Edited by JUSTINDTH - 11/27/14 at 8:47am
Re: The pot. You may be able to swap it out but you may not like what you see... It's probably a cheap/readily available alps blue velvet pot.
IIRC there are security bits holding the black panels to the wood casing so you may have to find the proper tool to open it.
Ruling out the obvious. Are you sure the headphone jack is plugged in all the way? Good battery?
Have you contacted Grado?