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    Samsung Syncmaster T240 Backlight/Inverter Failure

    Hello,

    My Samsung monitor died a few months back and not being covered under warranty I decided to try and fix it.

    The Problem:

    I left my room and came back to find my monitor display blank. Upon closer examination I can barely see a display and only when I view it at an angle with a light. I unplugged the monitor and plugged it back in but no change or flickering of the display. After some research I concluded that the back lights were not functioning.

    I disassembled the monitor (what a horribly tedious job that was!) and inspected the power supply and CCFLs. I could not see any obvious signs of 'bad caps', burnt fuses, loose soldering joints, but I did notice all 4 CCFLs were black at each end.

    Long story short, I ordered new CCFLs under the assumption they had burnt out and replaced the old ones, a process which I never want to do again! The new CCFLs did not fix the problem and I am still experiencing a very dim display.

    Now this leaves me with a few suspects that are causing the problem and before I spend any more money I need you guys to give me some input:

    1) My soldering of the CCFLs to the old harnesses in some way was not sufficient to run the lamps or it damaged the replacements. I was VERY VERY careful with this process in regards to heating the connections.

    2) There is a bad cap on the power supply. Although each capacitor clearly has no bulging or leaking that is visible, is this still a possibility?

    3) After reading several threads on this subject I noticed that it is common for the CCFLs to light up for a few seconds before the inverter shuts off. In my situation, the lights remain off. Does this hint at the culprit?

    I would greatly appreciate any help with this issue as my only option I have now would be to replace the power supply board completely at a cost of nearly 100$!

    Please refer to this thread for pictures and capacitor info.

    Thank you!

    #2
    Re: Samsung Syncmaster T240 Backlight/Inverter Failure

    Have you checked F301?
    Al.
    Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

    Comment


      #3
      Re: Samsung Syncmaster T240 Backlight/Inverter Failure

      Originally posted by Funkhauser View Post
      2) There is a bad cap on the power supply. Although each capacitor clearly has no bulging or leaking that is visible, is this still a possibility?
      Yes. A bad capacitor would not give power to the inverter section of the board to light up the ccfl.

      3)In my situation, the lights remain off. Does this hint at the culprit?
      Yes, you could have a shorted transistor or open fuse in the inverter section which would cause the ccfls to remain off.

      You will need a multimeter to perform the above tests.

      Please refer to this thread for pictures and capacitor info.
      I'm not blaming you, but it seems like in the last 10 days or so, new members are becoming lazy in not posting pictures of their boards.

      Most say it is similar to this pic in post xyz. Similar and identical are NOT the same. Even the smallest nuance/change gives us a clue as to what is wrong with your specific board.

      Imagine going to a surgeon with someone else's x-ray. Would you want that surgeon to operate on you because the x-rays are similar?

      So post a picture of your board using managed attachments.
      --- begin sig file ---

      If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

      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.

      Please do not post inline and offsite as they slow down the loading of pages.

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      Comment


        #4
        Re: Samsung Syncmaster T240 Backlight/Inverter Failure

        Yea I actually just checked and the fuse is working.

        Comment


          #5
          Re: Samsung Syncmaster T240 Backlight/Inverter Failure

          Well I did not want to post any pictures because my camera is not the best but if you think it will help.

          In the second photo there is what appears to be heat damage near the transformer and large R301 resistor.
          Attached Files

          Comment


            #6
            Re: Samsung Syncmaster T240 Backlight/Inverter Failure

            On the wiring harness (lower right on your photo) check for the output voltages, especially the 12-15V output. The 5V sounds like it's working because of the image you're seeing. The 12-15V ouput is what drives the inverter section. The legend for each wire is either stamped on the top and/or the bottom of the board.

            Comment


              #7
              Re: Samsung Syncmaster T240 Backlight/Inverter Failure

              I checked and it gave me 14.31 V and some nice sparks. To check the transistor, do I need to remove it from the board?

              Comment


                #8
                Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                Originally posted by Funkhauser View Post
                I checked and it gave me 14.31 V and some nice sparks. To check the transistor, do I need to remove it from the board?
                Hopefully, the sparking didn't cause any permanent damage. The heatsink with the two "transistors" on it are actually diodes (marked Dxxx, right?) that output the 5V and 14V. The transistor(s) that retiredcaps was talking about are probably surface mounted devices on the bottom of the board. And without better photos, it's really going to very difficult to go onward.

                Comment


                  #9
                  Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                  There is one transistor attached to a heatsink in the bottom left of my photo.

                  This website offers a better photo than what I can provide. It is the same board as far as I can determine.

                  Comment


                    #10
                    Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                    When you say the fuse is working, Does that mean 14v coming in and going out?
                    Al.
                    Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                    Comment


                      #11
                      Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                      I used the diode function on my DMM to check for continuity of the fuse. It beeped so I was satisfied.

                      Comment


                        #12
                        Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                        Is 14v getting to the fuse and getting out? no sparks this time
                        Al.
                        Last edited by alexanna; 11-10-2010, 03:53 PM.
                        Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                        Comment


                          #13
                          Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                          I checked from the ground to the anode and cathode of the fuse and it gave me 15 V for both and no sparks. I'm really wondering why I got sparks in the first place...Crappy meter?

                          I also checked the output for the CCFLs which registered 0 v (big suprise). So, the problem exists between the fuse and the outputs.

                          Comment


                            #14
                            Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                            I probably will not be able to help very far on this one, But on th 14pin connector what are the voltages of the pins marked on off and adj dim as you power on and off the monitor?
                            To get the sparks you did I am guessing your DMM lead bridged a ground and power pin.
                            Al.
                            Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                            Comment


                              #15
                              Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                              I checked the pins and according to my meter there was no voltage change. Just a constant 0 V. I measured for DC and AC just to be certain.

                              For testing purposes I have the power supply isolated from the rest of the monitor. Will this affect anything?

                              Thank you for the help so far, anything is appreciated!

                              Comment


                                #16
                                Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                                As far as the sparks go, Did you bridge a power and ground pin?
                                To test the on off and adj dim everything needs to be hooked up including a video source.
                                Al.
                                You will be measuring DC volts,The 30 pin ribbon cable to the LCD dose not have to be hooked up just make sure it's insulated
                                Last edited by alexanna; 11-10-2010, 05:26 PM.
                                Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                                Comment


                                  #17
                                  Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                                  Ok. For the measurement I had the negative lead of the DMM on the test/ground.
                                  Yes, I believe I did bridge the ground.

                                  For the adj dim pin, it changes from 0.8v to -4.31v when switched from off to on.

                                  For the on/off pin I got some weird values. It stays at -0.5V but when switched off to on, it jumps to 1.5 or 2.0 V then to -4.3V and then to 0V. After a few seconds it switches back to -0.5V. It was hard to determine the values as they seemed to change too fast for my crappy meter.

                                  I hope this helps!

                                  Comment


                                    #18
                                    Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                                    Something is not making sense to me.
                                    Could you recheck all of the voltages on the 14 pin connector, use a plated screw hole for the ground of the DMM
                                    Al.
                                    Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                                    Comment


                                      #19
                                      Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                                      Ok. Your instincts were correct.
                                      The adj dim is 0.8V on and 0 V off.
                                      The on/off is 4.6V on and 0V off. However, if I switch the monitor off and on with the DMM lead attached to the pin it reads 0V. I can only get the 4.6V when I switch the monitor on and then read the pin voltage.

                                      Comment


                                        #20
                                        Re: Samsung Syncmaster T240 Backlight/Inverter Failure

                                        On the backside of the power board, there is a chip marked U201. What is the part number of that chip?

                                        Then look for its datasheet. The datasheet will tell you which pins are VIN, GND, etc. See if the 15V DC gets to that chip.
                                        --- begin sig file ---

                                        If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                                        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.

                                        Please do not post inline and offsite as they slow down the loading of pages.

                                        --- end sig file ---

                                        Comment

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