Flicker and four flashes, then the sequence stops. The flipper relay normally clicks around the fifth flash.

Four flashes only: U11 PIA, R134 or a bad display

Cause: U11 6821 PIA or its socket, a bad resistor on U11 such as R134, or a faulty score display pulling the test down.

Checks

• With power off, unplug all score displays, then reconnect them one at a time (power off each time) and reboot to find a display that stops the count.

Fix

• Replace U11 or its socket, R134, or the bad display.

Systems

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

Related tips

• Three flashes only: U10 PIA
• One PIA output does not toggle in the test EPROM test
• Keep spare 6800, 6821 and 5101 chips
• CPU flickers then gives three flashes: bad PIA at U10
• Segments missing or stuck on: CPU board PIAs 9B and 7B
• Leon code running but LEDs dark: bad CPU PIA IC18
• Displays out, flippers and ball eject dead after display glitches
• One flash only: U7 6810 RAM

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