Doesn't boot

Discussion in 'VuPlus Duo2 Hardware troubles and Repair support' started by amila4341, Feb 15, 2021.

  1. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yes that is, because they are soldered to/between the same circuits.
    Only when you measure the smd caps itself while it is removed, and it measured as if it shorted, than can you assume that this smd cap is defective.
    However if that is, than it's to my idea impossible that the box starts up with a shorted cap of the 1v circuit.

    Therefore I had not the impression that you had a issue with this 1v circuit, and more the idea of a bad cap, or related to heat.
     
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  2. amila4341

    amila4341 New Member

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    Yes when caps removed and check them, caps are allright. I still can't understand if caps solder pads is shorted what is the purpose of it.it won't block ďc voltage
    Please let me know
    Thank you
     
    Last edited: May 18, 2021
  3. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    It depend if your measurement device is accurate enough to measure/show low ohm values.
    An short is 000 ohm, and my brand new working board gives 08.3 ohm which is close to, but not shorted.
    Why it is can only be tell if there was a schematic from it.
    What I can do tomorrow is to measure it again wit several measurements devices to see/check if it's accurate.
     
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  4. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    U809 ohm value between pin 1 ground and pin 8 voltage out is as on the measurements drawing, 08.3 ohm
    it starts with around 23 ohm and load to eventually 8 ohms but lets say 10 ohms or something close to it.

    ohmSnap1.jpg

    If you still measure it lower than this, than you may assume that you have a short circuit with it.
    But it will difficult to find or even may impossible because on the print side it is not to see were it goes as you can see on this picture, and by seeing this you may assume that the tracks to/from it are inner layers, so therefore not to follow.

    pcbSnap1.jpg

    But by other receivers with these low voltage, it is mainly related to the cpu, and may also be related with the memory.
    In any case, hoping for you it has no shorting, otherwise it may not repairable.

    What I would do is repair this dc to dc section, replace the removed parts, or put them back if possible and hope for an unexpected miracle.
    Other option is to feed the output with an external 1v Dc source, or a 12v to 1v dc to dc module, but that may maybe not without risk.
     
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  5. amila4341

    amila4341 New Member

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    Thank you
    R820.r817 ohm values please and
    To where 6th pin of u809 connected.is ir r817 ?
    Thank you
     
  6. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    6th pin of u809 is indeed connected to the resistor r817
    As for the r817, that's a zero ohms resistor as you can see on this voltages overview, but r820 resistor values I need to measure it, tomorrow.
     
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  7. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Just as I already thought due the output table of the voltage output resistor values setting , in this case to 1v which is to see in the datasheet, is the r820 resistor values 5k
     
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  8. amila4341

    amila4341 New Member

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    Misplaced c840 what is the value and size please
    Sorry to trouble you
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    c840 = 22uF
    size, since it must fit between two legs the 0402
     
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  10. amila4341

    amila4341 New Member

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    20210525_063906_01.jpg Screenshot_20210525-064440_Drive.jpg According to schematic r1 1nd r2 connected to pin number 4
    Is r1 and r2 is R820.r817 ?
    In the circuit R820.r817 connected to pin number 5 and 6 respectively.
    I want to know values oft
    R820.r817 please?
     
  11. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    The datasheet example is not always the same as on a motherboard, as you can see on the recommend coil value 4.7uH and the motherboard 1.5uH.

    Com pin 5, and En pin 6 are not connected to each other as also not the same as on the motherboard.
    There are some basic rules howto connect it as the resistor value for the 1v output, but as for the rest there is some space for the designer to design the dc/dc circuit.

    Also keep in mind that in this case the dc/dc ic is switched on/off by the En pin, but by other receivers this is not always the case.
    As also there are several types of ic's, at least two, this has SO-8.
    The one this is, is with one output pad (LX) and therefore are pin 7/8 Lx NC Not Connected in the chip.

    >I want to know values oft
    >R820.r817 please?

    Not sure why you asks this resistors again while it already were given.
    r817 0 ohm
    r820 5k