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  1. #151
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    Quote Originally Posted by omega99 View Post
    well it lasted a whil, but now got the RLOD again,
    I noticed caps C14 & C15 on the psu board have slightly domed at the top - any body know how to test the psu while unplugged from the m/board?
    I had a Duo back a few months ago where it had the red light issue.

    I changed the usual but no difference but like you I noticed those two caps on the Power board bulged so I changed them also and bingo, back in action.. I had another Duo that had died about 6 months previously and I’d given up on it but after this fix worked I tried it on that also and it was the issue there too

    Worth a try I guess, only cost a few cents for me...
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  2. #152
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    question i ask myself is it worth doing again as when blind as a bat i would need to send it out to a repair centre.
    is there much life left in these old slow boxes is repaired again?

  3. #153
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    Upgrade to much faster box for only 79 https://www.world-of-satellite.co.uk...er/formuler_f1
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  4. #154
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    If you are able to do the repair yourself its a cheap fix and worth doing (even just to keep the box as a spare). But yes the duo is a slow box compared to what is available cheaply now. Its always nice to have a good excuse to upgrade to something faster even though I like repairing equipment.
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  5. #155
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    Quote Originally Posted by mcquaim View Post
    I had a Duo back a few months ago where it had the red light issue.

    I changed the usual but no difference but like you I noticed those two caps on the Power board bulged so I changed them also and bingo, back in action.. I had another Duo that had died about 6 months previously and I’d given up on it but after this fix worked I tried it on that also and it was the issue there too

    Worth a try I guess, only cost a few cents for me...
    changed both the caps but sadly the red dot of death remains, they where cheaps caps when measure on the fluke meter 1540Mfd & 1550Mfd when they are supposed to be 1500Mfd

  6. #156
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    Quote Originally Posted by omega99 View Post
    changed both the caps but sadly the red dot of death remains, they where cheaps caps when measure on the fluke meter 1540Mfd & 1550Mfd when they are supposed to be 1500Mfd
    Nothing to do with being cheap capacitors. Even the highest quality electrolytic capacitors have a tolerance of +/-20% of their marked value so anything between 1200uF and 1800uF is within tolerance.

    Even the lowest quality electrolytic capacitor probably will have fixed the fault if the component you replaced had been the fault (assuming that the component was fitted correctly as electrolytic capacitors have a polarity)

    The difference between a high quality capacitor and a lower quality capacitor in these types of application is likely to be the life expectancy of the component.

    A capacitor life expectancy is rated in a number of hours at a certain temperature.
    Typically for a lower specified capacitor this may be 5000 hours at 85 degrees C where the life expectancy may double for every 10 degrees C below 85C that the capacitor is actually operated at. For a higher specified device the specification may be typically 5000 hours at 105 degrees C, again doubling for every 10C below 105C. In a power supply the capacitor may be positioned close to a heat sink in an ambient temperature of, say, 55C. In these conditions the lower specified capacitor may have a life expectancy of 15,000 hours whereas the higher specified capacitor this is 25,000 hours.

    Unfortunately it's not just as simple as this. capacitors have a ESR (Equivalent Series Resistance) and in a switched mode power supply the lower this value the better. Higher values of ESR cause more self heating in the capacitor and temperature affects the life. Furthermore as the capacitor degrades the ESR will increase causing greater self heating. A lower specified capacitor is likely to have a high ESR value[[1] whereas a higher specified capacitor, for a switched mode power supply, will have a very low value.

    [1] You may not actually find a ESR value on some data sheets for lower specified capacitors as they are not recommended for use in some locations in a switched mode power supply.

    Some manufactures capacitors such a Panasonic, Rubycon and a few other respected brands seem to perform to their published specification while capacitors from some (Korean) manufactures, such as Samyoung, with similar specifications seem to fail prematurely.

    So if replacing a capacitor in a switched mode supply ideally:
    i) Select one with 105C temperature rating
    ii) Select one which claims a low ESR or low Z. Avoid any capacitors where there is no data given on this parameter. Not all 105C components are low ESR/low Z
    iii) Ideally buy a reputable brand
    iv) Buy from a reputable source. In the UK this may be CPC, RS or Rapid Electronics - there may be many more reputable UK suppliers but like anything else there are fake branded capacitors in the marketplace or subtly worded misleading listings where the the no-name components is claimed to be equivalent to the branded item's part number

    The difference in price between a low and high specified capacitor may be of the order of 0.20 GBP . This difference may be significant for a manufacturer buying in 10,000s of components but insignificant for a DIY repair when buying very small quantities.
    Last edited by adm; 17-11-17 at 11:08.
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  7. #157
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    Quote Originally Posted by Alec View Post
    I have measured some voltages on the IC'sAttachment 28156Attachment 28157
    from H4R7's
    I = 1.9v supposed to be 2.59v
    F = 0.7v supposed to be 1.25v
    C = 1.2v supposed to be 1.25v

    would it be the cap or the H802 that would cause F to be at 0.7v

  8. #158
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    Quote Originally Posted by omega99 View Post
    from H4R7's
    I = 1.9v supposed to be 2.59v
    F = 0.7v supposed to be 1.25v
    C = 1.2v supposed to be 1.25v

    would it be the cap or the H802 that would cause F to be at 0.7v
    replaced c814 220uF with one I had lying about as I had nothing to lose at this stage & hey presto away she went again. Forgot to measure the voltages out of the 4R7's

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    I just had the red light issue again; opened it up and it's the same capacitor.
    I find that odd; there must be over voltage on it or something, all the other caps appear fine.
    Anyway, I replaced it again [had a couple of spares from last time], and the old VU duo is working again.
    After tightening the beam, we no longer get astra here in southern Portugal, so the box is of very limited use.
    I'm not going to replace it if it dies.

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