Score displays flicker (especially playfield-mounted ones) and pop bumpers act up or don't work.

Flickering displays and erratic pops from a poor J3 ground

Cause: Worn round pins at power supply connector J3, which carries the display voltages and display grounds.

Fix

• Replace J3's header with .156" square pins (26-48-1125) and the 7-pin plug with a new housing and Trifurcon pins (08-52-0113).
• As a quick alternative, run a wire from J3 pins 4/5 to the power supply frame (sand the paint where it lands).

J3 carries the 42 V and 60 V display supplies; work on it with the game off.

Systems

• Gottlieb System 80
• Gottlieb System 80A

Related tips

• Score displays flicker
• The display voltages to check
• System 80 schematics' 'offset' voltages are DC bias for the display filaments
• 60 V and 42 V disappear when the displays are connected
• Coils lock on and burn because of the Gottlieb ground fault
• Ground mod step 1: CPU board ground wire
• Diode-test the PMD10K40/2N6057/2N6059 on the pop board or power supply
• Tie the 80/80A power supply logic ground to its heat sink plate

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