Every score display is blank.

All score displays dead

Cause: Missing high voltage or +5 V from the power supply (often fuse F1 or the high-voltage section), or a low blanking signal.

Checks

• At power supply connector 3J5: pin 1 logic ground, pin 3 -100 V DC, pin 4 +100 V DC, pin 5 high-voltage ground, pin 6 +5 V DC.
• Check F1 (1/4 A slow-blow).
• Look for a faint orange glow at the corner of each display: it means high voltage is reaching the displays.

Fix

• If F1 is fine but a voltage is missing, rebuild the high-voltage section of the power supply board.
• If voltages are fine, check the blanking signal (next entry).

The display supply carries about 100 V DC (plus and minus); keep fingers and probes off the master display board and power supply high-voltage section with the game on.

Systems

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

Related tips

• Find a shorted display glass that blows F1
• One score display dead
• Display high voltage out of range
• Score displays light then dim or flicker
• Score displays weak, dim or dead with fuses good
• Score displays fade in a scrolling pattern
• A segment missing on a score display
• Score displays dead but digits glow: bad wire in the CPU blanking plug (1J3)

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