resistance value on vu duo2

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

  1. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    I don't understand any of this. Could you please write precisely? Do you know the parameters of the C820 because I do not know what to look for in the store? The meter shows about 230 uF. I know it's not a precise measurement but it showed 1.5 times more than you wrote before.


    Which regulator can be blocked by the EN pin? Each? How can I find it? Most regulators only show 12V at the moment.
    I think she's resigning. Too many unknowns here.
     
    Last edited: Jan 5, 2021
  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    C820 capacitor question..
    I need to know the location, or at least the area of where it's placed to measure it because there are allot of ceramic caps present on the board, and I couldn't find it therefore I also not known the size of it.

    If/when you have the 12v to the inputs of the dc/dc converters, but they all not giving an voltage output, then you may assume that they are not enabled/not active.

    Which dc/dc converter is responsible to enable them is as for this duo2 board yet unknown, i still need to figure this out.
     
    Piotrekop likes this.
  3. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    As for the Dc/Dc converters all inactive issue..
    It's still unfinished because I still need to added more info into it, but to help you faster I show you this..
    Although every Dc/Dc converter has been controlled due the U705/HCT32, but without the 5v input from the U810/GAF than it seems to me that they all will be disabled.
    And thus, check the U810, if it has the 12v input and 5v output.
    The output voltages may between the 4/5V.

    One note, all Dc to Dc converters having a zero ohm resistor between the EN pin and the U705 just as noticed on this drawing.
    But the U810 has a resistor value between the 12v input and the EN pin.
    Thus on the drawing it shows as a zero ohm resistor, but it's not, this will be changed in the final drawing.
     

    Attached Files:

    Piotrekop likes this.
  4. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    Thank you Johnny.
    The drawing was very helpful :):):)

    1. I understand that the U705 DC / DC converter gets the current first and controls the rest? Yes?

    As for this motherboard, it is probably damaged irretrievably. :(:eek:

    I replaced this board with a second one and the white LED is also lit after replacing the capacitors.
    All voltages are correct and also comply with this figure.

    The problem is only with the U 702 chip. The resistance is correct. No output current. There is only current on pin Vcc - 12.15V.

    2. Does it mean that the U702 chip is faulty?
    3. Which layout should I check? Or is it clearly a U702 system error?
    4. If the U702 is damaged, what symbols should I use to buy a new one in the store?
    5. Will that be it?

    Thanks, :)
     
    toysoft likes this.
  5. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    The U702 is only active when the box starts up and it is used for feeding the fan.
    Thus no, this one is not faulty.
    Please wait for my (hopefully) final drawing which shows all the voltages of most of the ic's which are most likely related to the voltages delivery's.

    Or, since you have the led status,
    I would try the jtag method before thinking of a hardware fault.
     
  6. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    @Johnny,
    Now I have a hardware problem ...
    During the measurements of the U824 and U823 system, I made a short circuit with the meter. A light bubble appeared near the card readers.
    The white led only lights up briefly and then goes out.
    No power:
    - on the L101 coil (it should be 1.2V)
    - F401 (should be 1.4V)
    - L803 (should be 1.0V)
    - C837 (should be 2.5V)
    - L802 (should be 3.3V)
    - L811 (should be 1.5V)
    - L801- is 1.92V (it should be 5.3V).
    Previously, all voltages were correct. The voltages on the other systems are normal or low.
    To use the jtag method, I would like to restore Duo2 to its previous state, i.e. to the effect of shining a white led.
    Do you have any idea where to look?
     
  7. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    I don't really understand why you continued measuring when I already mentioned that the jtag might be the best thing to do instead of thinking about a HW problem.

    Short circuit due to measurements.
    I have no idea how to react to this, creating short circuits with measurements can cause fatal defects.
    And then so much so that it flashes elsewhere doesn't make it any easier.

    I don't know how thick your measuring probe pen is, but a standard rule for measuring smd components is to use a needle probe, or if it has a thick pen, mount a thin needle on it for safe measurement.
    In any case, I cannot tell you what went wrong, that is something you will have to decide for yourself.
    My best idea is, maybe the ic is defect with which you made the short circuit.
     
  8. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    I was measuring the U824 chip, i.e. in the upper part of the board and the balloon was in the lower part of the board on the card reader side. I thought that the front panel was damaged. I checked the front panel and there is no defect. The U824 chip shows the correct voltage. Probably working fine. I don't know where to look for this defect. If you do this drawing with power supply, will you be able to find the damaged element in my case?
     
  9. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    First of all you must be aware that these motherboards has several print track layers.
    In the old days it were mainly one side, the print side, later came the tracks on the print side and parts side, but nowadays it has also inner layers, and this board has at least tracks on the print, and parts side and two inner layers as an sandwich board.

    Why do I tell this all, now because if you create a short circuit which shows elsewhere a flash and afterwards this area has because of that a balloon (the surface is bulged), and all voltages drops to lower.
    Then the risk of having a inner layer short circuit with the inner layers, or inner layer and one of the parts, or print side very high.

    Normally when that happens it is no longer repairable.
    Til now I can only imagine how it looks but assume it is of what I think it may be, then you could try to open the balloon, and to try to fix the short circuit in it, but the chance that you will find and can repair it, is very, very, very low.

    Maybe if you give a picture of it then I may become to another thought, but based on your description I come to this.
    In any case, sorry to say but based on it I get not the impression that it's a defective part, rather an print track short circuit.
     
    Piotrekop likes this.
  10. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    Pictures of the Duo2 board are attached. I didn't notice anything but maybe I don't know enough ...:)
     

    Attached Files:

  11. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    Okay first of all, you seems to have doing a nice job with the recapping, and that's at least some good news.
    As for the pictures, they do not indicate any dramatic PCB damage, as also no blown DC/ DC converters as I would had expect based on your story, as also no short circuit fire damage to the U824 pins.
    So I can not see any visual damage on this pictures you had taken, and that's at least some good news.

    In that case...
    What I would like to know, if you still can remember which pins you shorted from the U824.
    I would also like to see an overview of which voltage ic's do no longer supply the correct output voltage, shown on this news voltages overview.
    This is to get an idea of what might be wrong with the board.
     
    Piotrekop likes this.
  12. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    I don't really remember which pins in U824 shorted. They were definitely adjacent pins. The options are 3. I am so reminded that I could have shortened the wire pins from the card reader. During the measurement, I put my hand on these pins and a short circuit could occur. This is how I remember it now, and maybe that's why a speech bubble appeared near the card reader.

    But I will take these measurements additionally that you asked for.
     
    Last edited: Jan 11, 2021
    Johnny B. likes this.
  13. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    I did IC measurements. Unfortunately, I worsened the condition of the motherboard again. I rested my hand on the card reader pins again. I short-circuited again in the same place. I just don't know which pins on the reader shorted. The difference is that the CPU was warm before. He's cold now.
    I found two errors in the drawing. I marked with an exclamation "!"
    It is about:
    1. U810 or U818?
    2. U817 and pin sequence - 5V input or GND?
    3. resistor R854 or R845 at U810?
    Measurement attached. A bit of a poor .PDF quality
     

    Attached Files:

    Last edited: Jan 12, 2021
  14. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    Cpu not warm, may logic due all the voltages drops.
    As far as I see it, than you seems to have a issue with the 5v circuit.
    I do not think that it is the 5v delivery from the U803, but rather another part that uses the 5v.

    To see if it's a issue with the 5v circuit, or the 3.3v circuit I need to have some ohm measurements as.
    Ohm value between the ground and the circuit,
    5v = ohms
    3.3v = ohms
    2.5v = ohms
    1.3v = ohms

    It does not matter were you measure it, as long it is a measurement from the circuit it's fine.
     
  15. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    I don't know if I understood correctly. Do I measure all ICs or just one? Which IC are you most interested in?
     
    Last edited: Jan 13, 2021
  16. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    I think this may tell something when I see the Ohms value from it.
    The Dc/Dc converter output pins of..

    U809 (1v) pin 7 or 8 ohms value =
    U810 (1v) pin 6 ohms value =
    U818 (1v) pin 6 ohms value =
    U807 (2.5v) pin 6 ohms value =
    U804 (1.5v) pin 7 or 8 ohms value =
    U806 (3.3v) pin 7 or 8 ohms value =
    U803 (5v) pin 7 or 8 ohms value =
    And just in case,
    U204 pin 5 (OUT1) ohms value =
    U204 pin 6 (OUT2) ohms value =

    This is to see which voltage circuit is the closest to the short circuit value.
    The one which is close to, or just is shorted to ground is most likely the circuit which is responsible for the drop of the other voltages.

    Of course do the measurements while the motherboard is not powered it on, as also not has been powered short before the ohm measurements.
    Because the caps must be unloaded to get a good ohm values.
     
  17. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    You mistook U810 with U818. I think there is a bug. I marked this in the picture in the post above. The U810 has no 6 pins and is at the very bottom of the motherboard. The U818 has 6 pins and is in the center of the motherboard. I understand you mean U818? Yes?
     
  18. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    Yeah indeed, the U810 must be the U818.
     
  19. Piotrekop

    Piotrekop Member

    Messages:
    90
    Likes Received:
    16
    Trophy Points:
    8
    U809 (1v) pin 7 or 8 ohms value = GND !!! - 7-8 pin = 0.010kΩ
    U818 (1v) pin 6 ohms value = 0.458kΩ
    U807 (2.5v) pin 6 ohms value = 1.318kΩ; 7 pin = 0.005kΩ - GND !!!
    U804 (1.5v) pin 7 or 8 ohms value = 7-8pin = 2.07kΩ
    U806 (3.3v) pin 7 or 8 ohms value = 7-8pin = 0.005kΩ - GND !!!
    U803 (5v) pin 7 or 8 ohms value = 64KΩ
    And just in case,
    U204 pin 5 (OUT1) ohms value = xxxkΩ
    U204 pin 6 (OUT2) ohms value = xxxkΩ
     
  20. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

    Messages:
    2,412
    Likes Received:
    1,154
    Trophy Points:
    113
    Gender:
    Male
    Location:
    Netherlands
    Home Page:
    Yeah that is pretty messed up, and normally when more than one voltage circuit is shorted, then it's in most cases a cpu issue.

    But, based on the measurements,
    U809 (1v) pin
    U807 (2.5v) pin
    U804 (1.5v) pin
    U806 (3.3v) pin
    Are close to ground, therefore I would remove them to see if it's the short to ground fixes.

    It is not to say if it is one of them, or caused due a print track short circuit or shorted ceramic cap, or something else because as I say before, since there are more circuits involved, It is not certain if it cause do one dc/dc converter, normally caused due a parts that works with these voltages as the cpu.

    Therefore removing a Dc/Dc converter to see if the shortcut will be solved could be useless, but in this case there are no other options.
    You could also consider not to remove the ic, but the output coil to disable the ic from the circuit.
    As the,
    U809 (1v) pin, the coil L803
    U804 (1.5v) pin, the coil L811
    U806 (3.3v) pin, the coil L802

    After removing one of the coils, measure the output pin again to see if it gets a higher/normal value instead close to ground.
    These coils can be removed with a hot air station, but I do it mostly with two solder irons, or lift it a bit up with one solder
    iron, than the other side of the coil, etc.
    Using a hot air gun may damage the isolation of the coil wire.