High voltage is present but the displays show nothing.

Displays have high voltage but stay blank

Cause: The blanking signal is low or not reaching the display circuits.

Checks

• Check CPU board connector 1J3, which carries blanking to the displays.
• Measure interboard connector pin 37: it should be 4 V or more.
• With the game off, clip pin 37 to +5 V and switch on. If the displays now light, the blanking circuit is at fault.

Fix

• Repair the blanking circuit or connector (see the dead CPU section of the guide).

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

• Score displays dead but digits glow: bad wire in the CPU blanking plug (1J3)
• Ball and credit displays show only even numbers after header work
• Seven-digit scoring on six-digit displays for green-ROM games
• CPU LEDs flash and go out but the score displays stay dark
• Digits burning or faint on players 1 and 3 (or 2 and 4)
• Whole digits missing
• Display completely dark with high voltage present
• "Adjust Failure" at power-on

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