Based on your observations thus far, there's an open circuit (broken connection) somewhere between the +12V input and the empeg ground plane. The path for this is supposed to go through that fuse.

Once you have the board out the case, measure it again. It should be near zero ohms.

Also measure the resistance from the outside contact of the DC power jack and the fuse (either side). This should also be near zero ohms.

And one more: the black wire on the 4-wire cable nearby is also supposed to follow the same path -- it should measure zero ohms between it and the fuse, and between it and the outside contact of the DC power jack.

Cheers