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    #1

    Cibox Flat Screen "two seconds to black" problem...

    Hi,

    Found this great site a few days ago so just testing the water with my first posting, hoping someone out there may be able to help me…

    I have a Cibox C1905 TFT LCD Monitor Model No. LW1922C which is giving me grief. It appears to be suffering from the ‘two seconds to black' problem.

    When I was given this monitor it would work but turn itself off after a minute or two. I changed a couple of electrolytics which were showing signs of distress, my capacitance meter confirming their value had decreased considerably. This however has not affected a cure and the time the monitor will stay on has progressively shortened.

    The on/off light is always on, turning green when the monitor ‘sees' an input. It stays green even when the picture goes off. Removing the source signal the on/off light turns amber but immediately goes green when the source is reconnected. The monitor then produces a picture for a very short while then goes off. Likewise switching the monitor off and on brings the picture back but quickly goes off again.

    I seem to be able to see faint images with a torch when the screen is off.

    Chyenne had a problem (not the same problem as mine) with a similar monitor and posted some pictures which I have gratefully borrowed (thank you Cheyenne):-

    https://www.badcaps.net/forum/attach...8&d=1320597822

    https://www.badcaps.net/forum/attach...9&d=1320597822

    I do not have an ESR meter so cannot measure the ESR of the electrolytics. I do have a couple of DVM's and a capacitance meter. I always feel happier using an analogue meter to check diodes etc and I have ordered an analogue meter off eBay.

    I'd be grateful for any help.

    Incidentally I found a great ‘how to' on fault finding on flat screens, sure it was on this site but I can't for the life of me find it now…

    Thanks.
    Tags: None
    #2
    Re: Cibox Flat Screen "two seconds to black" problem...

    Originally posted by johnvvc View Post
    Chyenne had a problem (not the same problem as mine) with a similar monitor and posted some pictures which I have gratefully borrowed (thank you Cheyenne):-
    We prefer to see pictures of your boards for a number of reasons.

    1) Manufacturers make revisions or even complete board changes while keeping the same lcd model number.

    2) Your board, while perhaps the same, may have "aged" differently due to heat, cold, etc. Your board might have hot spots, poor soldering, glue turning conductive, etc.

    3) Just this month, someone posted I changed all the bloated caps, etc, but it doesn't work. It wasn't until he posted a picture of his recapped board that I spotted another bad capacitor.

    Now having said all the above, 2 seconds to black can be

    a) bad caps
    b) bad ccfl and/or wiring (mostly the return wire)
    c) bad inverter transformer

    All the above are explained in detail starting with posts #13 and #14 at

    https://www.badcaps.net/forum/showthread.php?t=10419
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    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

    Please do not post inline and offsite as they slow down the loading of pages.

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      #3
      Re: Cibox Flat Screen "two seconds to black" problem...

      retiredcaps - thanks for your input.

      Thanks also for that 'how to' link - that was the one I couldn't find and which I'll go off and have a read.

      Apologies for not posting actual photographs, I can see why that wasn't such a good idea

      I'll have a good look at this monitor when my new analogue meter arrives and post again if - no when - I need more advice.

      Thank you for your time,

      John

      Comment

        #4
        Re: Cibox Flat Screen "two seconds to black" problem...

        Had another look at this monitor.

        I suspect that one of the ccfl tubes is suspect. When I disconnect it and connect another one (while still inside another monitor!) the Cibox works - with 3 tubes instead of 4 running.

        As the picture is perfectly acceptable with 3 tubes, for now at least, I would like to run the monitor with 3 tubes but just disconnecting the suspect one and we're back to the old '2 seconds to black' scenario.

        I presume there must be some sensing circuit on the board that senses when a tube is disconnected (or broken) and turns the invertor off? If that is the case could I fool it into thinking it has 4 tubes connected... I'm thinking along the lines of some sort of dummy load, like a resistor across the tube socket.

        I'd welcome any ideas.

        Comment

          #5
          Re: Cibox Flat Screen "two seconds to black" problem...

          Originally posted by johnvvc View Post
          I presume there must be some sensing circuit on the board that senses when a tube is disconnected (or broken) and turns the invertor off?
          Correct. The pwm inverter chip operates as an "all or nothing". All tubes work or none at all.

          If that is the case could I fool it into thinking it has 4 tubes connected... I'm thinking along the lines of some sort of dummy load, like a resistor across the tube socket.
          Only one person has been able to get a "hack" to work. See

          https://www.badcaps.net/forum/showthread.php?t=13713

          If you try, this please post a picture and report back if it is working or not.
          --- begin sig file ---

          If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

          We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

          Please do not post inline and offsite as they slow down the loading of pages.

          --- end sig file ---

          Comment

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