At switch-on the game asks for the coin door to be opened ("Memory Error, Open Door" on The Simpsons and earlier, a shorter "open the coin door" prompt on dot matrix games). After opening it the game boots but has lost its audits and settings, and asks again next time.

"Memory Error, Open Door" or "open the coin door" at power-on

Cause: The RAM contents were lost because the three AA backup batteries on the CPU board are flat. Opening the door releases the memory protect switch so the game can reload factory settings.

Checks

• Measure the batteries.
• Check the battery holder for corrosion.

Fix

• Replace the batteries; if the message continues, check diode D25 and the RAM supply.

Systems

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

Related tips

• New batteries but still a memory error: check D25
• Check that battery power reaches the RAM at 5D
• Repairing battery corrosion on the CPU board
• Repair battery corrosion on the CPU board
• Replacement battery holder for the CPU board
• Battery orientation on Data East and Sega CPU boards
• Fit a remote battery holder
• Coin door test buttons bypass the switch matrix

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