A bench CPU board stays completely dead.

CPU board reset circuit check

Cause: The reset line never goes high, so the CPU never starts.

Checks

• TC1 is the vertical white plug on the left and TC2 the one in the centre; pin 1 is at the top of each.
• TC1 pin 14 should be -12 V at power-on, switching to +5 V after about half a second.
• Z2 pins 7 and 9 should rise to 5 V about a second after power-on.

Fix

• Replace reset transistors Q5 and Q6 (MPS-A70).
• Then Z2 (4528 CMOS).
• Then caps C31 and C32 (0.1 mfd).

Systems

• Gottlieb System 1

Related tips

• Permanently defeating the slam switch on the CPU board
• The slam switch must be closed for the game to run
• Displays light at once showing zeros
• Powering a System 1 CPU board on the bench
• CPU board clock check
• CPU address and data line check
• Dead CPU board: first checks
• System 1 CPU board connectors

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