The line fuse has blown and the red disc next to the line filter is cracked or burnt.

Fried varistor at the line filter

Cause: The varistor across the line filter shorted to absorb a voltage spike; it protects only once.

Checks

• Inspect the red disc varistor at the front left of the cabinet near the auxiliary outlet.

Fix

• Replace the varistor. The game runs without it but has no surge protection.

Line voltage is present in the cabinet; unplug the game before working on it.

Systems

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

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