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Samsung Syncmaster T240 - Bad Inverter Transformer?

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    #1

    Samsung Syncmaster T240 - Bad Inverter Transformer?

    My monitor has developed the 2 seconds to black fault. I've never tried to fix anything like this before but thought I'd give it a go just for the fun of it rather than pay someone else to do it and you guys make it sound really easy.

    I removed the power board from the monitor on from a quick visual inspection all appears well with the capacitors.

    Testing the secondary coils on the inverter transformer give reading of 952 and 918. I've read that 3 or 4% variance is enough to suggest a faulty transformer but mine seems to be borderline. Other threads I've read on here show much more dramatic differences in the coils, e.g. 950 and 600.

    So I'm wondering:
    1) In a new Inverter Transformer would both coils measure 950 or will there always be a bit of variance?

    2) Is the difference in mine enough to suggest a faulty component?
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    #2
    Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

    Originally posted by meths View Post
    So I'm wondering:
    1) In a new Inverter Transformer would both coils measure 950 or will there always be a bit of variance?

    2) Is the difference in mine enough to suggest a faulty component?
    Close enough for now until you rule out the lamps/wiring.

    2 seconds to black can be

    a) bad caps
    b) bad ccfls
    c) bad ccfl wiring (especially the return wiring)
    d) bad secondary windings on the inverter transformer

    More details starting with post #19 at

    https://www.badcaps.net/forum/showthread.php?t=10419

    Also, see budm's Inverter tester using old CFL

    https://www.badcaps.net/forum/showthread.php?t=19987
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      #3
      Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

      Thanks for the reply. I'll have a look at the CCFLs later but in the meantime here's a few pics of the board.
      Attached Files

      Comment

        #4
        Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

        Okay, so I've not got a spare CCFL to test with and I've not taken the panel apart to look at them so I did the following test:

        1) Plugged the bottom set of lights into the bottom connector (rightmost in the picture) and powered up. No image at all.

        2) Plugged the top set of lights into the bottom connector. No image at all.

        3) Plugged the top set of lights into the top connector. 2 seconds to black.

        4) Plugged the bottom set of lights into the top connector. 2 seconds to black.

        With my limited knowledge this suggests that it's likely that the CCFLs are fine as both gave exactly the same results and lit up in the top connector before going black. If one set was dodgy I'd have expected no light at all from it.

        When I noticed that the bottom connector didn't cause the lamps to light up at all I looked at the back of the pcb to try to see if there was anything up with it. It looks to me that power for this connector is routed through the secondary coil with lowest resistance (918) which seems to suggest that the inverter transformer is in fact the problem.

        So, what do you guys think? Have I solved the mystery?
        Attached Files

        Comment

          #5
          Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

          Originally posted by meths View Post
          It looks to me that power for this connector is routed through the secondary coil with lowest resistance (918) which seems to suggest that the inverter transformer is in fact the problem.

          So, what do you guys think? Have I solved the mystery?
          I can't tell from the picture, but try reflowing/resoldering all the joints regardless how they look in that section you highlighted in red.

          If that doesn't help, then the inverter transformer is the likely suspect.
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            #6
            Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

            A replacement is less than $4 USD + free shipping on ebay.

            http://www.ebay.com/sch/i.html?_from...-10160&_sop=15
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              #7
              Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

              I forgot to have you check those blue caps.

              With power off, measure the resistance of C301, C302 and C305. Also measure R302. Report all your readings.
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                #8
                Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

                I can't get a reading on C301 and C302. My meter only has up to 2M range and it's showing 1. for those two.

                C305 shows 931 ohms and R302 shows 149.7k ohms.

                Comment

                  #9
                  Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

                  Originally posted by meths View Post
                  I can't get a reading on C301 and C302. My meter only has up to 2M range and it's showing 1. for those two.

                  C305 shows 931 ohms and R302 shows 149.7k ohms.
                  Desolder C305 and remeasure the resistance. If it still reads 931 ohms, it is likely bad. These blue caps should read open circuit.

                  Even though the "top connector" works, you might as well measure those blue caps and verify they should read open circuit.

                  Check the color code of R302 and see if it matches your reading.
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                    #10
                    Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

                    So just to be clear, when the meter is showing 1 is that it reading open circuit?

                    I'll need to go and buy a soldering iron now I guess.

                    Comment

                      #11
                      Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

                      Originally posted by retiredcaps View Post
                      A replacement is less than $4 USD + free shipping on ebay.

                      http://www.ebay.com/sch/i.html?_from...-10160&_sop=15
                      I am inclined to agree with this course of action. However, i am not sure about the quickness of the shipping though.

                      Comment

                        #12
                        Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

                        Originally posted by meths View Post
                        So just to be clear, when the meter is showing 1 is that it reading open circuit?
                        "1" in the left hand side means out of range on a manual multimeter.
                        Last edited by retiredcaps; 03-11-2013, 07:36 PM. Reason: typo
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                          #13
                          Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

                          Thanks for all the help guys!!!

                          I ordered the inverter transformer from Hong Kong and bought a cheap 40w soldering set and I fixed the monitor tonight.

                          I've never soldered anything before and am quite pleased with my work - shiny joints and quite neat.

                          Now I need to go and find something else to solder...

                          Comment

                            #14
                            Re: Samsung Syncmaster T240 - Bad Inverter Transformer?

                            Originally posted by meths View Post
                            I ordered the inverter transformer from Hong Kong and bought a cheap 40w soldering set and I fixed the monitor tonight.
                            Good fix for $4.
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