cause of bad caps in new equipment

Discussion in 'General Electronics Chat' started by mladen82, Mar 4, 2009.

  1. mladen82

    Thread Starter New Member

    Mar 2, 2009
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    Recently i repaired new (about 100hours worked) lcd 19'' monitor which had two 1000uF/10V/105C bad (bulged, each to other) electrolytic caps in output stage +5.1V of smps/inverter. Also main scaler board (which is supplieed with +5.1V) was dead .

    Can we exactly find main cause od this failure? Are caps simply low quality or there was some over voltage maybe?
    Why main scaler board was dead too?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Electrolytic capacitors tend to fail if they are old.
     
  3. mladen82

    Thread Starter New Member

    Mar 2, 2009
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    0
  4. mik3

    Senior Member

    Feb 4, 2008
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    The monitor is new but the capacitors may were old.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Electrolytics (and polarized tantalum caps) can fail quite rapidly if they're stressed after sitting idle for long periods of time, due to high leakage currents.

    They can frequently be reconditioned by charging them gradually to their rated voltage through a resistor (10k or larger) while monitoring for leakage current until the leakage current is within specifications. The slow charging re-forms the dielectric, without generating the heat that would otherwise result.

    This Google search for "capacitor reforming" returns lots more information:
    http://www.google.com/search?hl=en&q=capacitor+reforming

    There have also been reports of certain Asian capacitor manufacturers using too strong of an electrolyte solution, which boosted the capacitance ratings (for a short time) but caused rapid corrosion of the foil plates and early failure of the capacitors.
     
    PackratKing likes this.
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