One or more displays flicker.

Flickering score displays

Cause: Most often cracked solder at the display's .156" J1 header (usually the end pins 1-6 and 14-20). Less often display glass pin 36, R21, R22, R29, Q17, an open C2 or U1 pin 13. If all displays flicker, the MPU (usually PIA U10, near the battery) or a corroded trace to it.

Checks

• With the game on, press gently on the display connector housing; if the flicker stops, the header joints are cracked.
• Inspect the other listed parts on a single flickering display.
• For all displays flickering, check U10 and the traces around the battery area for corrosion.

Fix

• Reflow every display's J1 header with fresh solder; reflow or replace the other parts as needed.

Systems

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

Related tips

• Replace a score display glass
• Bally and Stern score display boards
• One digit missing on a score display
• Score display J1 to MPU J1 connections
• Score display digit parts by position
• Score displays dim
• First checks before repairing Bally score displays
• One or two score displays completely blank

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