Resets or failure to boot with good voltages at the solenoid driver board.

Resets from a bad MPU J4 power connector

Cause: MPU J4 sits in the battery corrosion zone and develops resistance. Corrosion can also bridge the neighbouring 43 V and 5 V pins, even under the header's plastic, sending 43 V into the 5 V logic and destroying the board.

Checks

• MPU TP1 should be 4.9-5.25 V and not lower than SDB TP1/TP3.
• MPU TP2 should be 12-16 V, matching SDB TP5; MPU TP3 should be 43 V.
• MPU J4 pins: 16 and 17 +5 V, 12 for 12 V, 15 for 43 V, 18 and 19 ground.

Fix

• Replace the J4 header and housing pins and clean any corrosion, including under the header.

This check is done with the game on; keep fingers off the line-voltage wiring and the high-voltage display circuit.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• MPU U9 voltages that show a working reset section
• MPU boots only some of the time
• Replacing the MPU reset section with a DS1811
• MPU LED locked on with no flicker: likely causes
• Testing the MPU reset circuit at U9 pin 40
• MPU stops before the seventh flash: check the 43 V at R113
• MPU stops after 7 flashes unless the top saucer coil is unplugged: bad driver chip
• No seventh MPU flash with a good solenoid fuse

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