Rockerverb 100 FX Loop not working

[TheLemur]

Hey all,

So, short and sweet - the FX Loop in my Rockerverb 100 seems to have stopped working. I thought it was my FX unit (Line6 M13), but I brought it in to work and tried it through another amp, and it's fine.

Basically, I'm using the 4 cable method so that I can have some FX pre and some post, but none of my post FX (going through the loop) ever come back.

Anyone ever have this problem? Could it be as simple as one of the tubes in the tube buffered FX loop going bad?

Thanks!