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Motherboard caps

Discussion in 'Electronic Repair' started by purtnoy, Feb 3, 2005.

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  1. purtnoy

    purtnoy Guest

    Just replaced all the 2700 micr 6.3 volts, with 3300 mic 16 volt caps
    (the 3300 caps are twice as big around,(does that matter?) had to
    solder longer legs to raise them up, so they can fit without shorting
    them out. replaced a few other smaller caps also...........still the
    same as before, when I hook the power supply to the motherboard, 2 red
    lights glow on the motherboard, the CPU fan turns, power supply fan
    turns. when I hookup the monitor to the video card,the screen will
    not come on, green light just flashes, (monitor is good works with
    other computer) video card is good, and the ram is good.
     
  2. purtnoy a écrit :
    Sometimes there's a poor connection between mainboard and ram or Video
    card and ram. Try with an other card. Or, maybe because the bigger caps
    take more time to charge, the video card can't take it. Try to power on,
    wait and reset.
     
  3. Harvey

    Harvey Guest

    Is the CPU getting warm?
     
  4. James Sweet

    James Sweet Guest

    It's possible something else fried on the board when the caps failed.
     
  5. Gerard Bok

    Gerard Bok Guest

    Yes. In this case it does matter.
    In lineair systems, 'bigger is always better'. On your
    motherboard exceeding a capacity value by 50% could disrupt the
    entire regulator circuit.
    Basic operation in this case is based on energy stored in an
    inductor, periodically transferred via a (schottkey)diode into a
    low ESR capacitor.

    You can only replace those capacitors with types of roughly the
    same value, high temperature types and --at least as important--
    low ESR values.
    That also is unacceptable. This will introduce an extra induction
    ('coil') in series with the capacitor. Take a look at the coils
    surrounding those capacitors. And notice that they only have a
    few turns, hence very low inductance :)

    The circuit you are working on is likely to be the CPU stepdown
    regulator. That is a circuit that transforms 12 volts into
    something like 1.55 ... 2.55 volt. At several amperes.
     
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