Okay. To repair it, you will need to add a new wire,
between the underside post of the power jack to the black capacitor,
as shown by the blue wire I have added to your photo below.



You can add this wire either on top of the PCB, as shown, or by routing the bottom end of it from the pin of the power jack from the underside of the PCB. This is the ground (or NEG pin of the power jack.

EDIT: The extra blue circle on the photo shows which pin of the EMI suppression block we are actually routing the new wire to. If you add the wire to the underside of the board, then you can probably run it from the DC jack to this exact pin, rather than to the capacitor on the topside. Might be tider that way. You cannot run the wire to the blue circle on the topside of the board, though -- don't even try it!

This fix replicates what you previously discovered by shorting the NEG contact to the empeg case, except it does it safely, and routes it through the original circuit path for EMI suppression.

Cheers