The score displays, worst of all the credit/ball-in-play display, flicker. Cleaning the connector contacts helps only for a short time.

High-voltage score displays flicker: reflow the cracked joints at the display connector

Cause: The solder joints where the connector pins are soldered to the display board have cracked, from the wiring harness pulling on them and the head being opened and closed. The single-sided boards make this worse.

Checks

• Pull the worst display and look at the connector pin joints on the back with a magnifier or a phone camera; look for rings around the pins.

Fix

• Reflow every connector pin joint on the display with fresh solder.
• Do the same on the other displays, and on the MPU and driver board connector pins, before chasing other faults.

Bally displays run on high voltage (around 190 V DC). Switch the game off, unplug it, and let the high-voltage supply discharge before removing or handling a display.

Systems

• Bally MPU AS-2518-35

Games

• Star Trek

Related tips

• Garbled displays: broken pin in the MPU display connector
• One score display dark: poor contact at MPU J1 pin 20
• Score displays flicker and seem to scroll: weak high voltage, power board replaced
• Flickering score displays
• F2 blown, no display high voltage at TP2
• Displays strobe on early Bally SS: check the J3 ground pin for the HV circuit
• Bally 7-digit display misbehaves wherever it is fitted: replace the decoder chip
• Set the display high voltage to about 170 V

Source: Pinball Repair help group!! (Facebook group)