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Precautions While Testing Capacitors

By on June 21, 2007

It is essential for your safety and to prevent damage to the device under test as well as your test equipment that large or high voltage capacitors be fully discharged before measurements are made. During the early days when i was still fresh in this electronic repair line, i’ve blown up few meters by the high voltage discharged from the Monitor filter capacitor. If you really want to safely¬† discharge the big filter capacitor in a switch mode power supply, please don’t use a screw driver as it may destroy the circuit board, melt the tips of the screw driver and even the debris may fly into your eyes. Just use a 100 watt light bulb to place across the leads of the capacitor and the charge will be gone in less than couples of seconds. As for me i prefer using a 10 watt 2.2 k ohm resistor to do the job.



  1. Robert Cunningham

    June 24, 2007 at 4:24 am

    Much better to use light bulb , as one can be sure it has discharged by observing short lamp glow.

  2. admin

    June 24, 2007 at 3:07 pm

    It is true what robert said but in some Monitor designs once switch off the voltage in the capacitor will quickly drop to around 50 to 60 volts and the glow hardly be seen in a 240v light bulb unless the equipment is running on a 110 volt! For beginners, no matter which methods you want to use, always double confirm with a voltmeter first after discharged before removing the filter cap.

  3. how to remove a capacitor

    January 18, 2011 at 1:53 am

    One of safest ways is to use a resistor that has jumpers connected to it.


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