The game behaves strangely, especially after a long time switched on.

Erratic play after the game has been on a while

Cause: The bipolar game PROM at Z23 overheating.

Fix

• Glue a small heatsink onto the PROM; worth doing anyway to extend its life.
• Or replace it with a 2716 EPROM on an adaptor.

Systems

• Gottlieb System 1

Related tips

• Spare chips for System 1 boards
• The six Rockwell "spider" chips on the CPU board
• Which spider chips fail and why
• Swapped U4 or U5 spider still does not work
• Check the TC3 jumper plug on the CPU board
• Odd high scores usually mean a bad 5101 RAM
• Aftermarket System 1 CPU boards
• Dead CPU board: first checks

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