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    #1

    Seeing noise finding similar posts (whats this called?)

    I see monitors that come in and have what I can only describe as noise comming from the outer corners of the LCD's. Does anyone know what I'm talking about and what's the correct terminology for this and what causes it?

    I fix my fair share of LCD's and after purchasing an ESR meter I've got a very high success rate but when I see one come in and it has this noise, which starts off not so bad but gets worse the longer the monitor is on, like it has a bad cap. When I first saw this problem, it was on a Xerox 17" flatpanel and I thought at first it was a cable issue, I didn't have an ESR meter then so I just replaced all the caps on the PSU and nothing changed. After getting a meter I've ran into one Mag that had the same problem but even worse, several of the filtercaps were bad and I replaced them but it did not cure the problem completely. I guess the Xerox may have had nothing to do with the mag's problem and vise versa but when I see a monitor with lines jumping and you can still see picture but it's got these dancing lines, what does everyone call that and where are they discussed?

    Thanks for hours of entertaining reading!!!


    Chaiyz
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    #2
    Re: Seeing noise finding similar posts (whats this called?)

    Originally posted by Chaiyz
    I see monitors that come in and have what I can only describe as noise comming from the outer corners of the LCD's. Does anyone know what I'm talking about and what's the correct terminology for this and what causes it?
    Outer corners -> Arcing on the CCFLs?
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      #3
      Re: Seeing noise finding similar posts (whats this called?)

      Originally posted by retiredcaps
      Outer corners -> Arcing on the CCFLs?
      Oops, never mind. I re-read and thought you meant hearing noise from the LCD corners?

      Now I know you are talking about the display.
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        #4
        Re: Seeing noise finding similar posts (whats this called?)

        Noise usually comes from the SMPS transformer or filter chokes, sometimes from the inverter transformer too. Nothing that a little varnish won't fix.
        Originally posted by PeteS in CA
        Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
        A working TV? How boring!

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          #5
          Re: Seeing noise finding similar posts (whats this called?)

          Are you referring to an audio noise, or a problem with the display on the panel? If the latter, I'd suspect a problem on the logic card. Check the voltage regulators.

          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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            #6
            Re: Seeing noise finding similar posts (whats this called?)

            Originally posted by Th3_uN1Qu3
            Noise usually comes from the SMPS transformer or filter chokes, sometimes from the inverter transformer too. Nothing that a little varnish won't fix.
            Could you please explain? I'm clear that you are referring to varnish to clean something but the answer was a bit vague for me. I think your on the right track thought and I'm really wanting to understand this problem. Also, the noise is not audible. Noise on the screen like when you have a bad monitor cable and it puts noise on the desktop.

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              #7
              Re: Seeing noise finding similar posts (whats this called?)

              Originally posted by Chaiyz
              Could you please explain? I'm clear that you are referring to varnish to clean something but the answer was a bit vague for me. I think your on the right track thought and I'm really wanting to understand this problem. Also, the noise is not audible. Noise on the screen like when you have a bad monitor cable and it puts noise on the desktop.
              Varnishing the transformers to isolate interference
              There are 10 kind of people in this world: those that understand binary, and those who don't.
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                #8
                Re: Seeing noise finding similar posts (whats this called?)

                Originally posted by Chaiyz
                Also, the noise is not audible. Noise on the screen like when you have a bad monitor cable and it puts noise on the desktop.
                Well you should have made yourself clearer. I was talking about audible noise. Dipping the transformers in varnish will quiet them down if they're noisy, but it won't do nothing for your picture.

                Hmm, video interference. I've mostly seen that on LCDs with VGA inputs only, because the signal is converted from digital to analog once in the video card, then back again to digital in the monitor. If the PCB layout is messy and the A/D converter is too close to the power supply transformer, it will inevitably pick up interference. If you have an oscilloscope you can try checking whether the interference is caused by ripple (which can be fixed with new/more caps), or by the board layout (which can't be fixed, but you can try shielding the transformer to see if that makes a difference).

                IMO it makes no sense why they didn't use DVI in the first place - okay, compatibility is one, but making LCDs with only VGA inputs is dumb IMO.
                Originally posted by PeteS in CA
                Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                A working TV? How boring!

                Comment

                  #9
                  Re: Seeing noise finding similar posts (whats this called?)

                  Originally posted by retiredcaps
                  Outer corners -> Arcing on the CCFLs?
                  Really, arcing is a very distinct possibility. Unfortunately, it is very diffcult to troubleshoot as you have to disassemble the panel to confirm if the end of the lamps are arcing. I've seen some where the heat from the arcing caused the plastic panel inside the monitor to melt a bit!

                  I've also found ends grow red but stil light being emitted.

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