After unplugging a burnt GI connector, the DMD stopped working. All voltages reach the display except the high voltage, which is also missing at the power supply output; even a replacement power supply gave no high voltage.

DMD dark after work in the backbox: transformer wire pulled out of its plug

Cause: One of the transformer wires feeding the power supply had pulled out of its connector housing, so the high-voltage section got no AC.

Checks

• Measure each voltage at the DMD and at the power supply outputs.
• Check the transformer plugs feeding the power supply pin by pin; look for a pin backed out of its housing.
• Check the fuses and their clips; these fuse holders crack and lose grip.

Fix

• Re-seat the wire, then re-pin that connector with new pins.

The DMD supply is high voltage (around 100 V on the display side) and the transformer leads carry line-derived AC; unplug the game and let the supply discharge before handling them.

Systems

• Data East CPU Version 3

Games

• Jurassic Park

Related tips

• DMD shows lines or garbage and no controlled lamps light
• Dot matrix shows lines or lights solid, and no CPU lamps work
• Adding jumper wires across DB1 and C4 (520-5047-00/-01/-02)
• Which DMD brands are hit by a blown lamp fuse
• Power supply gives no +5 V
• Burnt GI pin on the Data East power supply header: move it to a spare pin
• Burnt 12-pin power supply input plug stops the game booting
• Square power supply plug part numbers

Source: Pinball Repair help group!! (Facebook group)