The score displays show garbage.

Garbled displays: broken pin in the MPU display connector

Cause: A broken pin in the MPU connector that carries the display data, plus corroded contacts on the player 1 display plug.

Checks

• Reseat the MPU's display connector with the game off and see if the displays change.
• Unplug displays one at a time to see if one display is dragging the others down.
• Inspect each pin of the display connectors.

Fix

• Repin the broken connector pin and clean or repin the corroded display plug.

Systems

• Bally MPU AS-2518-35

Games

• Star Trek

Related tips

• High-voltage score displays flicker: reflow the cracked joints at the display connector
• Score display J1 to MPU J1 connections
• One score display dark: poor contact at MPU J1 pin 20
• Only even-numbered score displays show numbers
• LE: new LED score displays miss a digit or show zeros: pins 2 and 11
• Flickering score displays
• Replace a score display glass
• No score displays light at all

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