Test solenoid driver transistors with the game off

Steps

• Switch the game off; the board can stay in the game.
• Set the meter to diode test and put the black probe on the transistor's metal tab.
• Red probe on the centre leg: expect about zero.
• Red probe on each outer leg in turn: expect 0.4 to 0.6 V on both.
• Any other reading means the transistor should be replaced.

Systems

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

Related tips

• Solenoid driver board: transistor, diode, resistor and connector for each driver
• AS-2518-16 and AS-2518-22 solenoid driver boards interchange
• Test the 1N4004 diode behind a driver transistor
• Test the CA3081 pre-driver array
• Replace SE9302 drivers with TIP102, and renew the parts around them
• Solenoid driver board J3 pin functions
• Check the wire from a coil back to the solenoid driver board
• The solenoid driver board also carries the 190 V display supply

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