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Samsung LCD Notorious "2 Seconds Black" faulty backlight

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    #1

    Samsung LCD Notorious "2 Seconds Black" faulty backlight

    Hi All

    Another project , this time another Samsung LCD Model: LE26R74BD

    This has the notorious 2 seconds black fault. The LCD Panel works , this was tested in dark with Torch
    Four bulging 1-MilliFarad Caps were replaced on the PSU ( Model BN9603833A) . The fault still resumed

    . Originally the backlight switched on for around half a second . This was improved to 2 seconds after swapping Inverter board

    I suspect either I have a faulty lamp CCFL or PSU component . Seemingly there are several compatible PSU for this TV ( BN96-03057A , BN96-03642A to name a few )

    Before swapping out the PSU or checking the lamps , it would be nice to hear your thoughts , suspicions, experiences and hunches with this issue

    I am fairly experienced with electronics and Meters , I just lack time to check everything at the moment
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    #2
    Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

    If you have swapped out the inverter board then I should examine the lamps.
    Have you any spare lamps you could use for test - perhaps build a test bulb
    see any post by Budm and in his signature there is a link on how to make one from a 14w cfl

    Please can you update your profile with country and mains voltage
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment

      #3
      Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

      Ok the CFL test is complete , the monitor still switches off , even with the CFL bulb attached. Every port was tested .

      Some other strange things I have noticed :
      When inserting Mains Voltage 240 V , there is a kind of very faint whistle sound which gets higher pitch after 3 seconds then stabilizes

      Upon switching on the TV, there is a brief second of 100% brightness , then a second of 40% brightness , then back-light stops .

      There is matching sounds , seemingly on when the screen dims there is a kind of slight arcing/buzzing sound which stops when backlight diminishes
      Seemingly there is a component dragging the voltage down , I may be wrong , just my suspicion .





      Using a flashlight , the settings menu can be accessed , all settings can be changed, apart from brightness , as soon as the brightness spectrum is changed , the user is thrown out of the menu !

      I am wondering if it is worth replacing the PSU , as they sell for around £20

      Again your thoughts are cherished

      Comment

        #4
        Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

        im leaning toward main av board on this one mate as you say the brightness option kicks you out of menu

        Comment

          #5
          Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

          Could be a possibility - try putting TV in standby then pressing info-menu-mute-power and selecting reset option.
          Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
          For service manual, schematic, boardview (board view), datasheet, cad - use our search.

          Comment

            #6
            Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight



            And In the Back of the Net

            'Good ol' Cowboy Heatgun trick and she is alive

            Wonder how long it'll last ........................

            Comment

              #7
              Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

              A bit more explanation of what you did might help others ? and me
              Like how hot how long for taped up? and so on.
              Please upload pictures using attachment function when ask for help on the repair
              http://www.badcaps.net/forum/showthread.php?t=39740

              Comment

                #8
                Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

                Originally posted by selldoor View Post
                A bit more explanation of what you did might help others ? and me
                Like how hot how long for taped up? and so on.
                well After changing the capaictors, I changed the Inverter board which done nothing really

                I then dusted all of the inside PCBA's using a paintbrush . I then proceeded to heat the PCBA's and components for around 2 minutes using a heat-gun , alternating between high and low heat , in a waving circulating fashion .I gave all components enough heat to make them hot to the touch . I waited a few minutes to col down , re-assembled and voila

                Comment

                  #9
                  Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

                  Ok - well done - thanks for that - be interesting to see how long it lasts.
                  Please upload pictures using attachment function when ask for help on the repair
                  http://www.badcaps.net/forum/showthread.php?t=39740

                  Comment

                    #10
                    Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

                    i just did one of these a quick flas of the backlights and that was it.....checked all fuses and a 3.15a near the top end of the board had blown and i measured the fets and the one in line with the fuse measured wrong changed it now all ok

                    Comment

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