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    Samsung 2494HM repair

    Hi all,

    A few weeks ago I bought a defective Samsung 2494HM, last weekend I managed to fix it. I have used it every night this week without any problem whatsoever. Looks like a confirmed definitive repair! Anyway, here's the story.

    This monitor had developed the '2 sceond to black' problem. I suspected bad caps, but after opening they looked fine. The CCFL's proved to be OK when testing on a known good PSU. The fault turned out to be in the inverter transformer, a TM10176. This one has 1 primary and 2 secondary windings in one housing. The secondaries showed a big difference in resistance, one was about 1000 Ohm (as it should be), the other more than 3000 Ohm.

    Searching on the net I found a replacement in an Ebay webshop, cost just shy of US$6 (excl. Paypal cost, that is). Ordered it (free shipping) and received it in the mail after only 2 weeks. It looks identical to the original one, good build quality judging by outward appearance.

    After swapping the transformers the monitor came right back to life and has run without a hitch since.

    Nice display BTW, has VGA, DVI and HDMI inputs, and even a small audio amp with 2 (equally small) loudspeakers.

    What amazes me, though, is that one of the secondaries developed a higher resistance. When malfunctioning you'd expect it to go infinite, not just to 3000 Ohm. I would anyway, but then again, I don't have an education in electronics. Maybe one of the experts could shed some light on this subject?

    re-atari
    Last edited by re-atari; 01-18-2014, 07:02 AM.

    #2
    Re: Samsung 2494HM repair

    Hello,
    I have this same monitor and the caps look "normal" as well.

    I don't exactly know which pins to measure for the inverter transformer.

    I see the inverter transformer and it looks like there is one row of 4 pins and then another row of 2 pins.

    On the row with the 4 pins - if I call them pin1, pin2, pin3, pin 4

    While still soldered in the board..

    The resistance between pin1 and pin2 is aobut 1kohms, the same for pin3 and pin4 measured against each other.

    The resistance between pin1 and pin 3 is about 192k, the same for pin2 and pin4 measured against each other.

    Did I do that right? Do those numbers look correct?

    Thanks,
    Matt

    Comment


      #3
      Re: Samsung 2494HM repair

      Originally posted by BadMatt View Post
      I don't exactly know which pins to measure for the inverter transformer.

      I see the inverter transformer and it looks like there is one row of 4 pins and then another row of 2 pins.

      On the row with the 4 pins - if I call them pin1, pin2, pin3, pin 4

      While still soldered in the board..

      The resistance between pin1 and pin2 is aobut 1kohms, the same for pin3 and pin4 measured against each other.

      The resistance between pin1 and pin 3 is about 192k, the same for pin2 and pin4 measured against each other.

      Did I do that right? Do those numbers look correct?
      If you have the Kilimanjaro PSU board, the secondary windings are on the 4 pins leading to backlight connectors CN301/CN302 and CN303/304. It's the ones on the transformer's side towards the side of the board, if I understand you correctly you indicated them as nrs. 1 to 4. You can measure the scondary windings with the transformer soldered in. Each should measure about 1K Ohm, so both appear to be OK on your transformer.

      That leaves several other culprits, such as the CCFL lamps, mosfets, caps. If you have access to another monitor, I'd start by swapping the backlight wiring, to see if the 2494's PSU can fire up the other monitor's lamps. And vice versa.
      BTW: do check if the wiring is still connected correctly to the 2494's lamps, if the solder connection gets loose on only 1 lamp the backlight will shut down as well.

      It only makes sense to start swapping caps or fets if your lamps are OK. Replacing the lamps is a real pain, they are quite expensive and break very easily. Not to mention you have to take the entire frontpanel assembly apart in order to get to them. Speaking from own experience (on another Samsung monitor)...

      re-atari
      Last edited by re-atari; 03-05-2014, 07:54 AM.

      Comment


        #4
        Re: Samsung 2494HM repair

        When wire is burnt, it may still make contact but very poor to each other so the resistance can show higher readings, as shown in my pictures. 1407 Ohm is the bad winding.
        http://s807.photobucket.com/user/bud...tml?sort=3&o=1
        http://s807.photobucket.com/user/bud...tml?sort=3&o=2
        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


          #5
          Re: Samsung 2494HM repair

          Well, I got the same monitor with the same problem - 2 seconds to black. I measured the transformer and it's 760 Ohm on one side and 1k Ohm on the other. Am I right to assume the transformer is bad?

          Comment


            #6
            Re: Samsung 2494HM repair

            Originally posted by Half-Saint View Post
            Well, I got the same monitor with the same problem - 2 seconds to black. I measured the transformer and it's 760 Ohm on one side and 1k Ohm on the other. Am I right to assume the transformer is bad?
            Yes.
            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


              #7
              Re: Samsung 2494HM repair

              Replaced the transformer and the monitor works. Cheers for helping :-)

              Comment


                #8
                Re: Samsung 2494HM repair

                Looks like I'm not done with this monitor. There are three other problems that I'm now noticing:

                1. There are a few bright dots in the lower left quarter of the screen which I removed temporarily using a suction cup on the backside of the panel. However, they came back in less than half an hour but are not as visible. I suspect these are dust particles which entered the panel along with some water when it was left out in the rain by the previous owner who dumped it.
                2. As long as brightness is set between roughly 60 and 90, there's this buzzing sound coming from the PSU. What could it be?
                3. Occasionally the brightness will vary similar to someone changing the brightness values very fast then it goes back to where it was. This effect can last up to 3-4 seconds. The caps look fine but I haven't got an ESR meter so can't really check.
                Last edited by Half-Saint; 07-20-2016, 02:47 AM.

                Comment


                  #9
                  Re: Samsung 2494HM repair

                  Hi,
                  I also got the same monitor that has the 2 seconds to black issue. I measured all the caps and the ESR is in splso cec. I checked the transformer secondaries and they are both spot on (1.04K ohm).

                  So I next suspected bad CCFLs. Sure enough, monitor ran fine after the first one I disconnected, and substituted with my test CCFL from a 14 inch laptop. However, later I found out that it does not matter which one I CCFL I disconnect and replace with the one from laptop.

                  So, the monitor would ran fine with any of the 4 original CCFLs as long as the one of these four is substituted with a different CCFL. And it doesn't matter which one I substitute.

                  Any thoughts on this? Thanks
                  Last edited by mitchw; 01-07-2018, 06:32 PM.

                  Comment

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