Egnater Tourmaster 4100 treble trouble

Hi,
I have a egnater Tourmaster 4100 Head with a problem. On the fourth channel the treble knob works like a Backwards volume knob, if you turn up the treble the amp gets quiet, if you turn it down amp gets louder. never heard of this problem. also there is no treble in that channel what so ever. this only happens with the fourth channel all the other ones sound perfect.
ANY HELP WOULD BE APPRECIATED

i have a sneaking suspicion that i would have to replace the potentiometer, but i dont know what potentiometer to use so help with that would be fantastic too if that is the problem.
Thanks in advanced

sounds like it's wired in wrong.
Problem with these is....good luck getting in there and working on those boards. theres 5 of them IIRC.

these amps were so prone to gremlins, and it's such a shame, cause they sound so fucking good.