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LCD backlight problem? inverter problem? SHARP

Discussion in 'Repairing Electronics' started by dirtyb15, Jun 4, 2009.

  1. dirtyb15

    dirtyb15 Member

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    Hi all. i Have an older sharp lcd tv 37" that someone just gave me because it has an intermittent backlight problem. It is in great shape otherwise so id like to fix it if i can. Basically the backlight wont turn on 19 out of 20 times when you power the tv up. Eventually if you unplug it and plug it in it will turn on , and its fine till you power the tv off.
    When it finally does turn on it says it had a lamp error and i have to reset the error.
    I really dont want to leave it on 24 hours a day and im hoping i can fix it. Does this sound like a faulty inverter? If so, can this be repaired or do i need to find another board?
    Thanks in advance for any help.
     
    Last edited: Jun 4, 2009
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You don't mention the model?, but - and you'll probably like this! :D - a number of the older Sharp models had a problem with the earthing screws on the inverter becoming loose, causing it to shut down. You can simply make sure they are tightened properly, or Sharp provide some modified screws to replace them, basically screws with shake-proof washers built-in.

    If that doesn't cure it, again depending on model, on some you need to replace the large string of opto-couplers on the inverter board.

    But if you're lucky, it's just the screws.
     
  3. dirtyb15

    dirtyb15 Member

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    Thanks for the reply nigel, ill try that!. The set is at home or i would have posted the model number (cant remember off hand.) It has the seperate box for inputs ect, so it is older.
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    As you're the other side of the Atlantic the numbers are likely to be completely different anyway.
     
  6. dirtyb15

    dirtyb15 Member

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    Well, there are 4 inverter boards, and i tightened all the screws (seemed tight already), and same symptoms. What should i check next? I have the model number now, its a LC-37HV4U
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The European models are LC-37HV4E and LC-37HV4EB, I've checked the technical bulletins, there's nothing listed on either of those two models.

    Do you have the circuit diagram?.
     
  8. dirtyb15

    dirtyb15 Member

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    I do not, ill start my search.
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    If you PM me your email address, I can send you the European manual - assuming your ISP allows large attachmanets.
     
  10. dirtyb15

    dirtyb15 Member

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    Thanks a bunch Nigel, i got the manual now. I have been going through the troubleshooting diagram, and the code does indicate backlight not lighting up.
    The next question is whether or not there is a control signal appearing at pin 2 and pin 3 of P7506 and P7616. Now, i measured these pins when I got the backlight to turn on, and pin 2 was 15 volts, and pin 3 was 4.4 volts. (on both P7506 and P7616)

    When the backlights dont turn on and i measure these pins i get 15 volts on both pin 2 and 3.

    Any ideas?

    I assume this means there is no control signal when the backlights are not on. If this is the case the manuals says to

    Check the circuits around IC4501
    in the main unit and check the
    operation of Q7704 and Q7705.

    I can check Q7704 and 7705, but what circuits should i be checking? Would there be something more prone to intermentent operation than total failure?
     
    Last edited: Jun 5, 2009
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Sorry, I've never seen one of those sets - but all LCD manual's seen pretty unhelpful in telling you what the feedback from the inverter is supposed to be.

    One thing you might try, is resistance measurements of all the transformers - apparently a common fault on many sets is transformers going O/C or high resistance - but personally, I've never seen one fail.
     
  12. Yetiman

    Yetiman New Member

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    Same Boat

    Hi Guys
    I was recently given the same model of Sharp 37" LCD in wont fire up condition, and came across your posts during my searches for info. It has fired up in the service mode (Vol- and Input held down while turning on the power) a number of times, but it is very hit or miss and stubbernly refusing lately. I've had the power supply pcb and the video/logic board out checking for cracked solder joints and cleaned all the connectors with Deoxit, but none of that helped. I'm going to order a bunch of those PC123 optoisolators and see if that makes a differance, but I am at the point were I really need a sckematic/service manual to figure out whats going on with it. Any chance one of you fine gents could sent a pdf my way? I would be ever so greatfull! Big files are Not a problem. Thanks a Bunch!
    Art
     
  13. unclejed613

    unclejed613 Well-Known Member

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    one thing that i've seen that causes backlight problems intermittantly is the high voltage wires from the inverters leaking to ground where they get pressed up next to the sheet metal. teflon tape around the pinch points seems to help, or you can take teflon plumbing tape and cut it into strips and lay the strips down overlapping and use clear packing tape to hold the teflon tape down to the sheet metal. teflon has a higher dielectric strength than black electrical tape. or you could paint the areas of sheet metal with corona dope.
     
  14. pacchu

    pacchu New Member

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    i too have an lg ly 95 42" lcd tv which when switched on works perfectly fine for a few minutes and then the the video flickers a few times and thereafter the video goes off whilst the audio is intact. i have been trying to find a solution for the problem, pse advise if anyone has a solution
     
  15. pacchu

    pacchu New Member

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    nigel i would be grateful if u have an idea as to what is the problem
     
  16. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I would image it's most probably the backlights switching off?.

    Are the backlights still ON when the pictures goes?.
     
  17. jamoo

    jamoo New Member

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    how can i buy LG electronics part online
     
  18. mneary

    mneary New Member

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    This thread is about a SHARP LCD.
     
  19. sdmtidor

    sdmtidor New Member

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    Hell0.......... Good day to all............
    i need help for my IBM thinkpad loptop v5.......
    auto shot off.... need schematic diagram for the main board.........
     
  20. unclejed613

    unclejed613 Well-Known Member

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    how many ways can we hijack a thread????????? read carefully...
    S-H-A-R-P L-C-D T-V

    if you still have a dark. but visible (under bright light) picture, it's the inverter board.
     
  21. MikeM

    MikeM New Member

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    Same Boat

    Hi Guys - first post, please be gentle.

    Yetiman,

    I have a Sharp LC37HV4E in for service which wouldn't come on until service mode was used. The menu stated error code 5 which I cleared. At the moment it's coming on from cold but I doubt very much that it's the cure.
    Did you end up changing the opto's and did it cure your problem?
    I too do not have a schematic, so may be in need of one.

    Many thanks in advance,

    MikeM
     

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