There's a power supply schematic courtesy of Burnham Beech here -
Echostar LT8700 Power Supply Circuit Diagram
I had a PS problem (or two) when I had my SR7800 (same PS) working hard back in the distant past. A couple of fast diodes take a lot of punishment; unfortunately I can't remember exactly which ones they were now. I'll dig it out later and see if I can spot them.
Other than that, check the usual suspects - the electrolytics.
Beware though, it's a pig to work on - big voltages flying all over the place
Llew