I bought this Mesa Big Block 750 used. The power will come on and stay on but I get no sound. Also, the power to the footswitch is out as well. Sometimes I can turn it on and it will work fine for a few seconds (even the footswitch will work), but then the sound will start to fade and completely cuts out after a few seconds. I don't have a Mesa service center anywhere close. Does anyone know about a problem like this? Your help would be greatly appreciated!!! Barry