One segment (for example a lower segment on one player's display) never lights.

A segment missing on a score display

Cause: Most often a burnt 10k 1/2 W resistor among R1-R14 on the master display board; otherwise a bad UDN7180 or a broken lead into the glass.

Checks

• Measure R1-R14 in circuit; replace any more than 10% off 10k.

Fix

• Replace the resistor; if it burns again, suspect the glass.

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

• Whole digits missing
• Four digits missing on the player 2 and 3 displays: bad driver IC12 on the master display
• Bottom segments missing and master display resistors burning: shorted display glass
• All score displays dead
• One score display dead
• Missing segments: check the UDN7180 with a probe
• Master display board versions
• Which UDN6184 drives which display

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