On every display the leading digit and the comma after it glow dimly whenever the displays are on.

All 7-digit displays show a dim first digit and comma

Cause: One display module loading the lines, or an MPU fault: a poor J1 connection, U20 or PIA U11.

Checks

• Disconnect the displays one at a time (power off each time) to see if one causes it.
• Inspect MPU J1, swap U10 and U11, and check the display high voltage is 155-190 V.

Fix

• Replace the faulty display board part, repin J1, or replace U20 or U11.

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-2518-35

Games

• Xenon

Related tips

• All digits on all displays show 2s or 7s
• Same digit missing or stuck on every display
• One digit missing on a score display
• Seven-digit and six-digit displays
• Score display digit parts by position
• One segment always lit on a display
• Score displays dim
• All displays show strange scores (one bad decoder)

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