I was given a Carvin SX-200 head for free awhile ago by a friend. Apparently it had 'blown up' while he was using it and wouldn't turn on anymore.

Fast forward to two weeks ago. I take the amp apart and diagnose the problem; the VIPer100A (high speed switcher) and K817P opto coupler isolator were damaged, as well as a few capacitors and a resistor. I drove to the Carvin factory near my house and picked up the parts I needed and brought them home and installed them. Now the amplifier turns on but once it powers up, the Power LED indicator flashes on and off and the signal cuts in and out as if the amp is turning itself on and off. I can also hear the small board-mount transformer kick on and off as well. As far as I can tell I get a full signal and everything works, but the amp is automatically turning itself on and off! The on/off cycle is fast too, turning the amp on and off about twice per second. I dont see any other damaged parts on the circuit board and have triple checked all my connections. I installed sockets and plugged the new parts in to avoid possible damage during soldering.

Here is the SX-200 schematic. http://www.carvinmuseum.com/pdf/amps/sxpowerac.pdf
The parts I replaced are the 'Viper' (VIPer100A), OP2 (K817P opto coupler isolator), C31, C40, C41 and R40.

Any help would be very much appreciated. I am really close to bringing this poor amp back to life...