The game resets at random.

Random resets from the power supply DB1 bridge

Cause: The DB1 bridge on the power supply board, which feeds the +5 V and +12 V, fatigues; its solder joints crack, sometimes with black arc rings around the leads.

Checks

• Inspect DB1's solder joints for cracks or black rings.

Fix

• Replace DB1 with a 35 A bridge rated 200 V or more, with lug terminals.

Systems

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

Related tips

• Getaway: fitting a replacement beacon
• Resets from power supply connectors CN1 and CN2
• Resets when both flippers are held or in multiball
• Power supply board versions are not interchangeable
• Power supply board fuses (late games)
• Z1 on the power supply is a varistor, not a diac
• Power supply board versions and their +5 V filter capacitors
• Power supply CN1 pinout, pins 1-6

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