It could be that the switch on the master panel is dirty, not too difficult to fix but a little tricky and it can take patience. First take the switch out then take the swtich apartt by gently prying the rocker out of the case, this might be the second step, coming after removal of the outter case, I haven't done this procedure in a while. With the rocker out; clean the metal piece bent in a V with steel wool until clean. The trick is getting the V metal piece back in on top of the metal ball it rotates on and then getting the rocker on without the ball or v piece moving apart. I used a little dab of petoleum jelly to hold the ball inplace and keep the V still. If you attemp it good luck and if its $30 or so for a new switch you might as well try.
Duff