Ground mod step 1: CPU board ground wire

Steps

• Find electrolytic capacitor C1 just right of CPU power connector A1-J1.
• Solder about 12" of wire to its negative (top) lead and crimp a fork terminal on the other end.
• On 80/80A, bolt it under a mounting bolt of the power supply heat sink plate, sanding off the black finish where it lands. On 80B, take it to the ground plane screw at the lower right of the backbox.
• On 80/80A, if the power supply board ground jumper was not done, also wire the power supply's large C1 negative lead to its metal frame.
• Continue from the power supply plate to the metal lock plate at the upper left of the backbox, which has Gottlieb's green wire to the copper ground bus by the transformer; an extra wire straight to that bus (sanded clean) is optional.
• Check the bare 6 V GI wiring does not touch the power supply frame on games where it runs close.

Systems

• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B

Related tips

• Ground mod for the System 80B power supply
• Ground mod step 4: double the +5 V and ground pins between CPU and driver boards
• First power-up, step 3: run the power supply on its own
• Tie the 80/80A power supply logic ground to its heat sink plate
• Which System 80 power supply boards are interchangeable
• Original 80/80A power supply design overheats CR7
• System 80B +5 V drifts or jumps
• Bench-test an 80/80A power supply in the game, part 1

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