Author Topic: LG 32LG5000 no back-lighting after one second.  (Read 3338 times)

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Offline taliban_0r

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LG 32LG5000 no back-lighting after one second.
« on: April 21, 2015, 07:00:41 pm »
Hello everyone,
I'm a Computer Science student from Portugal.

I've got here a LG 32LG5000 and I will make a list of what's going on for better organization. Then I will ask some questions.

Actually, while writing this I was dismantling the TV and I think I found the problem but I will post it anyway.
  • It displays image for only 1 second after turned on.
  • After the screen goes black but everything else seems to work (sound, remote, front LED).
  • Main PSU fuse is OK (took it off and checked it @ electronics shop).
  • There's a sound (like a switch) coming from a board on the left side (view from back) when the display goes off. (later fount it's the CCFL back-lighting board).
  • EU(PAL market).
  • I've found the service manuals.
As said, I dismantled the TV deeper and as far as I know that left side board holds the transformers for the CCFL back-lighting.
Then I proceeded to light up the panel with my phone LED flash and there was image!
So, the back-lighting board seems to be the problem (not sure yet). Maybe it's the other board that triggers the back-lighting that has a problem.

Questions:
  • Anyone knows if this is a common problem on this TV, brand... etc? Just curious.
  • What equipment should I borrow to test the backlighting board? (to be 100% sure).
  • How do I test this kind bulbs? (CCFL)
  • Where can I get a CCFL back-lighting module from a safe store? That ships to Portugal (EU).

Since this is my first post, my background in electronics is a class I took in a semester where I've learned to use equipment, and learned a bit about electronics itself.
 

Offline dundee

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Re: LG 32LG5000 no back-lighting after one second.
« Reply #1 on: April 21, 2015, 08:02:42 pm »
    • What equipment should I borrow to test the backlighting board? (to be 100% sure).

    Hi!
    You should have a soldering iron and multimeter.

    Probably a protection circuit is turning off the backlight, because of a shorted transformer.

    Check the transformers. If there is one ore more with shorts, you could replace them...[/list]
     

    Offline taliban_0r

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    Re: LG 32LG5000 no back-lighting after one second.
    « Reply #2 on: April 23, 2015, 07:52:37 pm »
    Quote
    Hi!
    You should have a soldering iron and multimeter.

    Probably a protection circuit is turning off the backlight, because of a shorted transformer.

    Check the transformers. If there is one ore more with shorts, you could replace them...
    Thank you for your answer!
    So... there is this brown stuff, doesn't seem it's supposed to be there.


    What kind of products are safe to clean this?
    « Last Edit: April 23, 2015, 07:56:46 pm by taliban_0r »
     

    Offline dundee

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    Re: LG 32LG5000 no back-lighting after one second.
    « Reply #3 on: April 23, 2015, 10:19:28 pm »
    The brown stuff is not the problem. You can clean it with isopropyl alcohol.

    I think one or more of the trafos were broken.

    You have to check the resistance of the coils with a multimeter.

    You can geht them as spare parts here:
    http://www.amazon.de/Inverter-Trafo-4018L-Darfon-Inverterboard/dp/B00MWRK0C2 (Germany)

    //EDIT:
    Checkout this:
    http://www.lcdparts.net/TransformerDetail3D.aspx?ProductID=3497

    Secondary Resistance should be 1.10 K and
    Primary Resistance should be 0.5 Ohm

    You can see the pinout of the trafo in the picture.
    « Last Edit: April 23, 2015, 10:27:48 pm by dundee »
     

    Offline Rasz

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    Re: LG 32LG5000 no back-lighting after one second.
    « Reply #4 on: April 24, 2015, 07:34:50 am »
    You can geht them as spare parts here:
    http://www.amazon.de/Inverter-Trafo-4018L-Darfon-Inverterboard/dp/B00MWRK0C2 (Germany)

    holy crap, thats the price of a whole replacement inverter :D
    Who logs in to gdm? Not I, said the duck.
    My fireplace is on fire, but in all the wrong places.
     

    Offline taliban_0r

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    Re: LG 32LG5000 no back-lighting after one second.
    « Reply #5 on: April 25, 2015, 09:00:47 pm »
    The brown stuff is not the problem. You can clean it with isopropyl alcohol.

    I think one or more of the trafos were broken.

    You have to check the resistance of the coils with a multimeter.

    You can geht them as spare parts here:
    http://www.amazon.de/Inverter-Trafo-4018L-Darfon-Inverterboard/dp/B00MWRK0C2 (Germany)

    //EDIT:
    Checkout this:
    http://www.lcdparts.net/TransformerDetail3D.aspx?ProductID=3497

    Secondary Resistance should be 1.10 K and
    Primary Resistance should be 0.5 Ohm

    You can see the pinout of the trafo in the picture.
    The readings I got were:  :-DMM
    ~1.010K Ohm on the primary.
    ~0.5 Ohm on the secondary.
    No shorts found.

    If this is some tiny component on that board I'm f.


    There is one of them that is on the 0.9K (pink @ picture)
    The area marked in RED on the picture above is contaminated with some fluid from that yellow sponge.
     

    Offline wraper

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    Re: LG 32LG5000 no back-lighting after one second.
    « Reply #6 on: April 25, 2015, 09:11:02 pm »
    The readings I got were:  :-DMM
    ~1.010K Ohm on the primary.
    ~0.5 Ohm on the secondary.
    You messed up primary and secondary.
     

    Offline wraper

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    Re: LG 32LG5000 no back-lighting after one second.
    « Reply #7 on: April 25, 2015, 09:18:12 pm »

    There is one of them that is on the 0.9K (pink @ picture)
    Should be faulty with a short in the secondary winding. There must not be any significant difference in resistance among transformers.
     

    Offline iamdarkyoshi

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    Re: LG 32LG5000 no back-lighting after one second.
    « Reply #8 on: April 26, 2015, 12:43:08 am »
    I had an Envision monitor with the same fault, but unbelievably, it turned out to be a CRACKED backlighting tube and it was ARCING TO THE CHASSIS!!!! I removed the tubes and just put a strip of cool white LEDS inside and found the logic line that turned the backlighting on. Works a treat.
     


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