The game will not boot. After repairs to the original board, a new CPU board, new processor and new PIAs, it still does not boot.

Won't boot even with a new CPU board and new chips: the new ROMs were bad

Cause: The newly bought game ROMs were faulty, so every board tried was running bad code.

Checks

• Fit a test EPROM (diagnostic ROM) to confirm the CPU board itself works.
• If the board passes with the test ROM, suspect the game ROMs, even brand new ones: verify them in an EPROM programmer against the correct image.

Fix

• Replace the game ROMs with verified good ones (the original poster burned new EPROMs with a programmer).

Systems

• Williams System 11B

Games

• Black Knight 2000

Related tips

• Won't boot after restoration, new EPROMs fitted: try the original ROMs
• MPU won't boot even though a test ROM passes every PIA and RAM: bad game ROMs
• Resets continue after diode repair: power and connector checks
• Occasional U10 PIA error at power-on, but the game plays
• Game will not boot consistently: power-on reset (POR) circuit
• Game will not boot after sitting off, but starts on the second try
• CPU keeps resetting: reset line at U15 pin 40
• Displays lose digits and coils buzz once the game warms up

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