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Lenovo ThinkVision L2440pwC stays black

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    #1

    Lenovo ThinkVision L2440pwC stays black

    Hallo!

    I am trying to repair a Lenovo ThinkVision L2440pwC, manufactured in September 2008.

    Problem

    The monitor worked flawlessly until last Friday, when in the morning it didn't light up.

    Now, when powering on the monitor, the display stays black (so it's not a "2secs to black" problem, it rather does not light up at all) and the power LED stays on. The picture is visible when shining light on it.

    Things tried

    I disassembled the monitor and looked for broken/burned/leaked parts and bad solder joints.

    Question

    The capacitors look good. Some solder joints don't. However I do not have a lot of experience with these things so I would like to ask you to have a look, too.

    As the picture quality of my camera is not that good, I took several detail pictures to capture all electronic parts on focused pictures.

    Thanks in advance for your advice!
    Attached Files
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    #2
    Re: Lenovo ThinkVision L2440pwC stays black

    Q107 and Q108 are likely mosfets. See my 2 seconds guide to see if they are shorted.
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    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.

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    Comment

      #3
      Re: Lenovo ThinkVision L2440pwC stays black

      Thanks for the fast reply. You were right, Q107 and Q108 are MOSFETs. They are model P609 by Alpha & Omega (datasheet: )

      I checked them in-circuit according to your MOSFET guide in post #19 using two different multimeters.

      All connections you asked me to test are high-resistance (one multimeter shows them as overload, the other one shows them between 2 and 8 Megaohms). So I guess they are fine.

      What else would be a good idea to check?

      Comment

        #4
        Re: Lenovo ThinkVision L2440pwC stays black

        If the panel is working this means you can rule out the logic board and TCON, therefore:

        - One or more CCFLs is faulty or has burnt wiring (try swapping them out one by one with a known good bulb).
        - Inverter is failing. This could be bad capacitors on the inverter or bad transformer(s). Check the resistance matches across the windings of each of them.
        - Power to inverter from the PSU is failing.

        Generally I would tend to do a full re-cap (except the great big one) as blown capacitors don't often exhibit visual symptoms and it's a lot cheaper than investing in ESR testers. You would have to de-solder them in any case to get an accurate ESR reading. Then I would go from there once you've ruled those out. Always double check your solder work, use Lead/Tin solder and a lot of liquid flux. Work slowly and calmly - good luck!
        Last edited by leapius; 03-12-2013, 07:05 AM.

        Comment

          #5
          Re: Lenovo ThinkVision L2440pwC stays black

          Originally posted by Neon View Post
          What else would be a good idea to check?
          On the connector between the power board and main/logic board, report all the DC to voltages for all pins. Report them here like so.

          Pin 1, on/off = 3.001V DC
          etc
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          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

            #6
            Re: Lenovo ThinkVision L2440pwC stays black

            Ok, after a few days of tinkering with this monitor whenever I found some spare time, here are the results:

            I did what retiredcaps suggested. While measuring the voltages on the connector on the power board, I noticed that the screen was on again. Happily, I reassembled the screen, just to find out it did not want to turn on again after reassembling.

            So I disassembled it again and applied some contact cleaner spray on said connector. Our electronics guy has also resoldered several joints on the power board.

            Now the behaviour of the screen is as follows:

            It lights up and stays on. However, a hissing noise is heard from the end of one of the CCFL tubes. The brightness flickers irregularly at several Hz. Brightness variation during flickering is in the upper range of brightness, I'd say between 80 % and 100 % of maximum brightness.

            What can I do now?

            Comment

              #7
              Re: Lenovo ThinkVision L2440pwC stays black

              Verify a bad bulb / wiring by substituting a test bulb. If you dont have any in anything you could use a Budm special
              https://www.badcaps.net/forum/showth...ght=test+lamps

              Then all you can do is to strip panel down to the lamps and either replace the
              faulty one ,or if it is clear that it is wiring - re wire it.

              We have a couple of links with advice on this, when you get there.
              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: Lenovo ThinkVision L2440pwC stays black

                Thanks to all for your input! The screen is fine again.

                I disassembled it completely and found out that the connection between the cable and the hissing CCFL was loose (see pics attached to this post). So I removed the old solder and resoldered the connection (and also the connection to the other CCFL right next to the one that was loose).

                The original insulation was a silicone part (in the pics: the white block) which I guess was molded around the joints between the cable and the CCFLs. It was damaged while I tried to reinsert the cables, so I added some insulating tape.

                Now the screen has been running fine for a few hours. There still is a hissing sound when I start it. However, the sound is way 'smoother' than before, which somehow makes it sound less agressive or dangerous. It also goes away after some time. I'll keep an eye on that corner of the screen to see if any smoke comes out.

                Thanks again for your help! I can't say which one of your tips / my actions did it, but at least it's back to life. One more screen saved.

                Picture description:
                1 and 2: before repair
                3 and 4: after repair
                Attached Files
                Last edited by Neon; 03-26-2013, 09:54 AM. Reason: Picture description added

                Comment

                  #9
                  Re: Lenovo ThinkVision L2440pwC stays black

                  Well done and thanks for reporting back what you did. Neat Job.
                  Ordinary insulation tape may not lastit gets very hot in there and high voltage. I think you can get special high temp tape and replacement silicon plugs. (if it doesnt last)
                  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: Lenovo ThinkVision L2440pwC stays black

                    Good post here!

                    I recently got one of these units at work, when I plug it in I quickly see the Lenovo logo come up then the screen goes dark. I'm guessing it could be something similar.

                    Not sure if it's even worth the time to open this up and check it considering these days the monitors are pretty cheap.

                    Cheers

                    Comment

                      #11
                      Re: Lenovo ThinkVision L2440pwC stays black

                      it's been arcing... was the solder joint on the CCFL itself still any good, not black and broken?

                      You better use capton tape, it's high temp electronics tape, good for insulation, protection and it sticks very good also.

                      Comment

                        #12
                        Re: Lenovo ThinkVision L2440pwC stays black

                        When I found this thread I thought my Lenovo ThinkVision L2440pwC was candidate for a solution as I read Teredactle's comment. It worked fine from the time I bought it until I had to move it upstairs to protect it from Hurricane Hermine water coming in the house. After the move, sometimes it would produce output from a PC, other times not. I broke it down looking for what Neon found, but saw no evidence of burning or overheating. I put it back together without changing anything more than contaminating an output layer spraying contact cleaner when I thought I had the air blaster can. Now it's working.

                        Comment

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