The credit display is mirrored on the player 1 display and the game will rarely start a game; displays work in test, and a factory reset helps only until the next power cycle.

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

Cause: Hacked wiring on the coin door was letting switch wires short to ground. The switch lines share PIA ports with the display data, so a grounded switch upsets the displays (and sometimes lamps).

Checks

• Unplug the switch connectors on the right side of the MPU and see if the display fault clears.
• Inspect the coin door wiring and start button for wires or lugs touching the door or each other.
• Swapping MPUs also shows whether the fault follows the board.

Fix

• Repair the coin door wiring so nothing shorts to ground.

Systems

• Stern MPU-200

Games

• Meteor

Related tips

• Three displays dead and no high score shown: solder blob on a display connector
• Will not start and ignores coin door switches: check J3 wiring and door ground

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