DM800HD SE clone Problem

Discussion in 'Hardware troubles and Repair support.' started by tomgr, May 13, 2021.

  1. tomgr

    tomgr New Member

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    Good evening and welcome!!
    I have the DM800HD SE clone.
    When I turn it on, I get the following results:
    The problem is shown in the two compressed files with the tuner mounted and without tuner.
    And here are the values from the measurements:

    Any help is welcome...
    Thanks!!
     

    Attached Files:

  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    3.3v 4 75 ohm versus 1744 ohm seems to me a issue with the 3.3v section.
    I think, remove the tuner/front panel and check the ohm value again.
    With no improvement then just to be sure remove the sim card and check it again.

    Last option is to remove the bios rom and check it again but be aware that it is not easy to remove out the socket, you normally need a special tool for it.

    In any case, every part that uses this voltage could be responsible, even the cpu.
    But it could also a issue with the Dc to 3.3v step down converter. maybe the chip itself or just a damage 3R3 L1112 coil.
    Check at least the ohm value before and after it, they should be the same.
     
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  3. tomgr

    tomgr New Member

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    Good evening again.
    I managed to start the receiver, resting my finger close to U1100.
    Unfortunately, trying to fix it, the Q1100 burned out.
    I tried to apply the method described here:
    https://jb8a8f8.com/support/index.php?forums/schematic-drawings-pcb-images-etc.13/
    but there must be some short circuit, because the measurement on pin 5 gives results 0 ohm.
    I tried to locate the component that creates the problem without success.
     
  4. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    If/when the 5v circuit is totally shorted as if it's directly connected to ground then it will be a though job to find or fix it because it can be everything connected to the 5v circuit, or the 5v delivery circuit has been damaged.

    You can disconnect some circuits from the 5v circuit by removing some inductors, or zero ohm resistors as the R1150 to disconnect the U1103 etc.
    But if you do, check only the 5v circuit by ohms measurements, and never power up the board when removed, otherwise you may risk to create more damage.
     
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