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newbie advice - please identify this component

Discussion in 'Troubleshooting and Repair' started by bobalob, Mar 31, 2011.

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  1. bobalob

    bobalob

    2
    0
    Mar 31, 2011
    Hi All,

    I'm trying to repair a router, if I do a continuity test on the power input all of the pins are bridged so I took a look to see what the problem is. I've seen a component which looks a bit worn out and which bridges the pos/neg power input tracks.

    It looks like it's specifically oriented based on the picture on the PCB so I'm guessing it's a diode but don't really know.

    I took a pic so you can see - if someone could identify it either way and maybe give an explanation as to why it bridges the power rails I would be extremely grateful.

    [​IMG]

    Uploaded with ImageShack.us

    Thanks in advance,

    Dave.
     
  2. davenn

    davenn Moderator

    13,799
    1,940
    Sep 5, 2009
    yes its a diode board part D8 it also shows you the circuit orientation for it
    see the pic to the left withthe the looped drawing and the A and K below it

    if it bridges the power rails then is probably a reverse polarity protection diode
    which is usually done like this....

    [​IMG]

    you can see that in that configuration with the power connected correctly, the diode doesnt conduct and the circuit operates normally.
    BUT, if you accidentally reverse the power polarity, then the diode will conduct with almost short circuit condition and that resulting hi current flow will blow the fuse.

    Hopefully some where in the power supply of your unit there is also a fuse? :)

    Dave
     

    Attached Files:

  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    It's a diode allright. They're often placed like that to short out the power supply should it be applied with the wrong polarity, thereby protecting the costly router electronics.
    It seems to be smaller than the types I'd expect to be used for that kind of duty though. It's been hot but are you able to identify the color of the bands?
    Also, an overview shot of the power input area there might help us verify it's function. That's the best closeup I think I've seen on this site to date btw..
    Edit: Dave beat me to it.. :)
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    :p :p haha ;)

    Dave
     
  5. bobalob

    bobalob

    2
    0
    Mar 31, 2011
    Thanks for all your help guys, i pulled the diode off the board and hoping it was only for reverse polarity protection i plugged it it!

    It works! :)
     
  6. davenn

    davenn Moderator

    13,799
    1,940
    Sep 5, 2009
    cool, so chances are the diode is probably cooked. A replacement rated at maybe ~ 2A would be an ok replacement

    D
     
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