Question about Samsung LNT4066F 40 in. LCD Television

2 Answers

Samsung LNT4066F, backlight is out

When I turn on my LNT4066F, the backlight comes on for a couple of seconds and then goes out. TV stays on, and if I hold a flashlight at 45 degree angle I can see a picture, sound works fine, and blue power light stays on.
What do i need to replace or repair?
Thanks in advance

Posted by on

  • 7 more comments 
  • Greg Bonhotal Apr 27, 2010

    is there a way to verify inverter board is bad?
    I have checked resistance of all transformers on inverter board,and they are all around 3oo ohms.
    I have multimeter, and am willing to trouble shoot.

  • Greg Bonhotal Apr 27, 2010

    I do not want to REPAIR inverter board, I just want a way to be sure that the board is the problem and not the POWER SUPPLY BOARD, since the high voltage transformer is on the power supply board, as well as a low voltage cable that goes to the inverter board.
    I just want to be sure that everything else is working, before the inverter board.


  • Greg Bonhotal Apr 27, 2010

    Hi,
    I do not want to REPAIR the inverter board.
    I just want to know if there is a way to be sure board is bad.
    I don't want to replace it and then find out that the POWER SUPPLY BOARD is bad.
    Ther is a low voltage cable that goes from the power supply board to the inverter board.
    There is also a high voltage transformer on the power supply board, that powers the inverter board.
    What is the likelyhood that replacing the inverter board will fix this issue?
    Thanks


  • Greg Bonhotal Apr 28, 2010

    Hi, Thank you for responding,
    I feel like I finally found someone who is an expert on samsung.
    My the sticker says model code = LNT4066FX/XAA
    version = SS03

    When I hold the non contact voltage tester over the HV transformer, if beeps for the 1.5 seconds the backlight is on, and then stops when the backlight goes off.
    I could not find anything marked (CNM802 & CNM803) but i did check the power connector called CNI803 that runs from the power supply to the motherboard.(5 pin).
    on that connector pin 1 inverter on/off stayed at 5.28 v
    pin 2 - dim . starts at 3.5v then goes to .63 while backlight is on then slowly climbs to then to .82v after backlight goes off. where it stays.
    pin 5 stays at 5.39 v no matter what.

    not sure where the 24 volts is, but, if it is supposed to be on this connector it is bad.
    if it is on a connector between 2 boards which 2 boards would it be?
    if a testpoint or lead of a cap, which one?

    Thanks, I think we are almost there.

  • Greg Bonhotal Apr 28, 2010

    Hi, Thank you for responding,
    I feel like I finally found someone who is an expert on samsung.
    My the sticker says model code = LNT4066FX/XAA
    version = SS03

    When I hold the non contact voltage tester over the HV transformer, if beeps for the 1.5 seconds the backlight is on, and then stops when the backlight goes off.
    I could not find anything marked (CNM802 & CNM803) but I did check the power connetor called CNI803 that runs from the power supply to the motherboard.(5 pin).
    on that connector pin 1 inverter on/off stayed at 5.28 v
    pin 2 - dim . starts at 3.5v then goes to .63 while backlight is on then slowly climbs to then to .82v after backlight goes off. where it stays.
    pin 5 stays at 5.39 v no matter what.

    not sure where the 24 volts is, but if it is supposed to be on this connector it is bad.
    if it is on a connector between 2 boards which 2 boards would it be?


    Thanks, I think we are almost there.

  • Greg Bonhotal Apr 28, 2010

    Thanks,
    You ROCK, It is wonderful dealing with a TRUE PROFESSIONAL!
    Thanks for ALL Your Help and Patience :)


  • Greg Bonhotal Apr 28, 2010

    This Guy Knows His Stuff, and knows How to Explain it to layman. He3 is a True Professional and a GURU!
    Thanks For your help.

  • Greg Bonhotal May 01, 2010

    Hi again,
    I replaced the power supply and it still does the same thing.
    when I check the connector on the inverter, I get 12v steady at vcc,
    ld starts at 10.18, and then goes to almost 0 while the backlight is on, and then once light is out it goes back to 10v]
    the others don't seem to have any voltage.
    Not sure where to go from here, any suggestions?
    Thanks



  • Greg Bonhotal May 06, 2010

    Hi again,
    I replaced the inverter, and still getting the same behavior.
    If I disconnect one og the high voltage wires, It still lights up for the same amountof timebefore going out. (1.5 sec)
    Is there a way to diagnose and/or repair or replace a bulb?
    Not sure how to proceed.
    Thanks,
    Greg



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  • 416 Answers

You need to make sure the 24v supply (CNM802 & CNM803 on the power supply) is staying up when the backlight drops out. You will be able to see the light through a few holes if you have the TV on its face with the back cover off. If the 24v stays steady and is not bouncing more than a few volts, your power supply is OK.

Next, you need to find the Sw-Inverter (5 wire cable to power supply) signal which comes from the main PCB. See if stays HIGH (5v or so).

Last thing... you need a tool... a cheap AC detector:
Samsung LNT4066F, backlight is out - a4296ee.jpg You need to see if the inverter transformer is staying ON:
f96899f.jpg Put the pen next to it and see if it still detect high voltage when the backlight shuts down.

If you have the 24v and it's good... and the ON line is good... and you have HV detection on the inverter transformer, you have a bad CCFL tube in the backlighting system. If this is the case, you would have to replace the panel. If the 24V line is bouncing around and dropping more than a few volts or your HV detection drops out, your power supply is bad. If the ON line is cutting out, you probably have a bad main board... inverters don't typically feedback errors to the main board. So if the main is shutting the ON line down, it's suspect. I hope this was helpful, best wishes.

Posted on Apr 27, 2010

  • 3 more comments 
  • Adam Halfhill
    Adam Halfhill Apr 27, 2010

    If you need part numbers, supply the full model and version code from the side sticker (side of rear cover).

  • Adam Halfhill
    Adam Halfhill Apr 28, 2010

    The secondard supply that is feeding the transformer or the transformer has a problem. And with that said... replace the power board, PN: BN44-00167A. You should be set.

  • Adam Halfhill
    Adam Halfhill Apr 28, 2010

    Glad to help, hit me with some thumbs :)

  • Adam Halfhill
    Adam Halfhill May 02, 2010

    Sorry, I thought we had it. This model and those of the same production year split the ballast up. Some of the function is on the power board (that transformer you checked with the ac detector) and the rest is on the ballast. Maybe the power supply is going into a current protection mode. The only real meat on that ballast board are the transformers that directly feed the lamps. Disconnect the ballast from the TV and do some measurements. Check the resistance (in circuit) of each transformers output terminals. You may be able to check this on the lamp connectors. See if 1 of them is different then the others. If they are all the same, you may have a CCFL lamp that is dead.

  • Adam Halfhill
    Adam Halfhill May 07, 2010

    The road has come to an end and there are no paths to follow short of changing the panel. To purchase a panel at this point would be borderline crazy. The best advise I can now give you is to call upon your favorite online auction site. Sell the TV part-by-part to maximize your return. Do yourself a favor and sell the LCD panel "as-is" and make a note that it has a bad lamp. Not sure if it will sell, but you never know. Include the Model and Version number of the TV when you list the part, along with the part number. Sell the Screen frame, Rear Cover, and especially the stand, people misplace those and often try to purchase them. Best of luck, I hope it all works out.

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  • 10,594 Answers

Hi,
Replace back light inverter board to get continue back light to view lcd screen image.
Back light inverter board turns off for some reason and no schematics are available to repair it on component level so have to replace complete board.
Check with local tv repair shops as they might have spare board for you.
Hope this info will help you.
Thanks.

Posted on Apr 26, 2010

  • 1 more comment 
  • Shahid Electronics
    Shahid Electronics Apr 27, 2010

    Without schematics, troubleshoot is not possible and if you find out few defective parts, will not be available as individually because inverter boards are not suppose to be repaired on component level.

  • Shahid Electronics
    Shahid Electronics Apr 27, 2010

    I do not want to REPAIR inverter board, I just want a way to be sure
    that the board is the problem and not the POWER SUPPLY BOARD, since the
    high voltage transformer is on the power supply board, as well as a low
    voltage cable that goes to the inverter board.
    I just want to be sure
    that everything else is working, before the inverter board.
    =======================================================================

    OK, in low voltage cable/ connector, please check back light error signal, if that pin goes high that means inverter board generate that signal due to internal problem and this signal goes to main board (system control chip) to turn off back light inverter supply.
    It would be fine if you post here low voltage connector label/ names to point out back light error pin.



  • Shahid Electronics
    Shahid Electronics May 01, 2010

    Hi again,
    I replaced the power supply and it still does the same
    thing.
    when I check the connector on the inverter, I get 12v steady
    at vcc,
    ld starts at 10.18, and then goes to almost 0 while the
    backlight is on, and then once light is out it goes back to 10v]
    the
    others don't seem to have any voltage.
    Not sure where to go from
    here, any suggestions?
    Thanks
    ==========================================================

    Please replace back light inverter board.



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