Short circuit occurring in AC adaptor to power jack on motherboard

Discussion in 'General Electronics Chat' started by some_weird_kid, Jan 17, 2007.

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  1. some_weird_kid

    Thread Starter New Member

    Jan 17, 2007
    I am a new member here, with a moderate level of electronics knowledge. I took a course in high school and do some simple soldering for a hobby. My current problem is as follows: I bought a broken laptop computer with the intention of investigating it a little bit and hopefully being able to do some repair work. The motherboard does not power on, but I have pinpointed the problem to the power jack on the motherboard. Originally, the center pin was not making contact with the voltage pin in the motherboard, which I corrected with some solder. This did not fix the problem entirely, however, because a new problem has stood up. Here it is as it stands at this moment, most of this done with a conductivity test on a multimeter:
    When the power jack (on the motherboard) is not plugged in, I do not have any conductivity between the voltage and the ground pins from the jack, which is how it should be in my understanding.
    When the AC adaptor is plugged into the power jack, I notice sparks and clicking, a sure sign of a short. Also, a conductivity test shows conductivity between the ground and voltage pins. I have surrounded the outside and back of the jack in electrical tape to eliminate that as a possibility for a short. It seems as though the short is occurring within the jack itself.
    A conductivity test on the jack itself does not show any conductivity between the inner contact of the adaptor and the outer (ground) metal covering.
    When using a different adaptor, plugged only into the motherboard jack and not the wall, this conductivity is still present between the voltage and ground pins.

    I hope this is enough information to understand the problem. I suppose my first and most important question is simply whether or not this is normal. I am pretty sure from my experiences with electronics that the ground and voltage tracks should not bridge, especially right at the power jack. Is this incorrect? Also, are there any tips for further diagnostics or solutions I could try? The only option I can think of is to remove the power jack from the motherboard and attempt to replace it with a comparable one. Again, I'm not completely new to electronics, but I'm no expert. Any help that anyone could provide would certainly be much appreciated. Thanks for your time.
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
    If you can, desolder and remove the connector. That requires more skills than a simple message will be able to impart. Once it's off the board examine the board for damaged traces, clean it carefully with alcohol and foam swabs. Do a continuity check on the jack and see if there is a short on the board or if it's gone.
  3. some_weird_kid

    Thread Starter New Member

    Jan 17, 2007
    Thank you for the help. I do have a little experience with desoldering components from a motherboard and, while the multiple connections of this jack will be a challenge, I think I will be able to handle it. Thank you very much for your suggestion.
  4. beenthere

    Retired Moderator

    Apr 20, 2004

    If the short is still there with the jack gone, see if you can find any capacitors that have become discolored or gotten taller. This is a total failure for a desktop, but may be repairable on a portable.
  5. bertus


    Apr 5, 2008

    Do you realize that this is a more than 4 years old thread?
    Let it rest.

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