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    Flaky HP L2035 LCD Monitor, hard to power on

    Hi all!!

    Few months ago my HP L2035 LCD monitor died, no green light.. Opened, and noticed that one of the capacitors 1000 uF / 25V is bulgy.. replaced it with a new one, and BOOM monitor is back and running!!

    However, after few months, it sometimes does not power on, and it takes a while for it to power on.. Took it apart, removed ALL capacitors and measured using a capacitor meter, all came OK, put them back, and monitor is working, but having hard time to power on, and sometimes goes off, but after it "warms up" seems to hold OK..

    My question, how do I go about fixing this ? or do I have to wait for it to die completely before I can debug ?

    I saw I can get a new p/s board for ~$20, but really the educational value is important here, as much as possible.

    Is there any measurements I can take now while it is working and compare to when it will not work?

    If you don't mind, pls be specific if possible HOW to measure, i.e. from "ground" or from one pin to another? I once measured a live board from wrong pins and that caused.. a small "explosion".. I gather it is always safe to measure to one of the screws/ground, and thats what I do when measuring live boards for DC/AC.

    Thanks much!!!
    Attached Files

    #2
    Re: Flaky HP L2035 LCD Monitor, hard to power on

    The big cap doesn't seem soldered properly.
    Try reflowing all the joints in the hot side.

    Comment


      #3
      Re: Flaky HP L2035 LCD Monitor, hard to power on

      Originally posted by stormy1777 View Post
      Opened, and noticed that one of the capacitors 1000 uF / 25V is bulgy.. replaced it with a new one, and BOOM monitor is back and running!!

      However, after few months, it sometimes does not power on, and it takes a while for it to power on..
      You should have replaced all electrolytic capacitors and not just one (except for the big 400V cap). Many monitors use crappy capacitor brands that often fail (especially since LCD monitors run hot inside). When you see that one capacitor has failed, that means the others are not far behind it in terms of health. I see Elite and Lelon capacitors in your monitor. Both of these brands have failed numerous times in other monitors.

      Also, measuring the capacitance won't tell you everything about the condition of the capacitor. Another important parameter is ESR (equivalent series resistance). There are specialized meters for that too, but the better ones tend to be expensive, so it is often more economical to just replace all of the caps in the monitor (especially if you don't repair things too often).

      Also, make sure to use good quality *Japanese* capacitors brands and appropriate respective series. Otherwise, your repairs might not last too long. When shopping for caps, AVOID eBay, especially any sellers based in China/HK. There are very very few sellers on eBay that sell genuine capacitors.

      Comment


        #4
        Re: Flaky HP L2035 LCD Monitor, hard to power on

        Thanks folks for this amazing support and great tips!! I'm re-reading and clinging to every word... Ok, re-soldered all the capacitors (see image), since I'm not sure my hot-air (reflow) will do a good enough job.

        After the re-solder, it worked for an hour, turned off/on 10 times, all OK, then left connected to electricity but turned OFF, now it does not turn on at all...

        pushing the ON button, and the green light blinks a bit, then turns off...


        momaka - I hear you about capacitors...

        I'm using this meter, and all came with pretty low/same values:

        https://www.youtube.com/watch?v=GfJizkJB21M

        Let me replace all of them and see!!

        Beyond that, is there any way to "debug" somehow, by "tracing" the board, I'm guessing that requires way more knowledge than I currently have

        If anyone is aware of a training/youtube or the like (on any other/similar board) I'll be happy to know..

        I'll report back once all caps replaced

        Thanks!
        Attached Files

        Comment


          #5
          Re: Flaky HP L2035 LCD Monitor, hard to power on

          oh my.. pressed button once, it blinked the green light but LCD didn't turn on.. I left it like that, and after ~20min it turned ON FULLY, and image was perfect.. I guess based on that does that sound like the caps are bad? or something else has such symptom?

          Thanks.

          Comment


            #6
            Re: Flaky HP L2035 LCD Monitor, hard to power on

            Originally posted by stormy1777 View Post
            oh my.. pressed button once, it blinked the green light but LCD didn't turn on.. I left it like that, and after ~20min it turned ON FULLY, and image was perfect.. I guess based on that does that sound like the caps are bad? or something else has such symptom?
            Typically, if monitor only starts when warmed up or if it has a delayed start - points to either faulty output caps or faulty start-up cap problem. In more rare cases, there can also be bad caps on the logic/video board after a regulator.

            Post a picture of the video board so that we can take a look at it, just in case. The video board usually has only small electrolytic caps. And the thing about those is that they rarely bulge when they fail. Most of the time, they look fine but they develop high ESR.

            Also, speaking of small caps... next to that large green 400V cap, there are two small green Lelon electrolytic caps. Make sure to replace those as well when you are replacing the others. They are usually rated in the order of 1 to 100 uF and 16 to 50V. One of them is the start-up cap I was talking about above. Basically, they provide power to the power supply controller, and if that is unstable, then the power supply may not start (properly) or may take a while for it to start.

            Originally posted by stormy1777 View Post
            Ok, re-soldered all the capacitors (see image), since I'm not sure my hot-air (reflow) will do a good enough job.
            You shouldn't use hot air for removing or installing capacitors. Hot air is for SMD parts only. Your soldering looks good on that last picture. If you get flaky-looking or joints or ones that aren't smooth, then just apply some flux (liquid or paste, rosin type R or RMA) and re-heat the joints again with your iron. They should come out nice and smooth.

            However, that hot air can come handy . One thing you can do is to leave the monitor to cool off so that it doesn't turn on anymore (make sure to test that while it is cold). Then, using the hot air, heat up various caps slightly (like no more than 100 C/ 212 F) and see if that makes the monitor turn on. The reason why that works sometimes is because as electrolytic capacitors warm up, their ESR drops, which might allow the circuit to just start working again. This also explains why it takes a while for your monitor to turn on - as the caps inside get heated up, their specs improve a slight bit.

            Originally posted by stormy1777 View Post
            Beyond that, is there any way to "debug" somehow, by "tracing" the board, I'm guessing that requires way more knowledge than I currently have
            There is. And monitor power supplies like this actually tend to be very simple and straightforward to troubleshoot. But since the power supply is working, the easiest and safest route is to replace the caps first to rule that out as a source of problems (especially if the caps are a brand known to fail).
            Last edited by momaka; 12-01-2015, 10:12 AM.

            Comment


              #7
              Re: Flaky HP L2035 LCD Monitor, hard to power on

              I'm so sorry for not reporting sooner, just wanted to tell you, your reply was HUGE HUGEly appreciated! and explained a lot of unknowns.. In fact, the heating TRICK you mentioned DID work, and the monitor did power on once these TWO capacitors were heated!!!!!!

              I wish I could give you bonus points somehow, in any event, ordered these capacitors since I don't have them handy... Thanks much!

              Comment


                #8
                Re: Flaky HP L2035 LCD Monitor, hard to power on

                Well, keep us posted what happens, even if this is a month later.

                Comment


                  #9
                  Re: Flaky HP L2035 LCD Monitor, hard to power on

                  Sorry to bump such an old thread, but it DID work monitor did power up, and still functioning

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