First, verify the oscilador circuit of the power.It´s normal the IC is damage or the mosfet.
Second, desconect the principal board and verify if has tensions on secundary part.If positive,the problem is on principal board.
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I do not have an schematic for this receiver. This receiver might not use LM317 or TIP42C but a different voltage regulator, try to locate where the 20 volts line from the power supply and follow it to anywhere near the LNB tuner circuitry. This type of IC is normally mounted on a heatsink.
Lastly if you are a subscriber, give you satellite service porvider a call to get a replacement.
You could check the voltages yourself to see if they are low. The horizontal polarity needs about 19 volts and the vertical polarity about 14 volts to work properly. If those voltages are lower by 25%, the receiver might failed to scan and that is when it locks up because is trying to find signal. The other issue could be a defective power supply if the receiver does not work after that 4 hours. There could be some capacitors that lost their dielectric strength causing the drop in voltage.
Let me know if you need further assistance.
Check inside the receiver for a defective LM317 IC or a TIP42C transistor, but before that you should check for proper voltage from the power supply to that IC.
LM317/TIP42C control the switching of voltages that power up the LNB, you should be getting 14 volts for vertical channels and 18 volts for horizontal.