The 12-pin square plug carrying transformer voltages into the power supply is burnt.
Burnt 3J1 square power input connector
Cause: 3J1 carries all the AC inputs and can overheat; the six-pin 3J2 ground plug rarely fails.
Checks
- Inspect 3J1 for burnt pins or housing.
Fix
- Replace with Molex 09-18-5121 (board wafer) and 03-09-1122 (wire housing) with .093" pins.
Systems
Related tips
- Burnt 12-pin power supply input plug stops the game booting
- Square power supply plug part numbers
- Game shows ROM versions and speaks, then nothing (burnt 3J1)
- Cracked header pin joints on the power supply
- Replace the 3J6 logic power connector
- GI in at the power supply but not out: check the GI relay
- Burnt GI connectors on the power supply (System 7, Hot Tip, Lucky Seven)
- What the power supply board takes in and puts out
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)