DM800HD U23-U24-U25 1.2v supply replacement.

Discussion in 'DM800HD Schematic drawings, Pcb images etc..' started by Johnny B., Oct 14, 2016.

  1. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    These U23-U24-U25 DC to DC circuit is quite complicated and difficult to solve if there is a problem with this circuit.
    Similarly, the parts are difficult to obtain, and often too expensive.
    That's why I'm working with this solution, the use of a DC to DC pcb.
    Of these are many species for sale on ebay.

    First thing to be done is to remove all the components that are related to the supply of 1.2v.
    As for the 3 caps, I have removed two of them, just to see what happens and I also have removed the coil L42 on the parts side.

    Dm800hd u24-25-26 parts removed.jpg

    Then follows the connection of the new system.
    As input voltage I first tried the 12v but as a whole needs to go to the 1.2v, this is a bit exaggerated, so I chose the 5v as input voltage.
    The total amps consumption is low, so the 5v circuit could handle it.

    The adjustment must be done before it is connected to the 1.2v circuit.
    Best is to have a 6 or 12V lamp and connect it to the output, and then adjust it to the 1.2v.
    If this has been done, then this output voltage can be connected to the 1.2v circuit.
    As input for this 1.2v circuit I have chosen to use the two 000 ohm resistors, basically the same as the previous voltage supply.

    Insofar as I have it working, and all the features of this test print work normally.
    But there is still to solve some small problem.
    The diode on the PCB get pretty hot, so the project is not completely finished yet.

    Dm800hd 1.2v replacement solution.jpg
    Wire Red is +5v, Blue is Gnd, White is the 1.2v + output to the circuit.

    It's working but it is still in the experimental state, so if you are planning to do it, do it on you're own risk.
    The text/photo's from this message may change if needed.

    Update..........
    After some more experiments by modified a second good working motherboard this way it seems not a good way as a alternative solution.
    My next test was to use 12v input, and adjusted to the 1.2v.
    This because when using the 5v as input, the total amps consumption rises, with 12v input it doesn't.
    But further it works, the receiver seems to work fine with this solution.
    However the Dc to Dc module becomes to warm/hot to use it for real.

    And so, be aware that this project is still experimental, it has some issues.
     
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  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    To come back to this project..
    Meanwhile I have tested this on a second motherboard to see if it makes a differences.
    Well, the Dc to Dc module becomes still warm but further it works fine.

    This time I have tested this by leaving it on for a week/24 hours.
    And the box is still working, so it could be a alternative solution for the 1.3v voltage delivery.

    Image of this project, click on the image for a normal view.
    Dm800hd-u23-24-25-alternative-solution.jpg

    And another picture is this, here you can see how much the 1.4v consumption is.
    It's adjusted to 1.4v and with the consumption it is 1.2v.
    But also a nice picture to see.

    Click on the image for a normal view.

    dm800hd-voltage-check-and-1-2v-external-delivery.jpg
     
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  3. tinoco

    tinoco New Member

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    [​IMG]
    To come back to this project..
    Meanwhile I have tested this on a second motherboard to see if it makes a differences.
    Well, the Dc to Dc module becomes still warm but further it works fine.

    This time I have tested this by leaving it on for a week/24 hours.
    And the box is still working, so it could be a alternative solution for the 1.3v voltage delivery.

    Image of this project, click on the image for a normal view.
    [​IMG]

    hello colleague Johnny B. excuse me once again to be annoying you just received the LM2596S DC-DC in my house and I have some doubts, can you explain me better how to connect to dreambox.
    1- I have to desolder the electrical components as in the image that here is correct.
    2- I have to connect the LM2596S DC-DC as it is here in the photos.
    3- The power supply to connect the dreambox will remain the same with the 12v.
    4- I have to regulate the LM2596S DC-DC for how many volts.
    Once again a big thank you for your help then I'll let you know if everything went wrong or well okay goodbye.
     
  4. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Questions,
    1, indeed.
    2, correct.
    3, You can use the 12v, or a 5v input supply, my example was with a 12v input source.
    4, You must adjust the output voltage level between the 1.2v/1.4v before you connect it to the 1.3v circuit.
    The ground you can take from any ground spot.

    Snap1.jpg
     
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  5. tinoco

    tinoco New Member

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    hello Johnny B I have a problem I think I turned off all the pieces but now when I am measuring with the voltmeter it is still the same whistle wherever the 12v
    Do you have any idea what it will be?
     
  6. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    I think, a short circuit to a internal layer, most likely the burned place 12v input sector.
    You need to clean it and to look with a good magnifier to find the short circuit, I use mostly my hdmi microscope to see were it creates a short.
    Nevertheless, it's not so easy to solve because there are at least two internal layers.
     
  7. tinoco

    tinoco New Member

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    I am measuring and I found the SMD capacitor C246 on the edge of the capacitors 2200mf 10v that au measuring is beeping and is measuring the same on both sides
     
  8. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Just remove a cap when you have doubts, there is often no other option to find the issue without removing some parts.