The negative voltages read low (for example -102 and -93 V) and the display is very dim, even after an HV rebuild.

Negative HV low and display barely lights

Cause: Drifted resistors in the HV section: R6 (R26 on WPC-95, 47k ohm) open, or R4 (R30 on WPC-95, 120 ohm) reading high.

Checks

• Lift one leg of each resistor and measure it out of circuit.

Fix

• Replace the out-of-spec resistors; in the example the voltages rose to -112 and -100 V and the display was bright again.

High voltage section: work with the game unplugged.

Systems

• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Display voltages low: display or HV section?
• -125 V and -113 V read the same and the display is dark
• The two negative display voltages must be 12 V apart
• +5 V or +12 V missing at the display
• Dot matrix display supply voltages
• Gas discharge displays need high voltage
• +62 V reads over 70 V
• Dot matrix display power connector pinout and voltages

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Three, Clay Harrell (pinrepair.com)