With an aftermarket (Alltek) MPU set for this game, it will only accept and play three players; set to another game's code, four-player games work.

Only three players allowed on an aftermarket MPU: reseat J1, clear memory, reset DIPs

Cause: A poor J1 connection at the MPU and leftover settings from the code previously selected on the board.

Checks

• Swap displays between positions to rule out the fourth display.
• Check the aftermarket board's instructions for the exact memory-clear and game-select sequence when changing game codes.

Fix

• Reseat (and later repin) MPU connector J1, clear the board's memory, then set the DIP switches for this game again.

Systems

• Bally MPU AS-2518-35

Games

• Eight Ball Deluxe (LE)

Related tips

• Bally MPU loops through its 7 flashes and resets: check R134 and the interrupt traces
• Four switches on one return line dead with good wiring: failed 6821 PIA on the MPU
• Background sound works in test but not in games: check DIPs 29-30, then reseat connectors
• Only GI lights and MPU LED never flashes: loose wiring at J3 on the solenoid driver board
• 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
• No background music, only target sounds: set feature adjustment 18 to 03
• Display digits flicker then vanish after the game warms up: poor board connector contact

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