At switch-on the displays jump straight to 000000 and flicker in a sideways rolling pattern, and the start button is ignored.

Displays show 000000 at once and scroll; start does nothing

Cause: The normally closed slam circuit is open: the coin door slam switch, the ball roll (cage) tilt slam contact or a poor connection at CPU connector J5, which carries the slam line.

Checks

• Check the coin door slam switch is closed.
• Check the ball roll tilt assembly and its wiring.
• Reseat and inspect CPU connector J5.

Fix

• Repair the open switch or connector, or do the slam switch modification from Part One.

Systems

• Gottlieb System 80

Related tips

• Niwumpf replacement CPU board takes about 10 seconds to show scores
• Dead CPU board: check the reset line first
• First power-up, step 4: add the CPU board one connector at a time
• Replace the System 80 reset circuit with a DS1811 chip
• What the System 80 reset (watchdog) board does
• Why a System 80 CPU stops running
• Game won't boot, or keeps rebooting, because of the reset board
• Reset section zener VR1 burnt on a System 80 CPU board

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