GI lights flicker or are out; the GI connector on the power supply board is burnt.

Burnt GI plugs on the power supply board

Cause: Hot Tip, Lucky Seven and all System 7 games run GI current through power supply plugs (such as 3J9 on System 7), which overheat.

Checks

• Inspect the GI connector on the power supply board.

Fix

• Replace the GI header and housing pins (see part two of the guide for the GI connector section).

Systems

• Williams System 3
• Williams System 7

Games

• Black Knight
• Lucky Seven

Related tips

• Burnt GI connectors on the power supply (System 7, Hot Tip, Lucky Seven)
• Swapping power supply boards between generations
• Early Black Knights use the System 6 power supply
• No lamp matrix voltage
• All matrix lamps out, everything else works
• The 300 V circuit on Hot Tip and Lucky Seven supplies
• No general illumination: trace the 6.3 V AC
• How the lamp matrix runs 6.3 V bulbs on 18 V

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