I have the same issue with my Spider IV 75 the part # 35-00-0335 has a TDA7293 I.C on it which below when I took it out of the box and plugged it in. When I plugged it in it produced a boom sound and within a second I turned it off and there was this burning smell after which I dismantled the amp head and was able to determine that the TDA7293 I.C was burnt to death. I then disconnected the PCB Data circuit which I knew is used for power amplifier and then tried turning on the unit and plugging in headphones and the effect modeller works perfect with the headphones output. Now I've replaced the I.C and still am getting the voltage run into the speaker which I assume is because of one or both of the 100V 47uf capacitor being burnt too. I need the PCB data code part if possible and I will pay for it, I know I've dismantled the amplifier so now the warranty has been voided and the warranty wouldn't even help me because if I was to send it back to Guitar Center for repairing/replacement is it is brand new, they would've told me that there is no warranty if the item is damaged through voltage fluctuation.