MPU TP2 has no +12 V and the LED is dark.

No +12 V at the MPU: check the rectifier board

Cause: Blown 12 V fuse F3 or burnt fuse clips on the rectifier board, then the bridge or transformer feed.

Checks

• Measure rectifier board TP3 for about +12 V DC.
• Pull fuse F3 (4 A) and test it for continuity; look at its clips for heat damage, which is common.

Fix

• Replace F3 and any discoloured or loose fuse clips.

The rectifier board carries mains and high voltage; switch off and unplug the game before touching it.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• MPU LED lit solid: check +5 V first
• 12 V at the rectifier board but not at the MPU
• Rectifier board test points
• MPU locks with LED on because of C23 or Q20 on the solenoid driver board
• Route of the +12 V supply to the MPU and 5 V regulator
• MPU LED never lights at all
• Solenoid driver TP1 below 5 V with TP5 normal
• A missing test point voltage: what to check first

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)