Find a shorted display glass that blows F1

Steps

• Game off. Unplug every display glass from the master display board.
• Fit a new F1 of the correct 1/4 A slow-blow rating (never a bigger one).
• Switch on. If F1 holds, switch off and plug in one display.
• Repeat, adding one display each time, until F1 blows: the last one added is shorted.
• Replace it and check the UDN chips.

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

• All score displays dead
• Bottom segments missing and master display resistors burning: shorted display glass
• Upgrade R2/R5 and check R1/R4 in the display supply
• Master display board versions
• Which UDN6184 drives which display
• UDN display driver chips
• Using a logic probe on the display board safely
• Lower the display voltage to 91 V to extend display life

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