The 80B alphanumeric displays are blank or partly lit.

System 80B alphanumeric displays dark: check the display board supply

Cause: A fault in the display board's own high-voltage section, which turns 32 V AC from A4J1 pins 3-4 into -45 V and -15 V DC.

Checks

• Check bridge diodes CR1-CR4 (1N4004).
• Check zener VR1 (1N4737A, -45 V) and VR2 (1N4744A, -15 V).
• Check R1 (1k 2 W) and R2 (10k), which run hot, plus R3 (22k), R4 (10k) and R5 (3k).
• Buffers Z1 and Z2 (7417) rarely fail: the same signal should appear on their inputs and outputs.

Fix

• Replace the failed diode, zener or resistor.

The 80B display board turns 32 V AC into -45 V and -15 V DC; switch off before touching it and probe carefully with the power on.

Systems

• Gottlieb System 80B

Related tips

• No score displays light at all
• High-voltage input fuse FU2 blows
• System 80 switch matrix diodes
• Chime coils used with System 1 must be 12 ohms or more
• Electronic spares worth keeping for System 11 boards
• Rebuilding the +100 V section of the power supply
• Rebuilding the -100 V section of the power supply
• Game reboots when the flipper buttons are pressed

Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part Two, Clay Harrell (pinrepair.com)