A new replacement CPU board, fitted with the game's own processor and EPROM, does not boot. +5 V and +18 V are present and two status LEDs stay on.

Replacement CPU board won't boot with the old processor: socket contact

Cause: The processor was not making good contact in the new board's socket, which was a different style from the original; no pins were bent.

Checks

• Check the EPROM size jumper matches the game ROM.
• Check the board is screwed down so it is grounded to the backbox.
• Swap the processor with one from a known working board to see whether the fault follows the chip or the board.

Fix

• Reseat the processor firmly, or swap processors; once each sat in a socket where it made good contact, both boards booted.

Systems

• Data East CPU Version 3

Games

• Last Action Hero

Related tips

• CPU EPROM jumpers J4 and J5
• All lamps come on, flipper fuse blows and the game won't boot: failed replacement NVRAM
• CPU jumpers J4 and J5 set the EPROM size at 5C
• Data East CPU diagnostic test EPROM
• CPU still will not boot after the basics
• Leon's Data East CPU test EPROM
• New CPU board locks up when the coin door buttons are plugged in: reseat the PIA
• Test program does not run at all

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