hi,
open the cover of the rf part. near the input connector search for a low value resistor (several ohms) or for a high value inductor (tens-hundreds uH). check with an ohm-meter to see if they are burned. if so, replace. if not, look outside the metallic case for a resistor (also near the input rf connector) which is connected to the first pins of the rf metalic block (lnb power supply pins). this resistor should also have low value. see if it is burned or not. if so, replace.