LG TV Power Supply low output voltage to led driver

Discussion in 'General Electronics Chat' started by Amir Eltahan, May 27, 2016.

  1. Amir Eltahan

    Thread Starter New Member

    May 27, 2016
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    Hey all,

    I found an LED TV and decided to try and fix it. It powers on and there's sound, and when I light a flashlight on it there's an image. I figured the backlight is broken so I measured the output to the LED driver with a dvm and it gives me an unstable reading (12 V, 10 V, 8V, etc.. down to 0V) in a cyclic manner.
    Any idea where to start looking? (all capacitors look ok). PCB is EAX64905301

    Thanks
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    Is this really an LCD TV with a duff backlight?
    If so, the first thing to do is to establish what kind of backlight it uses.
     
  3. Amir Eltahan

    Thread Starter New Member

    May 27, 2016
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    LED not LCD
     
  4. SLK001

    Well-Known Member

    Nov 29, 2011
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    You most likely have a few bad LEDs. You're going to have to crack open the panel.
     
  5. Amir Eltahan

    Thread Starter New Member

    May 27, 2016
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    I measured the voltages with the LEDs disconnected. My first guess is that the power supply board is faulty...
     
  6. SLK001

    Well-Known Member

    Nov 29, 2011
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    You can't get the voltage you want with the LEDs disconnected. The driver will interpet this as "LEDs OPEN" and flag a fault.

    You have bad LEDs. You're going to have to crack open the panel.
     
  7. AlbertHall

    Well-Known Member

    Jun 4, 2014
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  8. Amir Eltahan

    Thread Starter New Member

    May 27, 2016
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    When the LEDs are connected the blink every few minutes, with correlation to voltage peaks (what I described earlier). Does it make sense that the LEDs are faulty? The voltage measurements are
    I know, but since we deal with backlighting here, it is important to not that it's an LED TV (uses LEDs for backlighting..)
     
  9. AlbertHall

    Well-Known Member

    Jun 4, 2014
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  10. SLK001

    Well-Known Member

    Nov 29, 2011
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    All this depends on the TV's software. If the LED driver(s) sense a fault, they will shut down. The main software may wait for a few minutes, then try to reset everything, then LEDs on, fault detected, shutdown all over again, ad infinitum.
     
  11. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    What is the make and model of the TV?
    Can you post some nice clear picture of the back of the set?
    Have you checked all the voltages from the power supply? Post your results please.
    Capacitors can be bad even when they look good. Do you have an ESR tester?
     
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