Score displays dark; F2 is blown and TP2 reads nothing, or F2 blows at power-on.

F2 blown, no display high voltage at TP2

Cause: One of the four 1N4004 diodes CR1-CR4 next to F1 is shorted.

Checks

• Test each diode on the meter's diode range: 0.4 to 0.6 V one way, open the other.

Fix

• Replace all four with 1N4007, banded ends the same way as the originals.

The score display supply runs at 170-230 V DC; keep hands off the rectifier and driver boards with power on.

Systems

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

Related tips

• All score displays blank with the MPU fully booting
• All displays dark after fitting a new power supply: blown solenoid driver board fuse
• Arcing between J3 pins on the solenoid driver board and displays out
• No voltage at any rectifier board test point: burnt mains wire to the transformer
• No +12 V at rectifier board TP3
• No feature lamp voltage at TP1 (-18 board)
• Capacitor C26 holds the display high voltage after power-off
• Only the knocker fires and the lower playfield GI is out: replace the rectifier board

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