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Samsung 2433BW: 2 seconds til black

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    Samsung 2433BW: 2 seconds til black

    I have exhausted the resources here and elsewhere to the best of my ability.
    Observations, then what I've tried:
    Observations:
    1) There are 4 CCFL's attached via two connectors: CN301 & CN304. It doesn't matter which CCFL cable is plugged into CN304: That cable's lamps illuminate and stay lit indefinitely just fine, provided there's no video input. It doesn't matter which CCFL cable is plugged into CN301: That cable's lamps never illuminate, with or without video input.
    2) Without video input, the lamps on whichever CCFL connector is attached to CN304 are lit fine, and the "No Video Signal" graphic floats around the LCD. Upon applying video signal input, all lamps go dark in 2 seconds.
    3) Without video input, there's 15VDC relative to chassis ground on both leads of F301 (power input to the inverter). Two seconds after video signal is applied, this increases to 21VDC.
    4) Inverter transformer T301 has 8 pins with in-circuit resistance readings as follows: (I have pin #'s in red on the foil side photo)
    Pin 1 to 2: 0 ohms
    Pin 2 to 3: about 0.2 ohms, both meter lead polarities
    Pin 3 to 4: 500 ohms in one direction; about 6K-ohms with cap charging behavior in the other meter lead polarity.
    Pin 5 to 6: 1050 ohms (this goes to CN304)
    Pin 7 to 8: 980 ohms (this goes to CN301, the CCFL port that's always dead)
    5) This board doesn't appear to have any V sense capacitors. There's no evidence anything was ever soldered into C303 or C304. An identical board #LS24CMKKFVC listed on eBay also doesn't have these cap's.
    6) This board appears to only have load capacitors at CN301 (C301 & C302).
    7) There is very mild darkening of the board next to T301, so I guess the transformer runs warm, but I see this a lot even in working units.
    8) There is no sign elsewhere of any thermal issue or suspect solder connections.

    What I've done:
    I've replaced every electrolytic capacitor on the board except for the tiny C111 which appears to be associated with the user control button input connector. I used all new Nichicon 105°C capacitors from DigiKey of the exact capacitance & voltage rating as the originals, some of which were "Sam Young" brand, but none of these showed any signs of bulging or leakage. Absolutely zero change in the above symptoms, observations and readings after doing this.

    Ideas?
    Attached Files

    #2
    Re: Samsung 2433BW: 2 seconds til black

    I have seen a lot of inverter transformers which can work if the secondary resistance varies by as much as 10% between the two windings,and some where a lot less stops them,and the Forum in a lot of places say 3%-5% max..based on that I would change the transformer

    Comment


      #3
      Re: Samsung 2433BW: 2 seconds til black

      I've never experienced a bad HV transformer on an inverter board. Rtech may be right.

      Another thing to look at is the small value ceramic capacitors that are near the HV outputs. C301 and C302. These caps can go bad. They may appear discolored. They could be shorted, or they start to leak when high voltage is applied. They look good in the photo, but it might be worth replacing them. Its probably cheaper and easier to replace a couple caps than the transformer.

      It looks like C301/C302 are connected in parallel with the CN301 output (often, these are series capacitors). And you report CN301 is always dead. Its hard to see from the photos how everything is connected. Try tracing out a schematic on this part of the board; transformer secondaries, capacitors to CCFL bulbs and returns.

      Comment


        #4
        Re: Samsung 2433BW: 2 seconds til black

        Victory. Like Ken256, I've never experienced a bad HV transformer on an inverter board, until now. I got a replacement on eBay and was encouraged right away: both secondary windings measured 1050 ohms on the new xformer, while one winding on the original xformer was 1050 ohms, and the other measured 980 ohms, both measured out-of-circuit. I put the new transformer in, and voila: up & running great. Thanks to Rtech for the suggestion.

        Comment


          #5
          Re: Samsung 2433BW: 2 seconds til black

          Great job and thanks for the repair feedback.
          Never stop learning
          Basic LCD TV and Monitor troubleshooting guides.
          http://www.badcaps.net/forum/showthr...956#post305956

          Voltage Regulator (LDO) testing:
          http://www.badcaps.net/forum/showthr...999#post300999

          Inverter testing using old CFL:
          http://www.badcaps.net/forum/showthr...er+testing+cfl

          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
          http://s807.photobucket.com/user/budm/library/

          TV Factory reset codes listing:
          http://www.badcaps.net/forum/showthread.php?t=24809

          Comment


            #6
            Re: Samsung 2433BW: 2 seconds til black

            Well done.

            Comment


              #7
              Re: Samsung 2433BW: 2 seconds til black

              Thanks guys!
              I had the exact same issues with my 2443BW and was fixed by swapping the HV transformer. For reference, the resistance on mine was 1044 and 997 which about 5%

              Comment


                #8
                Re: Samsung 2433BW: 2 seconds til black

                Adding a 2443BW variant, "2 sec to black with input signal present"

                - Monitor would toggle between dim Analog & Digital no signal present icons all day, yet go dark 2 sec after a signal was applied to analog or digital inputs.
                - Determined the top lamp output would not fully light a spare lamp with either top or bottom internal lamps connected. Under this test the Analog & Digital icons were visible at the same dim level so both internal lamps appeared to be working.
                - Removed the transformer, measured 885 ohm / 1050 ohm top / bottom lamp output winding resistances. Also observed 2 of six top winding groups were discolored yellow.
                - Ordered PN TM-09176 transformer from JK_PARTS on EBAY which arrived in 2 weeks as opposed to the initial estimate of 6 weeks
                - Installed the new transformer and problem solved.
                - Replaced all electrolytic caps except the main rectifier cap while in the neighborhood...

                Yet another monitor saved from the recycler thanks to the amazing Badcaps.net community!

                Comment

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