The dot matrix stays dark because the +62/+64 V display supply is gone.

Dot matrix dark: +62 V missing

Cause: The small 2N5551 transistors Q1 and Q2 in the A8 high-voltage section have blown, usually after the display plug was moved with power on (which can also kill U8).

Checks

• Measure the display supplies at A8J2 with the game on.
• Test Q1, Q2 and the rest of the high-voltage parts power off.

Fix

• Rebuild the high-voltage section (see the rebuild parts list).

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

• The A8 dot matrix controller board
• Display voltages the A8 board should supply
• Garbage on the dot matrix at power-on
• Never hot-plug the A8 board or the display
• DMD controller LED stays on
• Bottom two rows of the DMD dark: row pins broken off the glass, bridged to the traces
• Nonsense message at boot, game stuck in a loop
• Display works in a Williams game but not in System 3

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