DM800HD shows green screen after a while

Discussion in 'DM800HD Hardware troubles and Repair support.' started by mpro, May 17, 2017.

  1. mpro

    mpro New Member

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    Hi
    I Own a DM800HD (original, not clone), that shows a green screen after working for a while. It could be 1h, 2h, or a few minutes. Its a random problem. After the green screen the box reboots by it self and starts working good until the next green screen.

    A have made the following experinces and none of these changed this behaviour (green screen)
    1) Replacing the power supply by a new one.
    2) Using diferent software images (gemini, openpli, etc)
    3) Inserting a heat sink in the processor to lower operating temperature
    4) Inserting a fan to improve cooling.
    5) Erase/Identify bad sectors.

    The log associated with the green screen not show a unique cause (is random).
    I think that this is a HW problem but I cannot figure where is the problem. The capacitors have good looking. Could be Flash and/or memory failure/issues?
    Does any of you had a problem like this?

    Best regards
     
  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    I'm first thinking of to many bad blocks on the nand flash chip which often cause it.
    With dreamup, above xtra, enable the bad sector option, upload a normal image file.
    When you have bad blocks, repeat it until it gives no more bad blocks.
    If your image file is bigger than the good blocks, use one which takes less mb's.
    Or replace the nand flash chip for a new one if you have to many bad blocks.
     
  3. mpro

    mpro New Member

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    Hi,
    Thanks for your answer.

    My box only indicates one bad sector. I uploaded openpli 2.1 with dreamup (with the option to recover bad sector extra checked ). Each time I flash an image with this extra option checked, the dreamup indicates the bad sector. It's suppose to be eliminated?

    I also flashed new image with the browser (with the option "Flash Sector Recovery" previously enabled in the bios of the box), and during flashing also indicates the bad sector in browser.

    Is suppose the bad sector been permanently eliminated? Instead of apearing each time I flash the box with the bad sector extra option checked ?

    Best Regards
     
    Last edited: May 17, 2017
  4. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Yeah, normally is one bad block not a issue, even five blocks are not a issue if the software are be able to mark the bad blocks and writes the software to the good sectors.

    However in rare cases a nand flash chip refuses to mark bad block due a error of the chip or jumper resistor.
    In that case it's better to check if the zero resistors are present near the chip, and on the right place.

    When I thinking of another case than the nand chip, then I'm thinking of the TL7702A U18.
    But when there is a issue with it, then it mostly reset the box and not a crash.

    A crash mostly happens due a bad nand flash chip, or due the cpu, or voltages to it as the U7, the 2.6v which is 2.3v.
    Or the 1.3v caps, C112/C113/C114 needed to be replaced for fresh ones.
     
  5. mpro

    mpro New Member

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    Hi
    Many thanks for your answer
    Can you please explain with more detail this: "
    However in rare cases a nand flash chip refuses to mark bad block due a error of the chip or jumper resistor.
    In that case it's better to check if the zero resistors are present near the chip, and on the right place.
    "

    If there is a problem in nand flash, could this problem be mitigated by using an external USB memory to load the firmware?

    Best regards
     
  6. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    There are some jumper resistors as the R170 near the nand flash chip, and on the parts side near the bios rom the R129 which must be present for the nand chip, sometimes they are interrupted.

    if a firmware can be loaded by the usb I don't know, never tried or figured it out.
    But to me it seems plausible, however I would first try it with dreamup and enabling the bad sectors option instead of the bios option.
     
  7. mpro

    mpro New Member

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    Hi
    I already have tried with dreamup, with the bad sectors option enabled.

    Tried again and the results are:
    +++006 erased failed at 02b84000 e1. Block will marked as bad
    +++006 erased failed at 03ff8000 e1. Block will marked as bad

    Many thank
    Best Regards
     
    Last edited: May 17, 2017
  8. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Hmm okay well normally may a flash chip have 10% bad blocks, so not really something to be worry of.
    And you could do a test with a image file which has less Mb's to upload, and uploading with a browser may also help.
    That is, if it's caused due bad data readings.

    Another test is to test the box with and without the tuner, and playing a movie file from a usb stick to see if it stays working.

    And else, it could be a hardware issue with some cpu voltage (1.3/2.6 or 3.3v) which is to low or to weak due bad caps or you use a weak power supply as a 2 amps one.
    The box works the best on a 4 or 5 amps psu, at least a 3 amps.
     
  9. mpro

    mpro New Member

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    Hi JB
    Can you please show me where are the C112/C113/C114 CAPs in the Board?
    Can you please show me where is the NAND flash chio and the Jumper Resisstors?
    Can you please upload a picture showing this?
    Best Regards
     
  10. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    toysoft likes this.