Displays may still work, possibly overly bright, but the glasses are burning and wear out quickly.

Displays burning too bright: HV regulator failed shorted

Cause: The HV regulator on the solenoid driver board has failed shorted and passes the full 220-230 V input straight to displays that need 155-190 V.

Checks

• Measure TP2 to GND (output, should be 155-190 V) and TP4 to GND (input, about 220-230 V).
• If TP2 reads the same as TP4, the regulator is dead (page 45). A TP2 reading of 230-250 V confirms it (page 46).

Fix

• Rebuild the high-voltage section promptly before the displays are ruined.

The solenoid driver / regulator board makes about 190 V DC for the score displays (around 230 V on some Stern boards); a shock from it hurts. Work with the game unplugged and let the filter capacitors discharge, and use one hand and insulated probes for live checks.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• High voltage still too high or too low after a rebuild
• The solenoid driver board also carries the 190 V display supply
• First checks before repairing Bally score displays
• Capacitor C26 holds the display high voltage after power-off
• Where the display high voltage enters and leaves the solenoid driver board
• All score displays blank with the MPU fully booting
• All displays dark after fitting a new power supply: blown solenoid driver board fuse
• Rebuild the solenoid driver board high-voltage section

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)