A System 6 game will not boot correctly. Both the built-in diagnostics and a test ROM report a bad 5101 RAM, even though the 5101 has already been replaced and the buffers, inverters and CPU are new.

System 6 won't boot and fails the 5101 RAM test even after replacing it: bad 5101 stock

Cause: The replacement 5101 was itself bad; fake or remarked 5101 chips are common, even from pinball parts shops.

Checks

• Run the game's own diagnostics with the coin door open (the memory protect interlock must be released or the 5101 test fails by design).
• Look closely at the 5101's markings; remarked chips sometimes show scraped or rubbed-off printing.

Fix

• Fit a 5101 of a different brand from a different, trusted source. Here the new chip passed both the built-in and the test ROM checks.
• Some members suggest a newer test ROM, since an older popular one only checks part of the 5101.

Systems

• Williams System 6 / 6A

Related tips

• Boots into audit mode every power-up with good batteries: bad 5101 RAM
• Leon's test EPROM fitted but the LEDs do not start flashing
• Game keeps resetting: replace the 5101 RAM (an NVRAM works)
• Game powers up in audit mode instead of attract mode
• 5101 RAM at U8 fails often; speed matters
• Two flashes only: U8 5101 RAM
• Odd high scores usually mean a bad 5101 RAM
• Locks up when a second game is started: bad 5101 RAM

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