Test the coils behind the solenoid expander

Steps

• From the schematic, find the solenoid driver transistor that feeds the SEB coils.
• Boot the game and press the test button once for the lamp test.
• Clip a jumper to the backbox ground strap and hold the other end on that transistor's metal tab (page 38).
• The two coils on that driver should fire alternately in step with the flashing lamps.

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-2518-35

Related tips

• How the solenoid expander board doubles up coils
• No coils work at all
• The bulb next to the solenoid expander board must work
• Centaur uses its solenoid expander for the ball-to-playfield kicker
• How Bally coils are switched
• Drop target falls instead of the ball being kicked out (SEB games)
• Wrong coil fires or a coil never fires
• Expander-driven coils fire in pairs: drop target coil fitted without its second diode

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