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It's my VX922 again - AC line noise?

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    #1

    It's my VX922 again - AC line noise?

    First off, my VX922 that I repaired a while ago is still working just fine

    EXCEPT, I noticed that when I have it powered on with display, it causes my computer speakers to have a low-toned hum to them. This only happens when it is actually displaying an image. If it is in standby, or off but plugged in, it doesn't do it. Seems to be in sync with the backlight turning on.

    If I have it unplugged from the computer, it still causes the hum in the speakers for the moment that the display shows "No signal" on the screen, before it goes to standby and gets quiet. So it isn't causing the noise through the DVI somehow, it has to be coming from the AC line.

    I just noticed this recently as I use it as a spare 2nd monitor that I use occasionally.

    So... I'm thinking I'm gonna take it apart again and look at it, but do any of you gurus here have a suggestion as to what what would cause that to happen and what I could try to do to fix it?
    Last edited by Sparky; 06-22-2010, 09:29 PM.
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    #2
    Re: It's my VX922 again - AC line noise?

    Originally posted by Sparky
    First off, my VX922 that I repaired a while ago is still working just fine

    EXCEPT, I noticed that when I have it powered on with display, it causes my computer speakers to have a low-toned hum to them. This only happens when it is actually displaying an image. If it is in standby, or off but plugged in, it doesn't do it. Seems to be in sync with the backlight turning on.

    If I have it unplugged from the computer, it still causes the hum in the speakers for the moment that the display shows "No signal" on the screen, before it goes to standby and gets quiet. So it isn't causing the noise through the DVI somehow, it has to be coming from the AC line.

    I just noticed this recently as I use it as a spare 2nd monitor that I use occasionally.

    So... I'm thinking I'm gonna take it apart again and look at it, but do any of you gurus here have a suggestion as to what what would cause that to happen and what I could try to do to fix it?
    The first question to ask is 'Is it something it's putting on the AC line, or is the noise being picked up by the audio input to the speakers?' Running the power cords for both the monitor and the speakers to separate filtered power strips (ideally with each power cord passing through a ferrite bead) would tend to filter out any garbage on the power lines. Or you can try keeping the audio cable to the speakers as far away from the monitor as possible.

    PlainBill
    For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

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      #3
      Re: It's my VX922 again - AC line noise?

      The transformer windings in LCD inverters will sometimes develop a loose winding causing a hum or 'singing'.
      I've heard of it getting so loud it can be heard through walls.
      Sometimes it goes away after a while, sometimes not.
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        #4
        Re: It's my VX922 again - AC line noise?

        also noticed this on my Belinea 101910 (which seems to be identical to some Viewsonic model .. can't remember which one. 19" 1280x1024 with MVA Panel and the FSP 035 PSU/inverter).
        sometimes i get a humming noise in my speakers (seperate ones. not the integrated 0.2W beepers), and other times there's absolutely nothing.
        haven't figured out WTH is causing this. it's humming again in the speakers right now, yesterday there was nothing.. strange
        Last edited by Scenic; 06-23-2010, 02:00 AM.

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          #5
          Re: It's my VX922 again - AC line noise?

          If you replaced with good quality, low ESR caps the first time around, then there isn't too much can go wrong with the power board.

          If you have spare CCFL lamps, you can also swap them in to troubleshhot the source. I once came across a set of lamps that are arcing inside.

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