resistance value on vu duo2

Discussion in 'VuPlus Duo2 Schematic drawings, Pcb images etc..' started by bjt01, Nov 13, 2020.

  1. Piotrekop

    Piotrekop Member

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    After removing the coils, do the IC measurement again as last?

    Do you have the parameters of such a coil somewhere?
     
    Last edited: Jan 13, 2021
  2. Piotrekop

    Piotrekop Member

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    I can't desolder these coils ... They don't react to temperature. Hot air soldering iron will not help here either. Too many items next to it.
     
  3. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yeah well, some skills are needed to remove ic's or coils, and I can't help you with it.
    I have my own equipment/tools to do it as two ksger T12 soldering stations which are be able to handle this kind of jobs.
    Maybe if you search on youtube to something as desoldering an inductor helps you.
     
  4. Piotrekop

    Piotrekop Member

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    After desoldering the L803, L811, L802 coils, do the same current measurement as before?
     
  5. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    When it's the pcb track side, then that sucks when that happens because then it may be some internal short circuits on the motherboard, or the cpu has died.

    If it's the ic side, then this is defective, and then you may have some luck.
    But I assume you measured the Pcb track side.
     
  6. Piotrekop

    Piotrekop Member

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    What to do after desoldering the coils? What to measure?
     
  7. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    It depends,
    When you have removed these coils, and you measure these short circuit values on the print track side, and not on these ic's output side, then you're done, it's no longer reparable.

    If you measure it on the output sides of the ic's while the inductor coils are removed, and the side (after the removed coil) of the pcb circuit not, then it could be another story.
    But I have the idea that you still have these wrong values on the pcb print tracks side.

    You could remove some other dc\dc ic's to see if it solves something, but I have my doubt that it will.

    For so far as I see it, then I can only give the advice to give it up.
     
  8. Piotrekop

    Piotrekop Member

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    I do not understand. I do not know what to do...
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    ............. What to do after desoldering the coils? What to measure? ...........

    As I said before, when the coil (inductor) is removed, measure the ohms value of both sides of the solder spots from where the coil (inductor) was soldered.
     
  10. Piotrekop

    Piotrekop Member

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    Is that the point? :)
    U809 (1v) pin, the coil L803 = top pin 4.48MΩ; bottom pin 0.010kΩ
    U804 (1.5v) pin, the coil L811 = top pin 26.2kΩ; bottom pin 2.24kΩ
    U806 (3.3v) pin, the coil L802 = top pin 21.8kΩ; bottom pin 0.006kΩ
     
    Last edited: Jan 15, 2021
  11. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Okay, what shows these measurement,
    That these Dc ic's are probably okay, and the short circuit is between the ground and the 1v as also the 3.3v circuits.

    Since the lowest value is the 3.3v side, I would use that first to try to find the part which may the reason of it.

    To be short,
    Measure all other ic's which are connected to these 3.3v circuit.
    The one with the 0.006kΩ or lower ohms value could be the defective one.


    And this will not be easy to find because it can be cause not only by a ic, but also (ceramic) caps and resistors who are between the ground and this 3.3v circuit.
    Even your new caps can cause it, since the reason why it happened were caused as you say creating a shorted circuit while measuring.

    Most worse scenario, is that it still could be caused due the cpu, or some shorted print tracks.
    And since there is no schematic of it, it makes it even harder to find.
     
  12. Piotrekop

    Piotrekop Member

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    Capacitors seem ok. I didn't measure resistors. Perhaps, possibly, suggest which resistors to check first after analyzing IC measurements. Are these all 3.3V ICs or have I missed something?

    U808 PIN 3 (3.3v) = 99.7kΩ; pin 8 = 1.015kΩ
    U821 output (3.3v) = 1.54kΩ
    U201 (3.2v) pin 3 = 4.51kΩ; pin 4 = 4.46kΩ; (3.3v) pin 5 = 27kΩ, pin 8 = 27kΩ
    U703 (3.2v) pin 3 = 6.34kΩ, pin 6 = 6.16kΩ, pin 4 = 1.527kΩ
    U820 (3.3v) output = 1.24kΩ
    U822 (3.3v) output = 1.55kΩ
    U702 (3.2) Ctrl = 36.6kΩ
    U826 (3.3v) output = 1.54kΩ
    U817 (3.3v) output = 1.523kΩ
    U819 (3.3v) pin 3 = 0.006kΩ - GND - !!! ???
    U403 (3.3v) pin 1 = 6.60MΩ, pin 2 = 6.47MΩ, pin 5 = 0.006kΩ ??? !!!, pin 4 = 8.77MΩ
    U809 (1.0v) output pin 7-8 = 4.45kΩ

    U818 (4.9v) pin 1 = 0.20kΩ ???; (5.0v) input pin 3 = 0.005kΩ ???
    U807 (4.9v) pin 1 = 0.20kΩ ???; (5.0v) input pin 3 = 0.005kΩ ???
    U103 (4.9v) pin 6 = 0.21kΩ ???
    U806 (3.3v) pin 7-8 = 19.0kΩ
    U408 (3.3v) pin 3 = 4.44kΩ, pin 4 = 4.38kΩ, (3.2v) pin 5 = 1.012kΩ, (3.2v) pin 8 = 1.010kΩ
    U204 (3.3v) pin 3 = 3.95kΩ, pin 8 = 27kΩ
    U816 (4.9v) pin 5 = 0.21kΩ
     
    Last edited: Jan 16, 2021
  13. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Given the ohm values, not everything relates to this 3.3v circuit.
    What strikes me is the 5v, which has a lower value and thus appears to be closer to the short circuit source.
    If I can find the time for it, then I will tomorrow check what the effect is if I put a short between the 5v to the ground, to see if the others ohm values also go down.
    This could maybe help to analyze it, because right now I have no idea what to think about all of this.
     
  14. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    U819 (3.3v) pin 3 = 0.006kΩ - GND - !!! ???....... No it should be something as 4.37M

    U403 (3.3v) pin 1 = 6.60MΩ, pin 2 = 6.47MΩ, pin 5 = 0.006kΩ ??? !!!, pin 4 = 8.77MΩ
    U818 (4.9v) pin 1 = 0.20kΩ ???; (5.0v) input pin 3 = 0.005kΩ ???
    U807 (4.9v) pin 1 = 0.20kΩ ???; (5.0v) input pin 3 = 0.005kΩ ???

    By shorting the U806/L802 to ground, the,
    U403 (3.3v) pin 5
    U818-U807 input pin 3 are indeed dropping to a ground value.
    But as for the U819, pin 3 has no issue with that, only the pin 1 of it.

    As for the U818/U807 (4.9v) pin 1 = 0.20kΩ ???, these do not react when there is a short to the 3.3v circuit.

    By knowing this, then there is a issue with the 3.3v circuit.
    And because you seems to have also a issue with the U818-U807 0.20kΩ pins, and these do not react , when I create a short circuit, and thus has these ic's two issues instead of one, then it could be a issue with the U818 or U807.

    But still, it is never to say that it will be caused due one of them, a short circuit is always tricky to solve, therefore if you decide to remove them, you do it on your own decision.
    My advice, measure first the surrounding caps/resistors before to decide to remove it.
    And be aware that it still can be another part as the U819 due the pin 3 issue.

    As for the U818-U807 5v input was by seeing this incorrect, these has the 3.3v input and is updated on the drawing.
     
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  15. Piotrekop

    Piotrekop Member

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    I measured capacitors and resistors around U818, U807, U809.
    Measurement of suspicious capacitors and resistors:
    C8233 - 0.006kΩ - GND
    C8(3 or 5)4 - 0.006kΩ - GND
    C302 - 0.006kΩ - GND

    R878 (0.00kΩ) - 0.020kΩ - GND, 0.021kΩ - GND
    R877 (0.00kΩ) - 0.021kΩ - GND, 0.021kΩ - GND
    R311 (10kΩ) - 0.006kΩ - GND
    R312 (10kΩ) - 0.006kΩ - GND

    C843 - 0.010kΩ - GND
    C842 - 0.010kΩ - GND
    C841 - 0.010kΩ - GND
    C845 (28.8kΩ) - 0.010kΩ - GND
    C848 (28.8kΩ) - 0.010kΩ - GND
    C8232 (4.39kΩ) - 0.010kΩ - GND
    C818 (4.39kΩ) - 0.009kΩ - GND

    Does anything come of it?
     
    Last edited: Jan 20, 2021
  16. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    The measurements are done nicely and the parts which are the closest to the ground are suspicious, but still the only way to know if it's caused due a part of which you think it could be the one, is to remove it.

    As for the measurements which are higher than the 0.006kΩ value in this case, can be excluded from the problem.
     
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  17. Piotrekop

    Piotrekop Member

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    Which chip do you think should be desoldered first? U818-U807-U819? After desoldering which points on the motherboard should be measured?
     
  18. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    After removing you must measure the 3.3v circuit, when the ohm value rises after the removal, then you have found the defective part.
    I would try first the U818 and/or U807 to see if it makes some difference.

    Nevertheless, which one to remove is always a gamble because as I already said earlier, every parts which has some contact between a ground or has a ground pin, and in this case this 3.3v circuit could cause it.
     
  19. Piotrekop

    Piotrekop Member

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    I desoldered U818. It cannot be done without damaging the plate. It is a very difficult chip to desolder because it has an additional contact to the mass on the belly. 8 pins + bottom soldering to GND.

    Here is the measurement of the 3.3V circuit.
    Measurement before and after desoldering U818.

    U807 (4.9v) pin 1 = 0.20kΩ ???; (3.3v) input pin 3 = 0.005kΩ ??? => (4.9v) pin 1 = 0.030kΩ , (3.3v) input pin 3 = 2.88kΩ ↑
    U819 (3,3v) pin 3 = 0,006kΩ - GND - !!! ??? => (3,3v) pin 3 = 2.86kΩ ↑
    U403 (3,3 V) pin 1 = 6,60 MΩ, pin 2 = 6,47 MΩ, pin 5 = 0,006 kΩ ??? !!! , pin 4 = 8,77MΩ => (3,3 V) pin 1 = 6,60 MΩ, pin 2 = 6,47 MΩ, pin 5 = 2.89kΩ ↑, pin 4 = 8,77MΩ

    I measured capacitors and resistors around U818, U807, U809.
    Measurement of suspicious capacitors and resistors:
    Measurement before and after desoldering U818.

    C8233 - 0.006kΩ - GND => 2.88kΩ
    C8(3 or 5)4 - 0.006kΩ - GND => 2.88kΩ
    C302 - 0.006kΩ - GND => 2.86kΩ

    R878 (0.00kΩ) - 0.020kΩ - GND, 0.021kΩ - GND => 0.029kΩ ↑, 0.029kΩ ↑
    R877 (0.00kΩ) - 0.021kΩ - GND, 0.021kΩ - GND => 0.029kΩ ↑, 0.029kΩ ↑
    R311 (10kΩ) - 0.006kΩ - GND => 2.87kΩ ↑, 12.84kΩ ↑
    R312 (10kΩ) - 0.006kΩ - GND => 2.87kΩ ↑, 12.92kΩ ↑

    C843 - 0.010kΩ - GND => 0.010kΩ ???
    C842 - 0.010kΩ - GND => 0.010kΩ ???
    C841 - 0.010kΩ - GND => 0.010kΩ ???
    C845 (28.8kΩ) - 0.010kΩ - GND => 0.010kΩ ???
    C848 (28.8kΩ) - 0.010kΩ - GND => 0.000kΩ ↓
    C8232 (4.39kΩ) - 0.010kΩ - GND => 0.010kΩ ???
    C818 (4.39kΩ) - 0.009kΩ - GND => 0.009kΩ ???

    The value of the capacitors is correct => 0.010kΩ ???
    Do you see any error besides the U818 chip?

    U818 to be replaced with a new one?
    Desolder U807?
     
  20. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Before value,
    U807 input pin 3 = 0.005kΩ
    After the removal of U818
    U807 input pin 3 = 2.86kΩ ↑

    Based on this information tells me that you have found the defective part, the U818 needs to be replaced for a new one.

    Q: I desoldered U818. It cannot be done without damaging the plate..
    A: These can just be removed/re-soldered with a hot air gun, and by picking it up with a tweezer.

    And, I mostly use kapton tape to protect the surrounding area for heat.
     
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