Burned out LNB ?

Check the DC supply voltage/current.  If the LNB is open circuit or short circuit it is dead.  If it takes the approx milliamps as per the manufacturers info then then there is hope it may be OK.   Make sure the centre pin of the F type sticks out 2mm otherwise it may not make good contact inside the LNB.  The diameter of the centre pin is undefined and if a thick pin has been used before, a thin pin now may not make good contact - the spring effect inside the LNB F type socket may be poor.

Connect up a simple, inexpensive, power meter.   Test by pointing the LNB at a clear sky - away from satellites.  The power output should correspond to the noise from the front end amplifier only (say 100K).    Now point the LNB at your warm hand or ground soil/grass (say 300K).   If the noise level increases (400K) this is a strong indication that the LNB is good.

Comparison tests with a known good LNB and indoor receiver with Eb/No readounts will be conclusive, but obviously such a spare LNB needs to be available.

LNBs are very reliable in my experience.  It is the F connectors and the cable (moisture, corrosion) that are most often the problem.

LNBs can be burned out by excessive DC supply volts, differential earth voltages, lightning strikes and also by connecting to an OMT without a transmit reject filter.

Best regards. Eric.