Rectifier board TP3 reads no +12 V DC, or F3 blows as soon as the game is switched on.

No 12 V at rectifier TP3 even with a good F3

Cause: Missing 12 V AC from the transformer, or a failed bridge rectifier BR2.

Checks

• Measure AC volts between test points E11 and E12 on the rectifier board; expect about 12 V AC.
• No AC: check the transformer wiring and the transformer.
• AC present but no DC at TP3: BR2 is open.
• F3 blows instantly at power-on: BR2 is shorted.

Fix

• Replace bridge BR2, or repair the transformer feed.

Measure with care: the rectifier board has mains and high-voltage circuits nearby.

Systems

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

Related tips

• Rectifier board test points
• Route of the +12 V supply to the MPU and 5 V regulator
• No +12 V at rectifier board TP3
• Rectifier board J1 (to playfield) pins
• Rectifier board J2 (to cabinet) pins
• Rectifier board J3 (to backbox boards) pins
• Finding the coil that blows F4 (and stops the last flash)
• Rectifier board fuse ratings (all Bally 1977-1985)

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