Switch 37 shows closed in switch test, and keeps doing so with the switch connectors (J2 and J3) unplugged, so the fault is on the board.

Switch reads closed even with switch connectors unplugged: shorted resistor on the MPU

Cause: A 56k resistor (R42) in that switch input line on the MPU had shorted.

Checks

• Unplug the switch connectors to prove the fault is on the board.
• With a logic probe, the switch return inputs should sit steady high with nothing connected; one that pulses points to its input parts.
• Check the resistor and capacitor between the edge connector and the PIA for that return line.

Fix

• Replace the shorted 56k resistor.

Systems

• Stern MPU-200

Games

• Meteor

Related tips

• One drop target only registers if it is the first one down: reseat and clean the PIAs
• MPU switch connector pins J2 and J3
• Bally switch matrix: 5 strobes by 8 returns, numbered 1 to 40
• Odd switch problems from corrosion at the DIP switches
• Player 1 display shows credits and ball in play
• Switch 3 shows closed and scoring goes haywire: check the coin switches
• A display not working from MPU or sound board faults
• Fourth drop target won't count when lit, but works in switch test: MPU fault

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