cause of bad caps in new equipment

Thread Starter

mladen82

Joined Mar 2, 2009
3
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?
 

SgtWookie

Joined Jul 17, 2007
22,201
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.
 
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