Z1 on the power supply is a varistor, not a diac

The low-power solenoid line enters the power supply from a backbox bridge at connector C1 pin 2, at about 32 V DC, and passes Z1. The schematic draws Z1 as a diac but it is a MOV that shorts above about 50 V. It rarely fails, and usually does so violently.

Systems

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

Related tips

• Power supply board versions are not interchangeable
• Power supply board versions and their +5 V filter capacitors
• Power supply CN1 pinout, pins 1-6
• Power supply CN1 pinout, pins 7-12
• Power supply gives no +5 V
• A 520-5047-02 supply can stand in for a 520-5047-01
• Won't boot, only some lamps on: bad capacitor joints on the power supply board
• Alphanumeric games need the 520-5000-00 supply

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