What the line filter does

The small metal box in the AC line filters radio-frequency noise picked up by house wiring that could upset the CPU board, and keeps the game's own noise off the mains.

Systems

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

Related tips

• Replace the +5/+12 V logic filter capacitor
• Judging the logic filter cap by AC ripple
• CPU LEDs stay on after recapping, only 8 V on the 12 V line: cap in the wrong hole
• Leave the big lamp filter capacitor unless it is leaking

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