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LG 47LN5750 No picture

Have audio and have done flashlight test - I can see image with flashlight - no backlights. Have replaced T-Con board and Power Supply believe LED Driver is built in to Power Supply - Next Step?

Posted by Vern Laing on

  • 6 more comments 
  • Vern Laing
    Vern Laing Nov 28, 2017

    Thanks Larry - does that mean I may have shorted the new power supply board I installed? - Is the next step to replace one or more of the LED strips? I'm not sure what you mean by servicing the LED light circuit.

  • Larry Nov 29, 2017

    Your replacement power board should be ok as long as its not run for hrs without backlights. Do you have a volt meter?

  • Vern Laing
    Vern Laing Nov 29, 2017

    Yes I do - I watched the You tube video and connected it accordingly - doesn't register any voltage (checked voltmeter and its OK). I think it show some voltage for a split second when I turned it on.

  • Larry Nov 29, 2017

    If you disconnect the connectors going to the main board does the LED's light up?

  • Vern Laing
    Vern Laing Nov 29, 2017

    No they don't

  • Kevin Romleski
    Kevin Romleski Dec 13, 2017

    sounds to me like bad leds on the strips

  • Larry Dec 13, 2017

    He has already changed them.

  • Vern Laing
    Vern Laing Dec 16, 2017

    Yes - I have replaced the T-Con Board, Power Board and all 12 LED strips. I don't think there is anything left to replace other than the main board but I can still see an image. I show maybe 1 volt on one side and 1/2 volt on the other side going to the strips. Any other
    ideas?

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2 Answers

Larry

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If you have backlights its not going to be the tcon for future reference. you have some shorted or open LEDs in the panel. Check the voltage going to the LED sets, should be 100 plus volts

Posted on Nov 16, 2017

  • 13 more comments 
  • Vern Laing
    Vern Laing Nov 28, 2017

    The voltage is near zero on both sizes (although I don't have a tester with Min/Max setting). Just wondering if the 100V is continuous and I need one with the min/max setting? Also would I be able to use a 12V battery charger to check if the LEDs are burnt out?

  • Larry Nov 28, 2017

    You don't need a meter with the min max setting, that voltage should be there at all time. The voltage will vary depending on the amount of LED's in the panel...some sets run as low as 60 and some get up to over 150 but if you have nothing with the plug unhooked you have a bad power supply board, depending on how much experience you have in electronics the LED light circuit on the power board isn't that hard to service and usually can be fixed for a couple bucks

  • Larry Nov 28, 2017

    There is still a possibility the board was damaged by shorted LED lamps and a new power board won't solve your issue

  • Vern Laing
    Vern Laing Nov 28, 2017

    Thanks Larry - I'm not sure what you mean by servicing the LED light circuit. Since I installed a new Power Supply is the next step to find a burnt out LED strip(s)

  • Larry Nov 29, 2017

    There is no doubt you have some open LED lamps inside the panel, the lamps are all wired in series like the old Christmas lights used to be, if one goes out the entire string is out. I did look at the service bulletins on this set and its prone for lamp failure. You can order new strips from shopjimmy but they aren't real cheap and a pain to change

  • Vern Laing
    Vern Laing Nov 29, 2017

    That's what I thought - thanks for your help - I'll give it a shot - learning exercise - I know there are 12 strips - what's the chance that's it's just one strip? - Probably easier just to order all 12 eh?

  • Larry Nov 29, 2017

    The problem with LED sets is the lamps in the panel are basically a 2.5 to 2.8 volt lamp depending on what bulb is used but they are driving them at around 3.3 to 3.5 volts with the backlight setting at 100 and that is the factory setting, this is just my opinion but I think the engineers set the backlight setting at 100% intentionally to reduce the life of the lamps making the sets only last a couple yrs on avg. Ive got 4 LED TVs that are all several years old and not a one has given me issues but I reduced the setting to 75% when I bought them. I'm seeing about half the sets that come in for service that are over 2 yrs old having backlight failure, its kind of sad. I do reduce the setting to around 80% on the sets I work, not sure how much that will help since they have been running at full brightness for the age of the set but figure its going to help some.

  • Larry Nov 29, 2017

    You can resell your power board and T-con on ebay if you want to get at lest part of your money back instead of throwing it away with the set.

  • Vern Laing
    Vern Laing Nov 29, 2017

    Great - I've just stripped it down to get the part numbers from the strips - if I get it working I'll take your suggestion on the settings. The youtube video was great. I don't have a way to test the strips so I'll just order the set.

  • Larry Nov 29, 2017

    Its best to order the entire set anyway, be really careful when removing the panel as the thin flat connectors that go to the tcon board can be damaged really easily and chances are you won't know they were damaged tell you put the set back together and find a part of the picture missing or distorted, also the various layers of film all need to go back in the order they were removed or it won't work right.

  • Vern Laing
    Vern Laing Nov 29, 2017

    Got it - parts ordered - good news that if it doesn't work I get a better larger TV. Just couldn't see tossing out a 3 year old TV without trying. Appreciate your advice - thanks again.

  • Larry Nov 29, 2017

    Your welcome!...good luck

  • Vern Laing
    Vern Laing Dec 12, 2017

    Well Larry - installed the LED strips and didn't solve the problem. Still see image with flashlight. Now to sell all the parts I purchased (LED strips, T-Con and Power Supply) unless you have another suggestion? Good for parts now but it was interesting to see how things are put together and how cheap parts are for TV's. I'll make sure I turn down the backlights to 75 or 80% on my next TV. Cheers

  • Larry Dec 12, 2017

    Refresh my memory, did you say you had about 100 volts going into the LED lamps from the power board?

  • Vern Laing
    Vern Laing Dec 13, 2017

    No - I had zero. Put the set back together and I can see the image with a flashlight still.

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blossom5055

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Soory gtg I will answer that later ok

Posted on Nov 29, 2017

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olga8004

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SOURCE: No back-light on LG LED TV

That means dead transformer supply chain. Replacing search not possible, donor Yes

Posted on Aug 08, 2016

gopakumarg43

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SOURCE: LG 50la6970 no backlight i have sound and dark images!

Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis. http://electronicshelponline.blogspot.com/ To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.

Posted on Oct 08, 2016

AJIN G

Electro Med Services

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SOURCE: LG LED TV. 50LN5700UH. Picture out. It will flash LG Logo on power up then go black. Image is present by flashlight test. Audio is also present. Power LED is also lit.

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis. http://electro-medical.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.

Posted on Jan 02, 2017

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