The game powers up with scrambled dots on the display, the A8 LED is on solid, and the CPU may not boot properly.

Garbage on the dot matrix at power-on

Cause: U8, the custom programmed GAL on A8, is a common failure, nearly always caused by plugging or unplugging A8 or the display with power on.

Checks

• See whether the A8 LED is flashing or stuck on.

Fix

• Fit a programmed U8 GAL.
• Always power off before touching A8 or display plugs.

The A8 controller makes roughly +62 V, -100 V and -112 V for the display; keep hands off it with power on.

Systems

• Gottlieb System 3

Related tips

• DMD controller LED stays on
• Dot matrix dark: +62 V missing
• The A8 dot matrix controller board
• Display voltages the A8 board should supply
• Never hot-plug the A8 board or the display
• Rebuilding the A8 high-voltage section
• Nonsense message at boot, game stuck in a loop
• A5, A6, A8 and A20 plug identification

Source: Repairing Gottlieb System 3 Electronic Pinball Games from 1989 to 1996, Clay Harrell (pinrepair.com)