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help to repair KVM Switch

Discussion in 'Troubleshooting and Repair' started by dariush, Jun 26, 2013.

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  1. dariush


    Jun 26, 2013
    my kvm switch model D--LINK 121 doesn't work and one buzzer sounds Thegh Thegh. i guess an alternator voltage on the board cause this but i dont know whats the sours of this alternator voltage?
    do you know? help me...
  2. shrtrnd


    Jan 15, 2010
    Not sure exactly what the problem might be, but it sounds to me like you're describing
    a relay problem?
    Is there a relay on the board? You may have lost the diode across the relay coil, causing
    the 'alternator voltage', that's buzzing your relay contacts?
  3. dariush


    Jun 26, 2013
    i cant find any diode on the board near the relay[ NEC UB2-4 5NU ]
    AND i dont have schematic of this board can you take me pls?
  4. dariush


    Jun 26, 2013

    i cant find schematic for kvm switch model D-LINL 121
    any body take me that?

    Dariush ... please dont post same topic in multiple threads again
    Last edited by a moderator: Jun 26, 2013
  5. shrtrnd


    Jan 15, 2010
    Is 'kvm' the company that made your switch?
    You get the most help here when you supply us with as much information as possible
    about your problem.
    Did you try contacting the manufacturer, and asking if it's possible to get a schematic
    from them?
  6. shrtrnd


    Jan 15, 2010
    A quick Google check of relay (NEC) UB2-4 5NU, shows that it's a 4.5VDC relay.
    You'd only have a diode across the coil if it was an AC relay, so I gave you the wrong
    advice to check.
    I see from your other post, you're trying to get a schematic of your board, which is the
    best thing you can do to troubleshoot your problem.
    (Try not to post questions about this problem on several different category topic headers,
    or the Moderators are going to correct you. They try to keep all the questions about
    one problem together, it helps with a more complete understanding of your problem)
    If you successfully obtain a schematic, it will be a lot easier to isolate your problem.
    The first thing to check, would be to make sure the board itself is the issue.
    Are you pretty sure the signal or signals being input to your board are correct?
    The second most commom problem to look for, would be a problem with the power
    supply to your board. You may be picking-up AC line frequency, causing your buzzing
    Are there any markings on the board itself, test point voltage values?
    If there are, it would be helpful to check them, and see if the voltages on the board
    are correct. That's a good place to start.
    (An example is your NEC relay. When tripped, you should read about 4.5VDC on
    the coil)
  7. davenn

    davenn Moderator

    Sep 5, 2009

    KVM = Keyboard,Video,Mouse
    they are a small unit that you plug those 3 and 2 computers into
    designed to share those 3 items

    to the OP you are not likely to find a schematic .... only chance would be the manufacturer


    EDIT: threads have been merged
    Last edited: Jun 26, 2013
  8. shrtrnd


    Jan 15, 2010
    Thanks davenn.
    Learned my new thing for today.
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