Sceptre X20G - testing ccfl bulbs

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  • Welchs101
    Badcaps Veteran
    • Sep 2008
    • 979
    • USA

    #1

    Sceptre X20G - testing ccfl bulbs

    Hi,

    I am trying to repair a sceptre x20g naga iii lcd monitor. I am testing the ccfl bulbs using another monitor as the power source.

    Note: To test bulbs what i do is take another known good monitor. Disconnect one of the wires going to one of the ccfl lamps. I take the voltage coming from the "good" monitor and instead of running it to the good ccfl lamps i run it to the ccfl lamps i am trying to test. What i look for once i turn on the known good monitor is if the "no video connection" dialog box stays on the screen. If it does the lamp is good.....if it does not the lamp is bad.


    Ok, so i opened up the Sceptre X20G and there are 6 wires going to the ccfl lamps (see enclosed pic). Before i opened it up......and this may be important ......screen appears as if the lamps come on for a few seconds....sometimes a little longer. Picture looks good. So i know that at least some of the bulbs are working.

    I think on an earlier post i red that the "larger" diamter wire is the hot and smaller diameter wire is not the hot. Ok, from the pic you can see that the connector with the "white and white" has a larger and smaller diameter wire. So when i test this..........i get that the lamp is ok. When i move on to the other wires i get an interesting result.

    In the other connector there are "pink-lightblue" and "black-darkerblue". I hope no one is color blind. Ok....when i test the pink-lightblue combination i put the "hot" wire to the "pink" and the "not-hot" to the "lightblue". The "no video connection" dialog box only comes on for a second. This tells me the lamp is bad. I did the same thing for the "black-darkerblue" with the hot going to the darkerblue. Same result......bad. The problem is that i am not sure i believe it.

    When i test the top bulbs i get the same exact response. The white-white, good, the pink-lightblue bad, black-darkerblue bad. So i am thinking that i am measuring the white-white connection ok on the top and bottom bulbs but when i measure the "pink-lightblue" and "black-darkerblue" bulbs perhaps i am doing something wrong.

    I am having a hard time believing that 4 ccfl bulbs are bad when i initially got a good picture for several seconds. And the bulbs that are bad are the ones in the 5-pin connector.........i have this feeling that i am either measuring wrong or making a wrong assumption.

    I hope i have not confused anyone.........does anyone have any suggestions or thoughts?
    Attached Files
  • Welchs101
    Badcaps Veteran
    • Sep 2008
    • 979
    • USA

    #2
    Re: Sceptre X20G - testing ccfl bulbs

    One more thing..........the "pink-lightblue" and "black-darkerblue" wires are all the same size. So i am not sure which one is the hot.

    Comment

    • Welchs101
      Badcaps Veteran
      • Sep 2008
      • 979
      • USA

      #3
      Re: Sceptre X20G - testing ccfl bulbs

      I am enclosing pics of front and back of board. Perhaps you can tell something from this pic. Like which ones are supposed to be hot and/or anything else.
      Attached Files

      Comment

      • Welchs101
        Badcaps Veteran
        • Sep 2008
        • 979
        • USA

        #4
        Re: Sceptre X20G - testing ccfl bulbs

        ok...i am enclosing a pic for further clarrification.

        Ok....i had assumed (and i think it was wrong to do so) that wires 3/4 and wires 5/6 were "together". What i mean by "together" is that for example wire 3 and 4 make up the connection for one of the ccfl tubes. However, i am thinking that really 3 and 4 are the "hot" wires and that "5 and 6" are the "non-hot wires".

        So i need to verify which wires are "hot". Then i need to verify which wires go with each other.

        Can someone help?

        I think wires 1, 3, and 4 are the "hot" wires".
        Wires 1 and 2 are "together"

        But i am not sure about wires 3, 4, 5, and 6.
        Attached Files

        Comment

        • PlainBill
          Badcaps Legend
          • Feb 2009
          • 7034
          • USA

          #5
          Re: Sceptre X20G - testing ccfl bulbs

          Arghh!!!!

          It's simple. The connector pins that have the white goop on the back of the board are the hot pins. The ones that don't are the return pins.

          The safe way to test this is to jumper both return lines from the monitor under test together, and hook that to the return line on the driving monitor. Hook one 'hot' line to the hot pin on the driving monitor.

          The quick way to match the hot line to the return line is to hook the hot line to the driving monitor, then (with the backlights on) stick a pin into either return connector. If you don't get a shock, that was the return line for the OTHER CCFL. (I don't recommend this procedure.)

          PlainBill
          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

          • Welchs101
            Badcaps Veteran
            • Sep 2008
            • 979
            • USA

            #6
            Re: Sceptre X20G - testing ccfl bulbs

            Hi Bill,

            Thanks! I really appreciate the info. I was thinking the two "hot" pins were grouped together.

            I wont hurt anything if i connect "hot" to one of the hot pins and then connect the other wire to one of the returns.......if i get the wrong return......it wont hurt anything will it? I am just trying to see if the lamp is ok.

            Comment

            • Welchs101
              Badcaps Veteran
              • Sep 2008
              • 979
              • USA

              #7
              Re: Sceptre X20G - testing ccfl bulbs

              Hey, just curious why do they put the "white goop" on the hot pins?

              Comment

              • PlainBill
                Badcaps Legend
                • Feb 2009
                • 7034
                • USA

                #8
                Re: Sceptre X20G - testing ccfl bulbs

                Originally posted by Welchs101
                Hey, just curious why do they put the "white goop" on the hot pins?
                Insulation, I assume. Electrical discharges tend to occur at points rather than smooth surfaces.

                And on your other question, no it won't hurt.

                PlainBill
                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

                • Welchs101
                  Badcaps Veteran
                  • Sep 2008
                  • 979
                  • USA

                  #9
                  Re: Sceptre X20G - testing ccfl bulbs

                  Thanks Bill.

                  Turns out one of the lamps is "bad". Thanks for the info!

                  Comment

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