Adjustments such as free play are forgotten every time the game is turned off; new batteries make no difference.

Settings are lost at power-off even with fresh batteries: bad battery diode D2

Cause: The battery isolation diode D2 on the CPU board had failed, so the batteries could not keep the memory alive.

Checks

• Measure the memory backup voltage with the game off.
• Test the diodes in the battery circuit on the CPU board.

Fix

• Replace D2 with the small-signal diode the manual specifies (1N4148; a 1N914 is equivalent), fitted the right way round.

Systems

• WPC-95

Games

• Attack from Mars

Related tips

• Battery power not reaching the RAM: diode D2
• Settings lost although the batteries are good (blocking diode D2)
• New CPU batteries go flat quickly
• Check the battery blocking diode D17
• MPU boots only some of the time
• Battery or memory cap won't hold settings
• Test a playfield switch diode
• Spare diodes for coils and switches

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