Diagnostics run without the game PROM

Because the audit and test code lives in the spider chips, a CPU board boots and runs all audits and tests with Z23 empty; only starting a game locks it up.

Systems

• Gottlieb System 1

Related tips

• Using the "T" test PROM
• The Z23 game PROM
• 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

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