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Latop surface component breaks off

Discussion in 'Electronic Repair' started by looking, Feb 1, 2013.

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  1. looking

    looking Guest

    Hi,

    I disassembled a laptop to replace the power jack and during the
    process dislodged a [tiny] surface component.

    It doesnt look like it has leads of any sort. It's beige. A resistor?
    A cap? Need help. It's off the board and I'm hoping it's
    unidirectional and that it can be soldered back and all will be well.

    I'd appreciate any comments.

    looking.
     
  2. looking

    looking Guest


    Thanks for replying. That's about what I found out and I got the unit
    back up, albeit without apparent battery functionality, and a slight
    off color smell. Powered down after a few minutes but on the second
    boot-up, the box was on breifly and then went blank after a pop. I
    disassembled back to the MB and the dislodged capacitor I had soldered
    back on had had some malfunctrion and was no longer soldered on.

    I know it's a capacitor per writing on the MB, PC108. It's in a group
    of 3 and after soldering the pc back and reassembling the laptop, I
    check omhs across each of the 3 caps and all read about 113-116 on a
    VOM.

    Trying to be brief: it's tight in there particularly since the power
    jack has been resoldered, but I'm still hopeful about the repair. The
    unit did function after try 1, so I think that if I can get the cap
    back in there, there's a good chance of success as caps do fail,
    people replace them and th eunits function even if there is a pop when
    they fail?

    In the back of my mind, I still wonder about the polarity issue though
    I can't see how to tell one side from the other. Unless I'm using
    magnification? Am I correct to be concerned? Have I provide enough
    info to determine?

    From where I am, I need a replacement cap. Can I go to the stockpile
    of old boards and eyeball a replacement? Or is this the kind of repair
    that I might be able to get done a shop that might bail my sorry butt
    out?

    Lastly, it's hard to desolder. Do you have a toll recommendation?

    I just checked out the link, it is an MLCC. I haven't finished reading
    yet, Would this component be heat damaged in a bad soldering job?

    Thanks for listening.
     
  3. mike

    mike Guest

    You want to measure the cap BEFORE you solder it back in.
    Measure the volts across the pads it fell off and put that many volts
    on the cap for a while and see if it heats up.
    It will take half a millisecond for someone to give a hundred examples
    where the following is not true...but...statistically...
    removing any one of the caps on the motherboard will likely NOT cause it
    to fail completely/catastrophically.

    Are you absolutely/positively sure you have the right replacement jack.
    Not all have the same pin connections, even if they fit the holes.
    I'd check for shorts under the jack and in the vicinity where you
    soldered. The fact that the AC supply function didn't work is a clue
    that something is wrong there.

    I have no idea your electronics experience level or the equipment
    you have available.
    There's a common power supply failure mode.
    The internal resistance of electrolytic caps starts to increase
    as you stress/age them.
    If you start with 20V and switch it down to 3.3V for the processor,
    the series resistance starts letting those voltage spikes through.
    Eventually, you have a node that still reads 3.3V on your VOM, but
    if you put a scope on it, you see 20V spikes with an average voltage
    of 3.3V. The caps on the 3.3V node don't like the spikes.
    Nor does the processor that it is driving. It may still work, but
    have enough internal damage to overheat itself.

    This can happen in the external AC supply and/or any of the switchers
    internal to the laptop.

    I've seen open power supply caps take out all the IC's on a monitor
    board.
    This is not typically a problem for small caps like you describe.

    You can look with a scope if you can put all the heat sinks back on
    with it disassembled and still get at the part in question.

    Are we having fun yet?
     
  4. Guest

    There is a good possibility that you can just leave it out. There are lots of those caps all over the place and since this one is near the power jack it most likely only reduces EMI slightly.

    Chances are you overheated it reinstalling it. The first thing I would do is to see if it will fire up without it because there is a good chance someting else is fried now.

    Hopefully that will just be a fusible link of some type.

    Computer equipment generates EMI all over the place. The PS is switched mode so it generates. There will be regulators on the mobo which are also switched mode. Those caps generally smooth out the HF ripple not sufficiently filtered by the crapola SMD electrolytic nearby. This is not necessary for the operation of the circuit usually in a case like this. When you see one near a big damn chip, that is a different story.

    But this is almost assuredly in the primary/power/charging circuit.

    If the thing runs without it, consider just leaving it that way. I'd say the odds of it still meeting FCC and CFR requirements are about 90 %
     
  5. Franc Zabkar

    Franc Zabkar Guest

  6. Guest

    Hmmmm, the more things change.........
     
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