Rebuild the solenoid driver board high-voltage section

Steps

• Replace all the semiconductors and capacitors even if they test good, because these parts fail in pairs: Q21 2N3584 (250 V, 2 A, TO-66), Q22 and Q23 2N3440 (250 V, 1 A, TO-39), VR1 1N5275A zener (140 V, 1 W), CR21 1N4004, and C27/C28 0.01 uF 400 V metal polyester.
• Replace the RT1 25K trim pot, which is poor quality, and fuse F1 (3/16 A fast-blow) where fitted.
• Check every resistor and replace any more than 5% off or open: R51 22K 1/2 W and R56 82K 1/2 W (both often burned), R55 1.2K, R54 8.2K, R52 390 ohm (all 1/4 W) and R35 100K 1 W.
• Mount the new resistors and transistors slightly off the board for airflow, reusing the transistor spacers (page 47).
• Check all the transistors again before power-on, since one failure takes out the others in this direct-coupled circuit.

The solenoid driver / regulator board makes about 190 V DC for the score displays (around 230 V on some Stern boards); a shock from it hurts. Work with the game unplugged and let the filter capacitors discharge, and use one hand and insulated probes for live checks.

Systems

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

Related tips

• Replace SE9302 drivers with TIP102, and renew the parts around them
• Rebuilding the solenoid driver board high-voltage section
• Where the display high voltage enters and leaves the solenoid driver board
• Rebuilding the +100 V section of the power supply
• Rebuilding the -100 V section of the power supply
• Power up and set a rebuilt high-voltage section
• High-voltage input fuse FU2 blows
• Test each lamp column driver with a test lamp

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