Question about LG 37LC7D 37 in. LCD HDTV

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I have an LG 37LC7D, whenever I turn it on once its been sitting unplugged for a while, it comes to life perfectly for about 3 secs (can see video signal) then the screen shuts off for 3 secs, turns on for 3 secs, and repeat this 3 sec cycle about 10 - 15 times (green power light stays on entire time) before it seems to give up and turn itself off. Ive had the back off, there seems to be some squealing from the large black angled transformer on the power board each time it blinks on for 3 secs. (the best way to describe the sound is like the way a modem sounds while handshaking or faxing, just much quieter). if i keep trying to turn it on, it will turn on for 3 secs, then the screen will just shut off completely, green power light stays on for a while, then eventually turns red (off)

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  • Rommel Cana
    Rommel Cana Sep 28, 2010

    it only means that there is something that hinders the power supply from turning ON

    completely. Use a Multimeter to measure PSU output voltages

    to facilitate and diagnose properly , you need a service manual to guide you,

    only with a fee

    And bleed ( discharge ) the power capacitor with a 4.7K 5W resistor , when having

    a resistance check ( to be safe )

  • aekirwin Sep 28, 2010

    As a computer tech, im more into component swapping, not circuitry. im wondering if the issue is the power board or a ballast or something (maybe inverter). i found a replacement powerboard on ebay, but unlike troubleshooting computer hardware, im not positive about my diagnosis:P. Laptops have a small inverter that jacks up the voltage for the ccfl, however at first glance, it looks like this powerboard (p# EAY34796801) has an integrated inverter (the squeeling transformer), or is this just the first step before the high voltage gets carted off into the screen and jacked up even further by actual inverters that are out of view? the cables that go from this powerboard to the LCD look like larger versions of the unique wires that go from the inverter to the ccfl in an LCD on a laptop.

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    same principle applies, remove the load from the power supply , to see where it acts up

    more details can be found on the service manual

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    on the upper left side of the image :

    you can measure the voltages on it, and post what you got,

    if the unit is in standby and when you try to turn it ON

  • aekirwin Sep 28, 2010

    had it unplugged for a while, turned it on, stayed on for about 5 mins, started to flicker with zappy sounds from the large transformer on (bottom right of that image) whenever it flickered, after a few more flickers, it powered down. the contacts on the top left image that you are refering to go to the image processing board, which from what i can tell functions perfectly. are there inverter boards inside the panel, or is that zapping transformer the actual inverter for the ccfl? i bought that service manual but it was not very helpful (my understanding of circuitry is severely lacking). i was more hoping maybe you can identify and confirm the power board as the cause so i can just buy a new one:P can a failing ccfl tube cause this in a tv? (cant on a laptop) if i were to compare these symptoms to a laptop, id be absolutely positive its inverter. what i havent been able to identify is if the power board has the inverter built in, or are they built into the panel where i cant see them without taking the tv apart further, and possibly malfunctioning causing the effects (buzzing from transformer) that i see on the power board. in which case if i replace the power board, I've got the same issue. I truly appreciate all your help.

  • aekirwin Sep 28, 2010

    id be happy to email you a hi res pic of the back of the tv, a low res vid of the tv in action, and the repair manual if you had some spare time....

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    you can send a link where I can view , to help you further , and i need the voltage measurement

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    you will have to check the P_ +19V

    + 12V

    + 9v

    + 6v

    ST 5V

    3.3 V

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    on page 8 of your service manual you can see that the

    LVDS is powered by 12V

    Try to find that line , and disconnect the 12 V that goes to the Inverter,

    Be fast enough to catch the voltage , it drifts easily,

    ground or connect the negative of your Multimeter to the chassis

    ( when measuring voltages )

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    i mean page 18

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    then follow the flow diagram on page 19 ,

    and post what you found

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    EAY34796801 is only a power supply board

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    your inverter board may look like these :

  • Rommel Cana
    Rommel Cana Sep 28, 2010

    Please be guided that the Inverter Output Voltage can reach over 1.2KV ( ballast )

    if it is working



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Do not keep forcing this unit on - - This particular unit has a VERY commonly known problem and there are at least five tech bulletins from LG explaining this and other symptoms for the failure. In a nutshell there are coils that have to be removed and replaced with a jumper wire. This is not a repair you want to tackle so please get some experienced help for this one. A good technician will look-up the bulletins and educate themselves on the manner of the repair.
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Hope this helps!
William Rayburn, CET
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Aug 03, 2009 | Televison & Video

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