I have the same thing on a spider IV 75, it seem there is a general reliability issue with this amp. I precise that the screen and preset selection works properly during the breakdown, as well as the volume rotactor. I suspect the motherboard. the temperature on the surface of the DSP and other components look correct, less than 30 °C. I have also a regulator 7906CT delivering -5.9 instead of -6,8V indicated on the board to check. this is strange when the amp has been switched off a long time , the amp can work 5 min, before cutting off the sound. (no sound on the headphones output as well then). when the amp is turn on again just after that, it cuts off the souns some seconds after. it seems it needs some time to recover .. :-) that could make me thinking about a capacitor issue ? I also suspect a quartz to be half broken, I will still investigate and let you know if I can find any solution