Test the 1N4004 diode behind a driver transistor

Steps

• Switch off and take the solenoid driver board out.
• On diode test, measure across the CR diode noted from the schematic, then reverse the leads. In-circuit, both directions read about 0.4 to 0.6 V.
• For a sure result, lift one diode lead: one direction should read 0.4 to 0.6 V and the other open.
• Replace the 1N4004 if the readings differ.

Systems

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

Related tips

• Solenoid driver board: transistor, diode, resistor and connector for each driver
• Test solenoid driver transistors with the game off
• Fire a coil by grounding its driver transistor tab (game on)
• 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
• Test the coils behind the solenoid expander
• BUX84 as a substitute for the 2N3584 HV transistor

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