HP w2408 LCD - Buzzing Noise when Brightness < 100%

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  • fritzycat
    New Member
    • May 2017
    • 8
    • USA
    #1

    HP w2408 LCD - Buzzing Noise when Brightness < 100%

    I have an HP w2408 LCD that makes a constant buzzing noise when the brightness is less than 100%. If I turn the brightness all the way up to 100%, the buzzing stops. It has been making this noise for years, I've just now decided to try to do something about it! Except for the buzzing, the monitor works great.

    I'm not sure if the issue is with something on the inverter board or the CCFL tubes themselves. I've been searching the forums, but haven't found another post that has a solution to this issue (yet).

    I've disassembled the unit, but I can't seem to isolate the buzzing to a single component. The buzzing starts immediately when the CCFLs light up after I power on the device. I've tried poking at each of the inverters with a plastic stick to see if the noise might change when some pressure was applied - it didn't. None of the inverters are showing any signs that they have been overheating.

    The capacitors appear ok - no bulging, burning or leaking of electrolyte.

    I tried disconnecting one of the CCFL tubes. When I do this, and power the unit on, the remaining CCFLs light up for about a second (without any buzzing!), but then the monitor shuts down about 1 second after that. I'm assuming this is because of some fault protection circuitry. It doesn't seem to matter which of the 6 CCFLs I disconnect - I get the same result - no buzzing, but the monitor shuts down after 1 second.

    I've attached a few photos for reference - the model number on the inverter board is QLI-002. A yellow sticker on the board has the numbers: 790111420000R S1100BA00NY33 0728

    Any suggestions on the procedure to troubleshoot this? I'll keep searching the forum to see if I can find anything...

    Thanks!

    -Fritz
    Attached Files
    Last edited by fritzycat; 05-19-2017, 02:46 PM.
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    • fritzycat
      New Member
      • May 2017
      • 8
      • USA
      #2
      Re: HP w2408 LCD - Buzzing Noise when Brightness &lt; 100%

      ... and moments after I posted my question I saw the excellent sticky post by 'retiredcaps': https://www.badcaps.net/forum/showthread.php?t=10419

      I'll probably start by replacing the capacitors (470uf 35v) because that is easy and the caps are 10 years old.

      If that doesn't do the trick, I'll try testing for dying CCFL tubes by disconnecting them one at a time and connecting another CCFL in its place. I'm just not sure if bad CCFLs buzz (or might cause the inverter to buzz) when they are going bad. Can anyone confirm this?

        Comment

        • fritzycat
          New Member
          • May 2017
          • 8
          • USA
          #3
          Re: HP w2408 LCD - Buzzing Noise when Brightness &lt; 100%

          So, I've got some 470uf 35V capcitors. However, they are temperature rated 105C. The capacitors on the inverter board are rated 125C. Can anyone tell me if the different temperature rating is relevant in this application? Do I need to order some 125C caps?

          Thanks!

            Comment

            • Ian Paul
              Member
              • Mar 2017
              • 23
              • United Kingdom
              #4
              Re: HP w2408 LCD - Buzzing Noise when Brightness &lt; 100%

              Transformers can buzz, is it coming from inverter board?

                Comment

                • fritzycat
                  New Member
                  • May 2017
                  • 8
                  • USA
                  #5
                  Re: HP w2408 LCD - Buzzing Noise when Brightness &lt; 100%

                  Thanks for the reply. The buzz does appear to be coming from the inverter board, but I can't seem to isolate the buzz to any one component. There are 12 transformers on the board so I thought I would start with replacing the caps to see if that helps. I haven't diagnosed an issue like this in the past, so I'm open to any and all recommendations.

                    Comment

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