Switches behave strangely: several closures for one switch, wrong switch numbers, or none at all.

Erratic switches after a ball hit a top-side switch

Cause: A switch diode above the playfield has been bent by a ball and is touching the switch leads.

Checks

• Look over every switch on top of the playfield before going under it.

Fix

• Straighten or replace the diode and make sure it clears the switch blades.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Use a real ball in the switch test
• How Data East switch numbers map to rows and columns
• False switch readings only when several switches are closed

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three, Clay Harrell (pinrepair.com)