DM800HD 5v circuit information

Discussion in 'DM800HD Schematic drawings, Pcb images etc..' started by Johnny B., Jul 5, 2015.

  1. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    If you have a problem with the 5v circuit, let say a to low ohm value.
    Than it can be one of the components on this circuit, mostly its the U24.

    More info, see the drawing.
     

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  2. cre4456

    cre4456 New Member

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    Hello. dm800 hd. 5 volts shorted. f1-f2 insurance open .fus resistance came .5 volts open circuit. After the short circuit resistance continues. Where short-circuited?
     
  3. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Hi,

    Removing the F1/F2 fuses does not isolate everything from the 5v circuit.
    The 5v source is the U6 LT1940efe which delivers the 5v and 3.3v.
    By removing the 0 ohm resistor R109 you disable the 5v from the circuit.
    After removing it you need to measure from which side the short accursed.
    If it is from the U6 side, then it is most likely a issue with the u6, if not then it could be every part that use the 5v.

    More about the U6, see this topic, u6-lt1940efe-issues.
    If you have another type motherboard which doesn't have this u6 12 to 3.3v/5v chip, then I need a picture of your motherboard, the print side.
     
  4. cre4456

    cre4456 New Member

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    I read u6 output of 5 volts. R109 hungry when I measure 5 volts. I separate circuits fed with 5 volts. short circuit continues. Short circuit is faulty CPU? the processor is warming up. I will take pictures as soon as possible. Thank your interest
     
  5. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    As far as I known does the cpu not use the 5v, but the 1.2v/2.6v/3.3v which are feed from the 12v (U6-3,3v/U7-2.6v) and 5v (U24-1.2v).
    As this image shows..

    dm800-p5-123-spots.jpg

    If you are sure that you only have a issue with the 5v circuit, than it may be the U24, the 5v input.
    To know that, you need to remove the R296 smd resistor or the U24 itself.
    Not really a easy task to preform, but is necessarily to know if it's caused due the U24.
    But be aware that if you disable the 1.2v to the cpu, then it's not wise to power on the motherboard.
    Better it to measure it by ohms.

    Also a note, be sure that you have the 2.6v, lower than for example 2.3v may mean that you have a issue with the U7.