Displays come on but then go dim or flicker.

Score displays light then dim or flicker

Cause: Dried-out 100 mfd 150 V filter capacitors in the high-voltage section.

Checks

• Check the high-voltage outputs at J5 under load.

Fix

• Replace C7 and C11 (System 3-6) or C1 and C3 (System 7) with 100 mfd 150 V capacitors.

The display supply runs at about 100 volts DC; work with the game off and the capacitors discharged.

Systems

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

Related tips

• All score displays dead
• Score displays weak, dim or dead with fuses good
• Display high voltage out of range
• Score displays fade in a scrolling pattern
• Upgrade R2/R5 and check R1/R4 in the display supply
• Lower the display voltage to 91 V to extend display life
• Fit 91 V zeners at Z2/Z4 to extend display life
• Parts for rebuilding the System 3-7 display supply

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