Check that battery power reaches the RAM at 5D

Steps

• With the game off, measure from ground to the last pin of the CMOS RAM at 5D.
• On revision 1 CPU boards the RAM has 24 pins, so check pin 24; later revisions use a 28-pin RAM, so check pin 28.
• You should see about 4.2 V; this is what keeps the settings alive.

Systems

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

Related tips

• Repairing battery corrosion on the CPU board
• Repair battery corrosion on the CPU board
• Replacement battery holder for the CPU board
• Fit a remote battery holder
• Battery orientation on Data East and Sega CPU boards
• "Memory Error, Open Door" or "open the coin door" at power-on
• Change the CPU backup batteries yearly, with the game on
• Battery voltage at the RAM but memory still lost

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