Voltages are fine with the display connector off, but the high-voltage fuse blows as soon as it is reconnected.

High-voltage fuse blows once the display connector is plugged back in

Cause: A shorted display glass, or a shorted UDN6118 or UDN7180 driver on the master display board.

Checks

• Test the UDN chips for shorts with a meter on diode test (see the UDN test procedure).

Fix

• 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

• Score displays weak, dim or dead with fuses good
• Lower the display voltage to 91 V to extend display life
• Displays show only three or four digits at a time in a slow wipe
• Displays blank but the game plays
• System 9 versus System 11 display data
• UDN display driver chips
• Characters missing from a display
• Display board chips shown as 4050 are really 4049

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