When replacing the large C23 filter capacitor, the old cap and its wire colours seem to be fitted the opposite way to the + mark on the board.

Replacing C23 on a Bally/Stern solenoid driver: follow the board's + marking

Cause: Wire colours and old repairs can mislead; the board marking is what matters. Tracing the + side back leads to the unregulated supply test point.

Checks

• Trace the + pad on the board back to the unregulated test point and the + side of the other filter cap.
• Check which lead of the new cap has the negative stripe.

Fix

• Fit the new capacitor with + to the board's + mark and the striped (negative) lead to ground, then refit the board and check the regulated voltages.

Large filter capacitors can hold a charge; unplug the game and let them discharge before working on the board.

Systems

• Bally MPU AS-2518-35

Related tips

• Check the wire from a coil back to the solenoid driver board
• Test solenoid driver transistors with the game off
• AS-2518-16 and AS-2518-22 solenoid driver boards interchange
• Solenoid driver board J3 pin functions
• The solenoid driver board also carries the 190 V display supply
• Solenoid driver board: transistor, diode, resistor and connector for each driver
• Rebuild the solenoid driver board high-voltage section
• Flippers weak or intermittent from the solenoid driver board

Source: Pinball Repair help group!! (Facebook group)