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    #1

    LG 1718S-BN no video

    I'm trying to repair a LG LCD 1718S which has the followiong symptoms.

    When you power it on the green light comes on so there is power to the board. 9 out of 10 times when you power it on you get the 2 seconds to death syndrome. Only its more like 0.5 seconds. The other time the picture is visible but disappears 10 seconds later. When it goes black however if I shine a torch on the LCD I dont see the pic. I've also had a look for bulging caps and all the caps look perfect (except for the ones covered in the white paste - can't see the tops) so I'm not sure if its a cap problem - could it be?

    Should I just blindly replace the caps and hope for the best?
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    #2
    Re: LG 1718S-BN no video

    Try referring to retiredcaps "2 seconds to black" guide starting at post #13.

    https://www.badcaps.net/forum/showth...ck+retiredcaps

    Eventhough you have no the image after you shine the flashlight, it still makes for good reading.


    Also, after the panel goes dark, does the power light still stay green?
    Last edited by jetadm123; 12-06-2010, 11:26 AM.

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      #3
      Re: LG 1718S-BN no video

      Originally posted by gregmcc View Post
      Should I just blindly replace the caps and hope for the best?
      You can scrape off the glue and check the caps. The glue is used during manufacturing to hold components in place. I would hold off replacing the caps until I exhausted all other possibilities.

      I marked what I believe are the secondaries. Put your multimeter on 2000 ohm (if manual). With power off and LCD unplugged, measure the resistance between the red dots. Do the same for blue. Report both readings.

      Do you have a spare LCD monitor lying around?
      Attached Files
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        #4
        Re: LG 1718S-BN no video

        Originally posted by retiredcaps View Post
        You can scrape off the glue and check the caps. The glue is used during manufacturing to hold components in place. I would hold off replacing the caps until I exhausted all other possibilities.

        I marked what I believe are the secondaries. Put your multimeter on 2000 ohm (if manual). With power off and LCD unplugged, measure the resistance between the red dots. Do the same for blue. Report both readings.

        Do you have a spare LCD monitor lying around?
        I've scraped off the glue - all looks fine.

        Measured both points - they measure 460R.

        Funnily enough I have another LG (slightly bigger - 22") which is in pieces as I'm waiting for low ESR caps to arrive for it.

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          #5
          Re: LG 1718S-BN no video

          Originally posted by gregmcc View Post
          Funnily enough I have another LG (slightly bigger - 22") which is in pieces as I'm waiting for low ESR caps to arrive for it.
          The reason for asking is to use another LCD "good ccfl" as a test. I'm not sure if the 17 inch LG LCD can drive a 22 inch ccfl properly.

          You can try, but no guarantees that it will help find a bad ccfl on the LG or not.
          Last edited by retiredcaps; 12-06-2010, 02:26 PM.
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            #6
            Re: LG 1718S-BN no video

            Originally posted by gregmcc View Post
            When it goes black however if I shine a torch on the LCD I dont see the pic.

            When it does go black, does the power light also turn off?

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              #7
              Re: LG 1718S-BN no video

              i'll give it a bash and try the other lcd.

              Nope -the green light stays on all the time.

              Comment

                #8
                Re: LG 1718S-BN no video

                Originally posted by gregmcc View Post
                i'll give it a bash and try the other lcd.
                You don't have to remove the ccfls from the other monitor. Just stretch the cables from the LG to one of the ccfls. Don't let the monitors touch each other.
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                  #9
                  Re: LG 1718S-BN no video

                  Originally posted by retiredcaps View Post
                  You don't have to remove the ccfls from the other monitor. Just stretch the cables from the LG to one of the ccfls. Don't let the monitors touch each other.
                  Ok - before I blow myself up I just want to clarify this.

                  The suspect monitor has 4 plugs going to the CCFL's on the screen. Your saying disconnect one of the them and plug a CCFL from another LCD its place? Can it be anyone or the connectors? There's no particular order is there? Do I just do one at a time?

                  I clearly don't understand the process as how can a CCFL in another LCD help - the picture will still be displayed on the suspect LCD correct?

                  I think I need to go and read up on CCFL's before I attempt this

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                    #10
                    Re: LG 1718S-BN no video

                    Originally posted by gregmcc View Post
                    Ok - before I blow myself up I just want to clarify this.
                    I use a power bar for these tests and flick the switch on/off.

                    The suspect monitor has 4 plugs going to the CCFL's on the screen.
                    Yes.

                    Your saying disconnect one of the them and plug a CCFL from another LCD its place? Can it be anyone or the connectors? There's no particular order is there? Do I just do one at a time?
                    Yes one at a time. This is described in detail in section #5.

                    I clearly don't understand the process as how can a CCFL in another LCD help - the picture will still be displayed on the suspect LCD correct?

                    I think I need to go and read up on CCFL's before I attempt this
                    Yes, the picture will be displayed on the suspect LCD.

                    My explanation of how this works is not technical, but the inverter controller chip is an "all or nothing". If all the ccfls are within specifications, the backlights will all come on. If even one ccfl is bad, then the all backlights are turned off.

                    What we are trying to do is figure out which ccfl is causing the 2 seconds to black. So by using a "good" ccfl from another monitor, we can do process of elimination.
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                      #11
                      Re: LG 1718S-BN no video

                      Originally posted by gregmcc View Post
                      I clearly don't understand the process as how can a CCFL in another LCD help - the picture will still be displayed on the suspect LCD correct?
                      Maybe this analogy will help?

                      You have a 4 AA cell flashlight. It does not work. You have a spare AA battery. You have no multimeter.

                      Assuming only one AA battery in your flashlight is bad, how would you figure out the bad one?

                      I would substitute one AA out of the time with the spare and retest to see if the flashlight works or not.
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                        #12
                        Re: LG 1718S-BN no video

                        Ahh - thanks for the explanation. Makes sense.

                        Getting somewhere now. By plugging in 3 ccfl's and using one from a good LCD I found one of them is giving the problem.
                        With No 2,3,4 and one connected from another LCD the picture displays perfectly.

                        I guess it means no. 1 is shot. Is it worth trying to source another ccfl or is the monitor ready for the dump?

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                          #13
                          Re: LG 1718S-BN no video

                          Originally posted by gregmcc View Post
                          I guess it means no. 1 is shot. Is it worth trying to source another ccfl or is the monitor ready for the dump?
                          Yes, it is worth trying to fix. Note this is the 4th or 5th similar problem in the last 7 days.

                          Your problem may NOT be the actual ccfl, but the wiring. See pics to help you narrow down the problem.

                          http://s807.photobucket.com/albums/y...klight%20lamp/

                          PS. Most cities have a recycle center or you can give it away for free on craigslist versus the dump.
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                            #14
                            Re: LG 1718S-BN no video

                            PS. Taking apart the ccfl is very delicate work and a few people here have broken them. This gives you an idea of the work involved.

                            http://ccflwarehouse.com/lasotu.html
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                              #15
                              Re: LG 1718S-BN no video

                              I see what you mean about delicate work
                              I got it opened up and one of the ends of the CCFL is blackened.
                              Attached Files

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                                #16
                                Re: LG 1718S-BN no video

                                Originally posted by gregmcc View Post
                                I got it opened up and one of the ends of the CCFL is blackened.
                                You can buy bare, pre-wired, or pre-housed ccfls from ccflwarehouse.com. Bare is the cheapest, but the hardest to put back together and install.

                                ccflwarehouse.com has good feedback from members here.

                                It is your call whether it is worth repairing from a $$$ point of view now that we know it is not wiring (which would have just required re-soldering).
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                                  #17
                                  Re: LG 1718S-BN no video

                                  Thanks for the help. At least I know what the problem is.

                                  Don't think it will be worth repairing. The lamps I will have to get via international shipping which will work out expensive and it doesn't look too easy. They look really easy to break which will take me back to step 1.

                                  Will see if I can donate the parts to someone locally and buy a new monitor. Or maybe keep a working ccfl for any future lcd repairs/testing

                                  Again thanks for the help.

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                                    #18
                                    Re: LG 1718S-BN no video

                                    Originally posted by gregmcc View Post
                                    Don't think it will be worth repairing. The lamps I will have to get via international shipping which will work out expensive and it doesn't look too easy. They look really easy to break which will take me back to step 1.
                                    Have a look at ebay. Here is one 17 inch ccfl. It is for a Samsung, but many of these are interchangeable. Only $6.50USD with free shipping (at least to Canada).

                                    http://cgi.ebay.com/17-LCD-CCFL-LAMP...item43a3466969

                                    Measure the dimensions of your ccfl and ask seller for dimensions in the auction.
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