Lost my C-band signal KU is fine

[rocksahead]

I am using a 10' dish with your basic Chaparal feedhorn and 4DTV 920. Today my c-band signal went away. Poof. I thought it might be the lnb, so I swapped it out for a spare and still no signal. What is the next thing to check? Would the polorator or feedhorn probe be a suspect?

Thanks,

Rocks

 

[Lynskyn]

Try using the coax from the KU side to eliminate a cable issue.

 

[rocksahead]

Totally puzzled


I am resurrecting this thread because I finally got time to do more troubleshooting. I checked my cabling and it was fine.

However, and here is where it gets wierd, when I swapped cables the KU stopped working and the C-band started working fine. Then when I reversed the cables the KU still did not work, but the C-band did.

Currently my C-band works with either cable, as long as the KU lnb is not connected. When I connect the KU lnb, the C-band goes away; the KU never works, no matter what cable I use.

So, is my KU lnb fried, or is my 920 flaky? BTW the tdt count on my 920 is 1728.

If anyone has any suggestions, please offer them. College basketball is here; I really want my KU to work

Rocks

 

[PSB]

Sounds like a possible short in the Ku LNB!

 

[rocksahead]

More puzzled than ever

PSB,

I swapped out the KU lnb with a known good one.

Let me sum up:

When I connect the KU lnb with the C lnb aready attached the 4DTV responds by not gving me a C signal or a KU signal.

When I remove the C lnb and just connected the KU lnb; voila', the KU signal is fine.

If I add back the the C lnb without disconnecting the KU lnb the KU continues to give me a signal with no signal from the C lnb. Removing both cables and rec-connecting the C lnb the C signal fine; when I add the KU lnb I am back where I started.

BTW, polarity selection works fine when the lnbs are working independent of each other, so I am not really sure if the shorting is taking place in the polarator.

Can anybody shed some insight on what to try next ?

Thanks,

Rocky

 

[somery]

i don't know much about 4dtv here, just shooting out some ideas. What does the other end of these lnb coax cables connect to, is it an input selector switch or splitter/combiner or something? Do these go bad?

 

[rocksahead]

I have the lnbs directly into the 4DTV for troubleshooting; normally I have a DVB card slaved through a splitter. The behavior is the same through the splitter or direct to the 4DTV.

Thanks,

Rocky

 

[GrumpyGuy]

This is a weird one indeed. If I understand correctly it basically comes down to your being unable to power up both LNBs simultaneously, which may suggest a power supply or loading issue. Maybe the power supply in your receiver is degraded (e.g. partially blown diode bridge), or one of the LNBs is drawing excessive current(probably the C, as you have already swapped out the Ku)

Assuming you do not have access to an oscilloscope, I suggest measuring the LNB supply voltage from the receiver. First with no LNBs connected, then with only one LNB, then with only the other LNB, then with both LNBs.

 

[rocksahead]

It is simple enough for me to swap out the C lnb; so that will be my next move. I appreciate the feedback.

Thanks,

Rocky

 

[rocksahead]

Swapped out the C lnb with the same results. Next I'll check the voltage.

Kind of wish I had a second 4DTV, maybe a 922; fleabay here I come.

Rocky

 

[Hermitman]

You didn't mention if your cables were buried or not so I'll throw this out for info purposes. If a buried cable has a small split or gets a crack, it can give you wierd signal and LNB power indications. Sometimes the problems will only occur or change when the soil gets wetter or drier. If the water has gotten into the coax and soaked into the middle conductor area, the LNB may drop out at times and eventually completely. Corrosion occurring in the grounding braid can also cause problems. Normally you can check this by disconnecting both ends of the cable and using an ohmmeter to look for any current leakage. You'd also check the cable ground for any continuity with the soil for a jacket leak. Good luck and have fun.

 

[GrumpyGuy]

Take both DC and AC measurements. I'm not sure exactly how low the AC (ripple) reading on a healthy 920 should be, probably millivolts.

Maybe one of the guys has some idea of how smooth the DC powering an LNB needs to be.