Power up and set a rebuilt high-voltage section

Steps

• Turn the HV pot fully counter-clockwise (minimum).
• On later boards with an HV fuse, leave that fuse out for the first power-up.
• Power on, measure TP2 and set it to about 170 V or lower.
• Switch off and give the high voltage a couple of minutes to bleed away, then fit the 3/16 A F1 fuse.
• Power on and press the test button twice for the display test; let it run several minutes, then recheck TP2.

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

• Rebuild the solenoid driver board high-voltage section
• Capacitor C26 holds the display high voltage after power-off
• Set the display high voltage to about 170 V
• Where the display high voltage enters and leaves the solenoid driver board
• High voltage still too high or too low after a rebuild
• All displays dark after fitting a new power supply: blown solenoid driver board fuse
• The solenoid driver board also carries the 190 V display supply
• Displays burning too bright: HV regulator failed shorted

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