Testing Capacitor

Have you ever came across power problem where once you 'on' the power supply and the fuse blow? You have checked all the components in the power section (primary) and secondary section and all the components working fine! Where is the culprit? A fuse blown are usually caused by a shorted rectifier, defective posistor, field effect transistor or FET, shorted primary winding of switch mode power transformer, shorted secondary diode and power ic. But in this article I'll explain to you another secret of electronic troubleshooting tips. I got frustrated as to where is the cause of power problem. Every time when i 'on' the power supply the fuse blow immediately (the fuse became black color and this show that there is a major short circuit in the power supply section). I have measured all the components in the power supply section and can't find the fault! What i do is i desoldered all the suspected components one by one and replaced with a known good parts. Finally I found the caused of the power supply problem. Guess what? It was the main power supply filter capacitor (220 microfarad 400 volt). After replacing the filter capacitor the power supply worked perfectly fine. I begin my detective work to find out why this particular capacitor can caused the fuse to blow even though I've already confirmed it to be working with my multimeters.

The meters that i used to measure the filter capacitor were analogue meter, digital capacitance meter and esr meters. In this article i will not fully explain about how to check capacitor or testing capacitor and how capacitor work. I believe most of you know how to check capacitors and also  generally using this type of meters. Measured with analog meter it showed the capacitor charging and discharging, with digital capacitor meter it showed around 220 microfarad and with esr meter it showed a very low esr reading! This proved that the capacitor breakdown when under full operating voltage. Then, how do i confirm that this filter capacitor is faulty? By using an analogue insulation meter. When i connect the bad capacitor to the meter and press the go button-it showed a very low resistance and this is the proved of short circuit between the plate when a high voltage is applied! There is nothing to do with bad electrolyte in the capacitor. A good capacitor will just indicate a charge and discharge in the insulation meter just like you are checking a capacitor using analog meter. In the market there is variety of insulation tester that you can buy. It has the range of 50volt, 100volt, 250volt, 500volt, 1000volt and even 5000volt! If you want to measure a capacitor of 100 microfarad 160v then you have to select 100volt. If you select 250volt, it will blow your capacitor that is under test. If you have the SENCORE TEST EQUIPMENT such as the sencore lc tester LC102 OR LC103, these tester have the capabilities of measuring any type of capacitors with four major test;

-testing for capacitance values
-checking for leakage in capacitor
-capable to measure equivalent series resistance (ESR) and
-Capacitor Dielectric absorption
It can check aluminum electrolytic capacitor, film capacitor,
ceramic, high voltage capacitor, mylar and etc.

Conclusion-Different capacitor manufacturer manufactured different type of quality of a capacitor. Perhaps the faulty capacitor that i encountered are from the lowest quality one. A capacitor failure when under full operating voltage is very uncommon. Using only the ESR meter can solve most of the electrolytic capacitor problem in the electronic circuit. If you do not have one, why not invest and it will pay back by itself in the shortest time. Happy Repairing!