Sounds like a short on the main board. It could be most any part. IF you want to proceed further, pull the plug from the power supply and use an ohmmeter to check the resistance to ground on the main board connector. If there is a direct short, you would read about 1 ohm or less to ground on one of the power supply lines. You probably have a 3 volt line, a 5 volt line, a 12 volt line and/or maybe a 24 volt line. There is a possibility of a shorted diode or capacitor on one of these lines and that would be an easy fix. The alternatives are not so good.
If you want the unit fixed, go to
hxxp://www.pansatservice.com/policy.htm. I sent in a 3500 a few years ago, with a check, and they had it back to me, fixed, in less than 10 days.