Finding the coil that blows F4 (and stops the last flash)

Steps

• With power off, unplug the playfield solenoid connectors from the solenoid driver board (the ones on the left side and the one at bottom right).
• Fit a new F4 and power up; the MPU should now finish its flashes.
• Power off, refit one connector, power on. Repeat until F4 blows; the last connector refitted leads to the fault.
• Look at that group: watch which coil pulls in at power-on, or lift one coil wire at a time, until the fuse stops blowing.
• The fault is then the coil, its diode or its driver transistor.

Systems

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

Related tips

• Coil locks on at power-up and gets hot
• Every flash but the last one
• Game locks up after the seventh flash
• Solenoid driver board: how the MPU selects a coil
• No 12 V at rectifier TP3 even with a good F3
• Use the solenoid test to find a coil that does not fire
• Solenoid driver/regulator board test point voltages
• Solenoid driver TP5 under 13 V

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