Crate GT 80 cutting out. Patch chord works

I have a Crate Gt 80 that is cutting out like many people have posted. I ran a patch chord from line in line out on back of amp and this works. Has anyone with this problem and patch chord solution figured out what is wrong. I have put a new input Jack and two Zener diodes that didn’t fix the problem. Running the patch chord work doesn’t cut out with patch chord. So many people have had similar problems with these amps the solder connection on the board look good no burn marks. Thanks