One display misses the same segments on all digits, or every display shows wrong values (for example odd digits only in display test).

All displays show strange scores (one bad decoder)

Cause: A bad MPS-A42 segment driver or MC14543 decoder; one bad decoder on any display can corrupt the shared data for all of them.

Checks

• First rule out MPU J1 and the display header joints.
• Power off, unplug all but one display and check scores; add displays back one at a time (power off each time) until the fault returns.

Fix

• Replace the segment transistor, then the MC14543 (in a socket) on the offending display.

Systems

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

Related tips

• One segment never lights on a display
• Same digit missing or stuck on every display
• One digit missing on a score display
• Score display digit parts by position
• All 7-digit displays show a dim first digit and comma
• Flickering score displays
• Replace a score display glass
• Bally and Stern score display boards

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