The game boots into attract mode but will not start; coin switches and the coin door test buttons are ignored, yet the board's own test works and bridging J3 pin 2 to J3 pin 14 starts a game that plays normally.

Will not start and ignores coin door switches: check J3 wiring and door ground

Cause: Two wires were in the wrong positions in the J3 connector and the coin door ground was broken, so the coin door switches never reached the switch matrix.

Checks

• Check every wire position in J3 against the manual's wiring diagram, not just continuity.
• Check the coin door ground and the harness where it flexes at the door hinge.
• Use a jumper (or a switch test plug) on the switch matrix connector to see which switches the CPU recognises.

Fix

• Move the misplaced wires to their correct positions in J3.
• Repair the broken coin door ground.

Systems

• Stern MPU-200

Games

• Galaxy

Related tips

• Credit display copied to player 1, game won't start: coin door wire shorting to ground

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