Intermittent or lost grounds on an 80B game.

System 80B ground lost at the transformer panel plugs

Cause: The 9-pin plugs with white ground wires on the side of the transformer panel use small boards bolted to the frame whose pin solder joints crack, dropping that wire's ground.

Checks

• Unplug them, remove the two 1/4" hex bolts holding each pin board and inspect the back for cracked joints.

Fix

• Reflow the pins.
• Better still, join all the ground wires together before the plug so one bad pin no longer matters, or replace the plugs with ring or spade terminals bolted to the frame.
• On versions with screw or terminal-strip grounds, make sure each is tight.

Systems

• Gottlieb System 80B

Related tips

• System 80 games have no surge protection on the line input
• First power-up, step 1: check the bottom-panel fuses
• Quick diode test of a bottom-panel bridge rectifier
• Identifying the leads of a bottom-panel bridge rectifier
• Check the 80B bottom-cabinet 10,000 mfd filter capacitor
• A bottom-panel fuse blows the moment the game is switched on
• System 80 board "A" numbers
• Tools for repinning System 80 connectors

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