Player 1's display stays dark. Swapping displays shows the fault stays with the position, and the display high voltage is fine.

One score display dark: poor contact at MPU J1 pin 20

Cause: Each display has its own enable signal (display pin 15) that is not daisy-chained like the rest; for this display it passes through MPU connector J1 pin 20, which had a poor contact.

Checks

• Swap displays to see whether the fault follows the display or the position.
• Check the high voltage and set it to spec.
• Trace the dead display's pin 15 back to the MPU and check its connector pin.

Fix

• Clean and repin the bad pin at MPU J1 (pin 20 here) so the enable signal gets through.

The display supply is high voltage (about 175 V here); keep fingers off the display boards and high voltage section with the game on.

Systems

• Bally MPU AS-2518-35

Games

• Supersonic

Related tips

• A display not working from MPU or sound board faults
• Bally -35: same digit positions dark on every display: open digit drive resistors
• Only even-numbered score displays show numbers
• Score display J1 to MPU J1 connections
• All score displays blank with the MPU fully booting
• Flickering score displays
• All digits on all displays show 2s or 7s
• First checks before repairing Bally score displays

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