Fire a coil by grounding its driver transistor tab (game on)

Steps

• With the game in attract mode, clip a jumper lead to ground in the backbox.
• Briefly touch the other end to the metal tab of a driver transistor; its coil should fire (page 20).
• Alternatively touch the U chip pin for that driver that does not go to the diode.
• This proves the path from board to coil, not the transistor. If the transistor tests good and the coil does not fire, check the playfield fuse and the wiring and connector to that coil.

This check is done with the game on; keep fingers off the line-voltage wiring and the high-voltage display circuit. Touch only briefly so the coil is not held on.

Systems

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

Related tips

• Test the 1N4004 diode behind a driver transistor
• Solenoid driver board: transistor, diode, resistor and connector for each driver
• Test the CA3081 pre-driver array
• AS-2518-16 and AS-2518-22 solenoid driver boards interchange
• Replace SE9302 drivers with TIP102, and renew the parts around them
• One coil dead with a good transistor and power at the coil
• No coils work at all
• How Bally coils are switched

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