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Can anyone explain this self healing mystery.

  1. Mar 16, 2009 #1

    uart

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    Can anyone explain this "self healing" mystery.

    Can anyone think of any type of failure mode in an electronic component that could account for the following weird case of my self healing LCD monitor.

    ----------------------------------------

    I've got this LCD monitor that's got a weird problem. If I put it in use then after a number of days or weeks of operation it will fail to start. It behaves as if it had no power connected, there is no display and the green "power on" LED doesn't even light up.

    Once it's started, if I set the computer power management to "turn the monitor off : never", then it will work indefinitely as long as the computer is left running. However when I turn the computer off and try to restart, the monitor may not start up (it acts as if it had no power as described above).

    The problem actually gets progressively worse. At first the monitor starts up properly all the time, then after a while it will not start up if you try to power up within a few minutes of shutting down (in other words you have to have AC power off for a few minutes before re-powering up). Then it progresses to the point where you have to leave AC power off for an hour or more or it wont start and eventually it gets so bad that you have to leave it overnight, and eventually even that wont do the trick.

    But here's the really weird part, take it out of service for a month or so and then re-test it and it's back to working all the time (though it will deteriorate exactly as before if you keep using it for a number of days or weeks).

    BTW. The model is : Samsung Syncmaster 173V
     
    Last edited: Mar 16, 2009
  2. jcsd
  3. Mar 16, 2009 #2
    Re: Can anyone explain this "self healing" mystery.

    Have you tried putting it in the dishwasher?








    just kidding
     
  4. Mar 16, 2009 #3

    uart

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    Re: Can anyone explain this "self healing" mystery.

    Hmmm a joke I know, but I don't get it?

    Anyway I think putting it the rubish bin is more appropraite :p. I don't use it anymore but it does make an ok emergency spare. I know that if I keep it stored it will definitely work at least for a day or two, say if my current monitor dies suddenly or whatever. It would be better than nothing while I was waiting to get a replacement. :)
     
    Last edited: Mar 16, 2009
  5. Mar 16, 2009 #4

    berkeman

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    Re: Can anyone explain this "self healing" mystery.

    Sounds like there is a floating CMOS input somewhere that is confusing the control circuitry. If you're lucky, maybe it's in the connector, so be sure to unplug the monitor cable and inspect the pins. Less lucky would be a connection inside the monitor, like at an internal connector, or an open trace on the PCB or a bad solder joint on an IC. You might open it up to look for stuff like that, if you're comfortable with it. Obviously unplug the AC cord before you open it up...
     
  6. Mar 16, 2009 #5

    uart

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    Re: Can anyone explain this "self healing" mystery.

    Good suggestion, thanks berkeman.

    Actually when it first start to happen (and I only had to turn it off for a few minutes before restarting) I was pretty sure that it must be a thermal problem. As the problem got worse I quickly realised that the time constant involved was far to long for a thermal issue. Another theory I had was that perhaps a capacitor was degrading and the leakage current was increasing over time, but I didn't know of any "automatic healing" process wrt capacitor leakage when the capacitor is left discharged for long periods. Are you aware of any capacitor type and related "healing" processes that could be relevant here?

    Anyway the floating cmos gate is not a bad theory, it could in principle involve a very long time constant eventually leading to failure to start. It wont be as simple as in the monitor cable or pins though, when this problem happens the monitor wont even power on (as in the green power LED wont even light up). A working monitor will still power on fine with the monitor cable disconnected, so that cant be the problem. If it is a floating cmos gate issue then based on the symptoms I'd say it would be something that can prevent the power supply circuit from starting.
     
  7. Mar 16, 2009 #6

    turbo

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    Gold Member

    Re: Can anyone explain this "self healing" mystery.

    I agree with berkeman that you might first want to suspect something mechanical in a connection somewhere. If you have a separate video card (not integrated on the MB) open the PC, remove the card, then re-seat it. Unplug and re-connect cables at the monitor (if there is a plug-in connection there) and at the video card several times to wipe the contacts. Fingers crossed!

    Edit: you got in ahead of me. If the darned thing won't power up stand-alone... hmmm.
     
  8. Mar 16, 2009 #7

    uart

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    Re: Can anyone explain this "self healing" mystery.

    No the problem is definitely independent of the video card or computer or cable. Those were the very first things I ruled out when it started to fail.
     
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