected.
Spinner hits garble the displays and trigger other switches: post screw touching GI
Cause: A wood screw for a GI lamp socket under the playfield met one of the spinner bracket's post screws inside the playfield, putting GI AC onto the spinner frame and, through the spinner and switch blade, into the switch matrix.
Checks
- Move the spinner by hand with the game on and watch for flicker or garbled displays even with its switch held open.
- Under the playfield, look around the spinner bracket post screws and T-nuts for GI wires, staples or socket screws that could touch them.
Fix
- Move the GI socket screw (or re-route the wire or staple) so nothing on the GI circuit touches the spinner mounting screws.
Systems
Games
Related tips
- Drop target and spinner on one switch row dead: wire hanging off the slam tilt switch
- Switch reads closed even with switch connectors unplugged: shorted resistor on the MPU
- Switch 3 shows closed and scoring goes haywire: check the coin switches
- One drop target only registers if it is the first one down: reseat and clean the PIAs
Source: Pinball Repair help group!! (Facebook group)