No score displays; the display fuse (or one of two on later games) on the power supply board is blown.

Blown high-voltage display fuse in the backbox

Cause: A failed high-voltage section on the power supply, a shorted display glass, or a shorted UDN6118/UDN7180 on the master display board.

Checks

• Unplug the high-voltage output connector (3J5 or 3J2), fit a new fuse and power on.
• If the fuse blows with the connector off, the power supply high-voltage section needs rebuilding.
• If it holds, reconnect but unplug every connector to the master display board and try again; if it still holds, a UDN chip or a display glass is shorted.

Fix

• Rebuild the high-voltage section, or replace the shorted UDN chip or display glass.

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 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Power supply board fuses (typical game)
• Half the backbox lamps and the lower displays dead: check the backbox fuses
• Score displays weak, dim or dead with fuses good
• Display voltages at 3J5, power supply D-8345 (High Speed to Swords of Fury)
• Routine high-voltage changes on every System 11 power supply
• Display voltages at 3J2, power supply D-11883/D-12246 (Taxi to Dr. Dude)
• High-voltage fuse blows once the display connector is plugged back in
• High-voltage supply rebuild parts, System 3 to 11C

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