Every backbox light is out although all the fuses test good.

All backbox lights out with good fuses: burned J120 GI connector

Cause: The J120 general illumination connector on the power driver board has overheated and burned, so the circuit is open at the connector.

Checks

• With the game unplugged, inspect J120 and the matching header for browned or melted plastic and darkened pins.
• Look at the board under the header for scorched or lifted traces.
• If the plug won't pull off, the housing pins may have fused to the header pins; don't force it.

Fix

• Replace both the header on the board and the connector on the wires; a new plug on an old header will burn again.
• If the plug is stuck, clip the wires close to it, remove and replace the header, then crimp new crimp-style (trifurcon) pins onto the wires rather than reusing an IDC connector.
• Repair any burned traces, and consider LED backbox bulbs to cut the current through this connector.

The GI circuit runs from transformer AC; unplug the game before working on the connector.

Systems

• WPC DCS

Games

• Popeye Saves the Earth

Related tips

• Two GI strings still dead after fixing a burnt J120: broken pads and traces
• No lamp matrix lamps light
• Lamp matrix fuse F114 (F106 on WPC-95) keeps blowing
• A lamp row very bright or dead
• GI fuse keeps blowing: isolate driver board or wiring
• None of the controlled lamps work, or they light in the wrong pattern
• Lamps light twice in the all-lamps sweep, or two lamps act as one
• GI string dead after connector replacement: broken traces

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