The CPU board never boots (no display at power-on), even though +5 V is present.

Dead CPU board: check the reset line first

Cause: The reset circuit by the battery is the part most often damaged by leakage. It should hold the 6502's reset pin 40 at 0 V for roughly 100 ms after power-on and then raise it to 5 V; if it never goes high the processor never starts.

Checks

• Feed +5 V to the board through its left-hand 5-pin power connector.
• Measure 6502 pin 40: 5 V means reset is working; 0 V means it is not.
• With reset working, check the clock circuit next, which sits just below crystal Y1.

Fix

• Repair the reset circuit (battery corrosion kit parts, or the DS1811 conversion).

Systems

• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B

Related tips

• First power-up, step 4: add the CPU board one connector at a time
• Game won't boot, or keeps rebooting, because of the reset board
• Reset section zener VR1 burnt on a System 80 CPU board
• What the System 80 reset (watchdog) board does
• Why a System 80 CPU stops running
• Replace the System 80 reset circuit with a DS1811 chip
• Niwumpf replacement CPU board takes about 10 seconds to show scores
• Displays show 000000 at once and scroll; start does nothing

Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part One, Clay Harrell (pinrepair.com)