HP 1955 - Backlight not working

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  • fabianard
    New Member
    • Jul 2021
    • 3
    • Sweden

    #1

    HP 1955 - Backlight not working

    Greetings,

    I have a HP H1955 monitor. The monitor is obviously old (from 2005) and a similar replacement monitor wouldn’t be particularly expensive and hard to get hold on. The problem is that I'm using it for a custom built special purpose so it would be tedious and might take a while to find an exact replacement.

    Description of problem
    Suddenly it went black during use. When I restarted it, it stayed on for 1-2 seconds then went black again. This was repeated a couple of times. Then a burned smell came from the monitor and from that point the backlight was not coming on at all anymore. However the video processing is obviously still working. If I light on it with a flashlight I can clearly see the image. Thus I conclude that it’s a problem with the backlight.


    Troubleshooting so far
    I found lots of information regarding problems with this type of monitor in this thread:
    https://www.badcaps.net/forum/showthread.php?t=8598
    However, my board doesn’t seem to be identical so I’m not entierly sure what to check more than I have already done.

    I have found the following problems so far:
    • What appears to be a faulty solder on one of the gray caps (see attached image).
    • Shorted transistors: When I measure the resistance, the two C5707s transistors on the sides of the gray cap with faulty solder show no resistance, however I measure them. The two others seem fine. (See attached images.)
    • If I measure resistance over the fuse (see attached image marked "PF701" on the board) I get 139 Ohms when tested in circuit. I guess that may indicate that it’s been burned. Or do I need to desolder it to test it? (according to the link above, no backlight at all may indicate a burned fuse).


    Questions
    1. Before ordering parts, what additional troubleshooting can I do and how can this be done?
    2. According to this post https://www.badcaps.net/forum/showpo...3&postcount=15the “fu9024” should be checked for shorts. However. I’m not sure which part this would be and how it should be tested.
    3. Is it worth a shot to fix this? Or is it likely that any irreparable damage has occured?
    4. If I find another HP monitor of similar age, say with other dimensions, are the power supply boards swappable?


    Sorry I'm not used to working on PCB:s but I’m a quick learner and have basic knowledge and soldering tools. Any help in getting this sorted would be greatly appreciated.

    Thanks so much and cheers from Sweden.
    Attached Files
    Last edited by fabianard; 07-16-2021, 12:00 PM.
  • senndogg
    Badcaps Veteran
    • Dec 2011
    • 383
    • Albania

    #2
    Re: HP 1955 - Backlight not working

    Hello fabianard and welcome to the forum!

    This is a well known problem which i remember very well, repairing lots of these Benq PSUs.

    In general, there a 7 elements failing, 4x C5707 , 2 x FU9024 also the PF701 3A fuse.
    You can buy them as a kit, (if they are still available, its been a while i dont see these monitors around) or separate.
    It is discussed in this forum before, that it is essential to resolder the joints mainly the transformer legs, as this board suffers a lot.

    I think its a simple job, follow the first link you have mentioned, you cant go wrong.
    Good luck!

    Comment

    • fabianard
      New Member
      • Jul 2021
      • 3
      • Sweden

      #3
      Re: HP 1955 - Backlight not working

      Originally posted by senndogg
      Hello fabianard and welcome to the forum!

      This is a well known problem which i remember very well, repairing lots of these Benq PSUs.

      In general, there a 7 elements failing, 4x C5707 , 2 x FU9024 also the PF701 3A fuse.
      You can buy them as a kit, (if they are still available, its been a while i dont see these monitors around) or separate.
      It is discussed in this forum before, that it is essential to resolder the joints mainly the transformer legs, as this board suffers a lot.

      I think its a simple job, follow the first link you have mentioned, you cant go wrong.
      Good luck!
      Thanks for your answer! Unfortunately, parts seems to difficult to get hold on. I found that a Dell 1908FP with its bezel removed has almost the same physical dimensions as the HP monitor. In the end it was a cheaper option to just scrap the HP monitor.

      For future reference, I think that the NTE2668 available at TME.eu maybe could serve as a replacement for the C5707.

      Comment

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