A known-good U4 or U5 spider chip was fitted but the CPU board still misbehaves.

Swapped U4 or U5 spider still does not work

Cause: U4 and U5 together hold the operating system, so their revisions must match.

Checks

• Read the suffix on both chips.

Fix

• Pair them as A1753-CC with A1752-CD, A1753-CE with A1752-CF, or A1753-EE with A1752-EF.

Systems

• Gottlieb System 1

Related tips

• The six Rockwell "spider" chips on the CPU board
• Socketing a replacement spider chip
• CPU board clock check
• Spare chips for System 1 boards
• Aftermarket System 1 CPU boards
• Check the TC3 jumper plug on the CPU board
• Powering a System 1 CPU board on the bench
• Checking the U4 solenoid spider with a coin tune

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