Suspected bad CMOS RAM.

Using CPU diagnostics to test the 5101

Cause: Failed 5101 at IC19.

Checks

• Get the game booted (audits or attract are both fine), then with the coin door open press the bottom test button on the CPU board.
• System 3-6: if neither LED goes out, replace IC19. System 7: a reading of 8 or 9 on the 7-segment LED points to the 5101.

Fix

• Replace the 5101 at IC19.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• System 6 won't boot and fails the 5101 RAM test even after replacing it: bad 5101 stock
• System 7 diagnostic display stays lit on a working game
• Replacing the 6802 CPU with a 6808
• Identifying a System 3 to 7 CPU board
• What changed on the System 6A CPU board
• System 6 CPU board test points
• System 7 CPU board test points
• System 6 CPU board jumpers J1 to J6

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)