The game is dead or acts strangely and +5 V is missing or low.

No or low +5 V from the power supply

Cause: Most often bad .156 inch connectors on the power supply board. Next, the backbox bridge that supplies about +12 V DC to the regulator (open gives low +5 V, shorted blows the fuse), then the 2N6057 pass transistor, rarely the MC1723CP regulator, and leaking filter capacitors.

Checks

• Inspect and repair the power supply connectors.
• Measure the DC from the backbox bridge into the supply; expect about +12 V.
• If that is good, check the 2N6057.
• Look for leaking electrolytic capacitors and corroded traces under them.

Fix

• Repair connectors, then replace the bridge, the transistor (use a 2N6059) or the capacitors as found.

Unplug the game before working on the transformer, line wiring or power supply board.

Systems

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

Related tips

• No +5 V on a System 7 power supply
• Choosing replacement bridge rectifiers
• Power supply gives no +5 V
• Sound aux supply keeps blowing its 2N6059: shorted capacitor on the 30 V rail
• Resets continue after diode repair: power and connector checks
• Power supply board versions are not interchangeable
• 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 One, Clay Harrell (pinrepair.com)