Score displays are dim, barely lit or dark, and the high-voltage fuses are not blown.

Score displays weak, dim or dead with fuses good

Cause: The 39k resistors R1 and R4 in the power supply high-voltage section drift high or open, starving the +100 V and/or -100 V display supplies.

Checks

• Game off: measure R1 and R4 with an ohmmeter.
• Measure the +100 and -100 V outputs at the power supply display connector.

Fix

• Replace R1 and R4 with flame-proof 39k resistors, 1 or 2 W, mounted slightly off the board for cooling. Replace them even if they test good.
• Do this before buying display glass; a dim display often comes back fully.

The display supply runs at about 100 V DC (plus and minus) with large filter capacitors; work with the game off and unplugged, and measure live only with insulated probes.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7
• Williams System 9
• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Display high voltage out of range
• All score displays dead
• Score displays light then dim or flicker
• High-voltage fuse blows once the display connector is plugged back in
• Score displays fade in a scrolling pattern
• Upgrade R2/R5 and check R1/R4 in the display supply
• Displays blank but the game plays
• Fit 91 V zeners at Z2/Z4 to extend display life

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell