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Thread: bad LNB?

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    Default Bad LNB?

    Hello all, am a new feller here and am needing/wanting some advice.

    I have had the austech DSD 4121 box for about 5-6 years and no problems. About 2 months ago picture started to flicker to a black screen for a few seconds upto maybe 15 seconds then back to picture, it only happened in the morning and came good once the day warmed up. I thought maybe some interference of some kind. It has gotten progressively worse so up onto the roof and I noticed the LNB cover has turned brittle as hell, I touched it and it fell apart. I covered the LNB with a plastic cup to keep the dew out and it sort of worked. I'm replacing LNB tomorrow, my question I have is, the loss of picture occurs only in the morning until it warms up and then starts again in the arvo as it cools down, rest of the day it doesn't flicker at all, does the weather affect a faulty/failing, I'm assuming the old one is faulty/failing LNB?. When I checked the decoder signal strengths I get high 70 to mid 90 signal quality and a constant low 90's to high 90's signal level if those numbers are of any help, it has started to pixalate in the AM and at times goes to a blue screen, box seems to boot, scan and load bouquets with no problems. If the new LNB doesn't fix this what else should I be looking at?. I'm a plug and play kinda guy and not much chop at these sort of things, I didn't know what an LNB was until a couple of weeks ago.

    Any responses would be most welcome.
    Cheers



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    Default

    I think you mean Altech UEC (Austech never made them)

    Anyhow... if the LNB cap has deteriorated, then replace the LNB as it likely has moisture and/or dirt/spiders/insects in it.

    Even if it's not the original cause of the problem, it will develop into one, so replace it regardless.

    The temperature-related issue is possibly dry solder joints or faulty components, either in the LNB and/or the decoder.

    The decoders are well known to develop such issues and replacement of some capacitors is the usual fix

    explains the fix in detail, but if you are not skilled with a soldering iron and surface mount components, best leave it to someone who is.

    Try replacing the LNB first.

    You will need to adjust the new LNB skew (rotation in the holder) to maximise the signal quality.

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    The way you describe it definitely sounds like moisture in the LNB -- specifically condensation forming when the ambient temperature goes down (morning and late afternoon) but re-evaporating once it heats up midday. Placing the cup on it kept new moisture out, but what was already inside was already inside, hence not complete improvement.

    I second mtv's advice -- best to replace the LNB.

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    your lnb has either a diaelectric resonate oscillator or a phase lock loop as its source of the local oscillator
    these drift over time and become temp sensitive also baronically sensitive so changes in weather can change the lo
    this puts it outside the tuned frequency hence loss of signal bin job for it
    unless you have 20ghz spec analyser and a sig gen as well the you would be very lucky to get it to work with out changing every component so I agree with mtv as well
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    Thanks to all who replied. Replaced LNB yesterday and made a great improvement but picture still drops out now and then. Am starting to wonder if it may be a line of sight issue, I live in a tree area, but I will first check out the Decoder box. Again much thanks to all who replied and assisted me.
    Cheers.

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    Quote Originally Posted by mtv View Post
    I think you mean Altech UEC (Austech never made them)

    Anyhow... if the LNB cap has deteriorated, then replace the LNB as it likely has moisture and/or dirt/spiders/insects in it.

    Even if it's not the original cause of the problem, it will develop into one, so replace it regardless.

    The temperature-related issue is possibly dry solder joints or faulty components, either in the LNB and/or the decoder.

    The decoders are well known to develop such issues and replacement of some capacitors is the usual fix

    explains the fix in detail, but if you are not skilled with a soldering iron and surface mount components, best leave it to someone who is.

    Try replacing the LNB first.

    You will need to adjust the new LNB skew (rotation in the holder) to maximise the signal quality.
    Yup, I did mean Altech, my brain doesn't work well when I think of 2 things at same time.

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    Quote Originally Posted by Strollin View Post
    Thanks to all who replied. Replaced LNB yesterday and made a great improvement but picture still drops out now and then. Am starting to wonder if it may be a line of sight issue, I live in a tree area, but I will first check out the Decoder box. Again much thanks to all who replied and assisted me.
    Cheers.
    Probably needs some more fine-adjusting of the skew, probably a good idea to use a spec or get an installer with a spec to assist. Yes, the trees would be an issue too, even if not now, the branches keep growing so it will eventually. Best to have the dish in nice open line-of-sight, or do some serious trimming.
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    do you get dropouts only when windy?

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