If the sound is different between the "active" and "bypass" modes, then the switch is okay.
If I'm reading the problem correctly, the pedal switches from "bypass" to "active" but when active, sounds like it's rocked all the way back, no matter where the pedal is positioned, right?
If that's the case, either the pedal's rack and pinion are not turning the pot shaft, or the pot is dirty/worn out. Look at the mechanical bits first. If you open the back of the pedal, it's pretty obvious how they're supposed to work. The rack moves up and down, and makes the pinion gear turn around. The pinion is mounted directly on the pot shaft. There's a little plastic loop that's supposed to hold the rack engaged in the pinion. If the loop's come loose, the rack could slide up and down, but not turn the pot.
I see the Dimebag has a bunch of extras features, any one of those might cause the problem: pots and switches are always the first suspects. Try twiddling all those extra gadgets and see if they affect the problem.
