faulty power board

Discussion in 'Technical Repair' started by kkaro, Mar 20, 2017.

  1. kkaro

    Thread Starter New Member

    Mar 20, 2017
    2
    0
    Hi, it looks like there is blown up resistor on the led tv power board. I want to replace the whole board but wonder what might have caused the damage (shown on the pic). How did it happened. Is it internal TV problem (5 years old tv) or rather external issue, power supply? Is it worth repairing it and is there a way to prevent similar damage in the future.
    tmp_20449-IMG_20170304_1215341977735132.jpg tmp_20449-IMG_20170304_104307-1060553971.jpg
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    13,441
    3,763
    A schematic for the set would be a help in diagnosing what the cause could have been.
    There are some sites that offer schematics for some makes.
    Max.
     
  3. wayneh

    Expert

    Sep 9, 2010
    13,747
    4,518
    There's a decent probability that one of the electrolytic capacitors has failed. You could mess around testing and diagnosing them all but the reality is that it's faster to just replace them. They go bad over time and the ones under stress (a lot of AC current) will eventually go bad even if they haven't yet, so replacing them is not a loss, and might fix it.

    I used to think this recommendation was nutty but I've become a believer.
     
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  4. LesJones

    Active Member

    Jan 8, 2017
    709
    143
    It looks like the resistor is on the primary side of the switch mode power supply. The IC next to it is the switch mode controller IC. (Link to datasheet) I suggest tracing out the schematic of that part of the board to see what that resistor does. There is an example schematic on the data sheet so it should be possible to identify it's function. I think the fault is internal to the power supply rather than excessive load on one of it's outputs but I would do some investigation to confirm or disprove that susspicion.

    Les.
     
  5. AlbertHall

    Distinguished Member

    Jun 4, 2014
    4,608
    1,060
    Yes, that resistor is likely connected to that IC's MOSFET source as the current sense resistor. It happens that such MOSFETs go short circuit and that would destroy that resistor. Usually when such things happen in switch mode power supplies that other components will be damaged. What makes these supplies difficult to repair, even for those experienced in such things and having the schematic, is that if fail to find one of the damaged components then it will go bang again when powered up.
     
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  6. kkaro

    Thread Starter New Member

    Mar 20, 2017
    2
    0
    Thank you for your answer. So would you advise to replace the power board only? Or mother board might be affected too (no visible damage on other boards)
     
  7. AlbertHall

    Distinguished Member

    Jun 4, 2014
    4,608
    1,060
    The damage is probably restricted to the power board but there is no guarantee of that without experience of this board.
     
  8. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    6,555
    1,052
    It's a Smpsu chip A6052m, note Pin6 is missing deliberately...
    The resistor will be connected to pin 1 current sense.


    str-a6052m_tcd_en.png
     
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