The 60 V and/or 42 V display supply is absent.

+60 V or +42 V display voltage missing

Cause: Bad rectifier diodes on the power supply, a blown bottom panel display fuse, or a shorted score display.

Checks

• Test the four 1N4004s on the power supply on diode range: 0.4-0.6 one way, nothing the other.
• Check the bottom panel display fuse even if it looks fine.
• Power off, unplug all but one display, power on and measure; repeat adding one display at a time.

Fix

• Replace bad diodes; replace a shorted display, which can also take out the CPU 7448 chips.

The display supply runs at 60 to 69 volts; work on it with the game off and never plug or unplug display connectors with power on.

Systems

• Gottlieb System 1

Related tips

• How the Gottlieb fluorescent displays work
• Score displays flicker or go dim
• Never plug displays with the power on
• Which CPU chips run the displays
• Reviving a faded Futaba display
• System 1 and System 80 six-digit displays interchange
• Display high-voltage section of the power supply
• Use C6 negative as ground when measuring 60/42 V

Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)