A display does not work even after moving it to another player position (or all are blank).

A display not working from MPU or sound board faults

Cause: Data not reaching the displays, often from MPU chip U20; a faulty sound board can also blank all the displays (page 62).

Checks

• Move displays between positions to rule out the glass.
• Unplug every connector from the sound board and retest.

Fix

• Replace U20, or repair the sound board.

Systems

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

Related tips

• Bally -35: same digit positions dark on every display: open digit drive resistors
• One score display dark: poor contact at MPU J1 pin 20
• Only even-numbered score displays show numbers
• All score displays blank with the MPU fully booting
• Score display J1 to MPU J1 connections
• All digits on all displays show 2s or 7s
• All displays strobe or flash rapidly
• First checks before repairing Bally score displays

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