Hi, I recently bought a used Fender Rumble 100 Amp from eBay. Most of the time it's working fine, however, on three occasions, the speaker went silent. At least on two of these three occasions this happened when I was playing on rather high volume and also using effect pedals. When turning the amp off an on again the power indicator light is blinking, the speaker is still silent. After a few minutes the amp works fine again. Does anybody know how I can fix this? Cheers!