After replacing a burnt J120 GI connector and header, the strings on J120 pin 8 and J121 pin 7 still don't light. Their fuses (F109, F110) are good and power reaches the fuses.

Two GI strings still dead after fixing a burnt J120: broken pads and traces

Cause: Removing the cooked header pins had damaged the front traces and through-holes between those pins and their fuses.

Checks

• Check continuity from each header pin to its fuse clip, and from the top of the board to the bottom at each through-hole.

Fix

• Run jumper wires on the back of the board from each affected header pin to its fuse clip, or stitch the through-holes.

Systems

• WPC DCS

Games

• Star Trek: The Next Generation

Related tips

• GI string dead after connector replacement: broken traces
• All backbox lights out with good fuses: burned J120 GI connector
• Continuity checks after replacing GI header pins
• A lamp row very bright or dead
• Lamp matrix faults with all lamp transistors good
• Cannons and a flipper lose power at once: a fuse that looked fine was blown
• General illumination strings
• No lamp matrix lamps light

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