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LG 42LF65 LCD (No picture - Sound ok)

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    #1

    LG 42LF65 LCD (No picture - Sound ok)

    first off, let me say thanks for the help i received yesterday with the philips 50pf7521d plasma, sound amp card was 15 british pounds

    now i have a 42" Lg LCD TV. model number 42lf65.

    powers on fine, can hear sound, no picture, no backlight.

    psu has 1 dodgy capacitor 3300uf 10v, its got i little blacky brown mark on top.

    2 inverters, one either side, they seem to be hidden with the lcd, i havn't seen that before.

    I just been to maplin, to buy capacitors, they dont stock 3300uf any voltage.

    so whats the odds on replacing the cap and this tv bursting to life again, i think there slim. i think it could be main board problem.

    anybody have any ideas?

    also are these inverters replacable? if they are even faulty?
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    #2
    Re: LG 42LF65 LCD (No picture - Sound ok)

    update: if i hold a torch at front of screen, i can see the picture very faintly.

    so it looks like the inverters are not turnig on?

    now im thinking, its either:
    1. psu not turning inverters on (maybe due to 1 or more bad caps)
    2. main board not telling psu to turn inverters on.
    3. inverters are faulty

    is there any more tests i can do before i order parts, only to find that that part isnt faulty?

    thanks

    Comment

      #3
      Re: LG 42LF65 LCD (No picture - Sound ok)

      There are no separate inverters the power supply outputs voltage to run the ccfls. Most likely a bad inverter section on the power supply. I had the same problem on a Philips and a new power supply fixed it.

      Comment

        #4
        Re: LG 42LF65 LCD (No picture - Sound ok)

        thanks rayrod81, is the a ceratin component on the inverter section that goes? do you think that cap thats leaked a bit would cause that?

        i never seen an inverter like that, had a feeling it could be built in.

        i think i can get a psu for around 50 uk pounds, im just hoping i have not got anymore problems elsewhere, theres nothing worse than ordering a part, fitting to find its the same.

        plain bill may have an idea, thanks again rayrod81

        Comment

          #5
          Re: LG 42LF65 LCD (No picture - Sound ok)

          On the Philips there were bad SMD diodes on the back of the board and bad mosfets on the inverter section. There was a bad cap on the secondary side on the Philips that kept the TV from turning on at all. After I replaced it the TV turned on but had no backlights. It couldn't hurt to replace the cap and see if that fixes it cause it would be a cheap experiment. The fact that your TV turns on and works fine but has no backlights pretty much takes the main board and T-con out of the equation. That leaves the power supply as the prime suspect.
          Last edited by rayrod81; 07-01-2011, 11:28 AM.

          Comment

            #6
            Re: LG 42LF65 LCD (No picture - Sound ok)

            It would be useful to see pictures of the inverters. LG has produced a number of dodgy master-slave inverters that are failing.

            PlainBill
            Last edited by PlainBill; 07-01-2011, 01:16 PM.
            For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

            Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

            Comment

              #7
              Re: LG 42LF65 LCD (No picture - Sound ok)

              hi plain bill. where are the inverters? theres 2 single wires, both goin from psu to either side of the lcd, it doesnt even look like the inverters are seperate but i might be wrong, i cant see how they come out??

              Comment

                #8
                Re: LG 42LF65 LCD (No picture - Sound ok)

                That PSU has bulging caps in it, I'd replace the circled ones first.....
                Attached Files
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                Corsair AX1200

                Comment

                  #9
                  Re: LG 42LF65 LCD (No picture - Sound ok)

                  so thats:

                  1 x 2200uf 10v
                  1 x 3300uf 10v

                  went to maplin in uk today, no luck.

                  im going to google.

                  Thank you, i will keep you informed.

                  Comment

                    #10
                    Re: LG 42LF65 LCD (No picture - Sound ok)

                    I strongly suggest that you change all eight of the caps in that section. There is no way that I'd not suspect the remaining caps after I found two bulging. If you cannot find what you need nearby, order them from either here badcaps.com or digikey.
                    The strong-minded rise to the challenge of their goals,the weak-minded BECOME HATERS

                    Comment

                      #11
                      Re: LG 42LF65 LCD (No picture - Sound ok)

                      This panel is a newer panel that does not have inverters. Many of the newer LG Panels have the inverter contained on the Power Supply.

                      Comment

                        #12
                        Re: LG 42LF65 LCD (No picture - Sound ok)

                        right i found the 2 caps i needed in my glory cupboard. replaced the 2. still the same problem.

                        im debating whether to just pick up another power supply tomorrow. 30 mile trip to bolton, thats when i get home test it and still same problem. fingers crossed.

                        Comment

                          #13
                          Re: LG 42LF65 LCD (No picture - Sound ok)

                          just tested tv again. seen a little flash under where the inverter usually is.

                          i instantly turned it off again.

                          also when i seen the flash, there was sound like electric shorting.

                          i hope ccfls havn't shorted and its just a sign that the inverter part of psu is faulty.

                          im

                          Comment

                            #14
                            Re: LG 42LF65 LCD (No picture - Sound ok)

                            I have the same issue. No back light. I can see faint picture with flash light. But I have two slave inverter left and right. Is there any way to test the inverter? Anybody can tell me if I have bad inverter or faulty power supply?


                            I am getting 24v from power supply for inverter. But I am getting only 1.9V output for main board where it should be 3.4 volts ON.


                            Is is possible that this low voltage stopping the inverter from turning on?
                            Attached Files
                            Last edited by arman960; 09-16-2012, 05:57 PM.

                            Comment

                              #15
                              Re: LG 42LF65 LCD (No picture - Sound ok)

                              If your sound is ok and also since you do have a picture without the backlights, I would mostly suspect that the master inverter is good but the slave is probably the problem. Usually, you won't get any picture at all with a bad master. I could be wrong though.

                              Take the coverings off of the master and slave inverters and post pictures of the boards. There should be four mosfets that need checked on each board.
                              The strong-minded rise to the challenge of their goals,the weak-minded BECOME HATERS

                              Comment

                                #16
                                Re: LG 42LF65 LCD (No picture - Sound ok)

                                Check the fuses on the inverter boards, read this thread:
                                https://www.badcaps.net/forum/showth...729#post266729
                                Never stop learning
                                Basic LCD TV and Monitor troubleshooting guides.
                                http://www.badcaps.net/forum/showthr...956#post305956

                                Voltage Regulator (LDO) testing:
                                http://www.badcaps.net/forum/showthr...999#post300999

                                Inverter testing using old CFL:
                                http://www.badcaps.net/forum/showthr...er+testing+cfl

                                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                http://s807.photobucket.com/user/budm/library/

                                TV Factory reset codes listing:
                                http://www.badcaps.net/forum/showthread.php?t=24809

                                Comment

                                  #17
                                  Re: LG 42LF65 LCD (No picture - Sound ok)

                                  This is exactly why multiple cross postings piss me off. It creates extra work for all the regulars.
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                                  We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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                                  Comment

                                    #18
                                    Re: LG 42LF65 LCD (No picture - Sound ok)

                                    I have this TV (LG 42LF65), whenever I turn it on it takes anything from 20-60 minutes before it comes on and goes into standby. Upon pressing standby (red light) it then powers itself off for a few minutes and eventually comes on (green light) after repeating this process a few times.

                                    It also takes a few goes before I have sound as well, all I hear the first few times is loud crackling and random noises.

                                    Any ideas as to what the problem may be or it is a lost cause?

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