OP

Quoted from PghPinballRescue:

If you've got a JJP GNR, and part of the Hot Rail stops lighting, it is not necessary to remove either rail to make the repair.
Simply lift and slide the playfield out and set the rubber bumpers of the playfield support onto the lockdown bar.
Lift the back of the playfield, and lay it on a a 2X4 or something similar stretched across the cabinet (cushioned of course to avoid scratching the side rails).
This will get the playfield lifted up high enough to access the back edge.
Unplug the broken LED strip from the underside (located under the playfield on the left side). The 3 wires are red white and green.
Remove the 4 small phillips screws and 2 1/4" screws that hold the playfield guide in place.
Carefully slide the LED strip out the back of the machine. It is flexible, but try to avoid bending it as much as possible.
Find the broken solder joint and repair it.
Test it by plugging it back in before reassembling it.
Give the joint a little stress by bending it just a bit or by pressing on it with your finger to make sure you got a good solder joint.
Reassemble.