The game does not boot although all fuses test good and are the right values; the MPU LED stays solid instead of blinking.

Game does not boot, fuses fine: loose A1-J1 power connector on the MPU

Cause: The power connector into the MPU (A1-J1, from the power supply) was loose and not making good contact.

Checks

• Check each connector on the MPU for a firm fit; wiggle A1-J1 and look for loose or burnt pins.
• Compare the MPU LED with what the manual says it should do at power-up.

Fix

• Repin or re-crimp A1-J1 so it grips the header firmly; the game then booted and played.
• Remove the old battery and clean up any acid damage on the MPU while it is out.

Systems

• Gottlieb System 3

Games

• Big House

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