The CPU board does not boot (displays never light after 5 seconds).

Dead CPU board: first checks

Cause: Battery corrosion, missing logic voltages or an open slam switch, before any chip fault.

Checks

• Look for corrosion, especially around Z6/Z7 (right of the battery) and Z8/Z28 (left of it); continuity-check traces after repairs.
• C16 (top cap by J1) should show 4.95 to 5.2 V; C17 below it about -12 V.
• Displays lighting at once and strobing means an open slam switch.

Fix

• Fix corrosion and voltages first, defeat the slam switch, then set the DIP switches to a known state before deeper tests.

Systems

• Gottlieb System 1

Related tips

• Using an LED to see a bench CPU boot
• CPU board clock check
• CPU address and data line check
• Aftermarket System 1 CPU boards
• Check the TC3 jumper plug on the CPU board
• Powering a System 1 CPU board on the bench
• The six Rockwell "spider" chips on the CPU board
• Testing CPU input buffers Z29 and Z27

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