After the game has been on for a while (and eventually within seconds of power-on), the digits on the displays start flickering and then disappear.

Display digits flicker then vanish after the game warms up: poor board connector contact

Cause: Poor contact at the board connectors; members pointed at fractured joints on the MPU's J1 display header (top pins especially) and the display headers.

Checks

• Reflow the .156 header pins on the displays.
• Check the MPU J1 .100 header for cracked joints.
• Reseat every board connector and see if the fault clears.

Fix

• Reseat the connectors as a first step; for a lasting repair, reflow or replace the MPU and display header pins and repin the plugs.

Bally displays use about 190 V DC. Power off before handling the display connectors.

Systems

• Bally MPU AS-2518-35

Games

• Paragon

Related tips

• Four switches on one return line dead with good wiring: failed 6821 PIA on the MPU
• Only GI lights and MPU LED never flashes: loose wiring at J3 on the solenoid driver board
• Background sound works in test but not in games: check DIPs 29-30, then reseat connectors
• Controlled lamps stuck or not flashing: reflow MPU and lamp driver header pins
• MPU stops before the 7th flash until sound board power is unplugged: replace CR3
• Bally MPU loops through its 7 flashes and resets: check R134 and the interrupt traces
• Only three players allowed on an aftermarket MPU: reseat J1, clear memory, reset DIPs
• No background music, only target sounds: set feature adjustment 18 to 03

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