Missing dots, missing blocks of 32 columns, no display, unreadable or repeating garbage.

Dot matrix display faults

Cause: Missing dots: a broken or badly soldered pin on the glass. Missing 32-column blocks: a column driver chip on the display. No display: the display or missing voltages from the controller. Garbage: controller RAM. Repeating wrong pattern: a latch feeding the controller RAM.

Checks

• Measure the high voltages and fuses on the controller.
• Swap the display or controller to isolate.

Fix

• Repair the display pins or drivers, or the controller RAM or latches.

The dot matrix supply makes over 100 volts DC (+62, -113 and -125 V); keep fingers off the display and controller board while powered.

Systems

• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)

Related tips

• Dot matrix display blank or faulty
• One or two display columns stuck on
• Dot matrix display supply voltages
• Blank display, garbage or diagonal lines: reseat ribbon cables
• Dot matrix display power connector pinout and voltages
• Resets caused by a failing dot matrix display
• What the WPC dot matrix controller does
• Rebuilding the dot matrix high voltage section

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part One, Clay Harrell (pinrepair.com)