Page 7 - Testing Electronic Components

2. Discharging Switch Mode Power Supply (SMPS) Capacitors

Most SMPS have a resistor to drain the charge in the main filter
capacitor. But some resistors may fail and the capacitor can hold this
charge even after you have turned off the equipment. This capacitor has a
range of about 150uf to 330uf at 400 working voltage.

Before you start to work on a power supply, always turn off the power
and discharge the capacitor. You can do this by placing a resistor across
the two legs of the capacitor. The resistor value can be around 2.2 to 4.7
kilo ohms 10watt. It takes only a few seconds to fully discharge a
capacitor. Double-check the capacitor with a voltmeter after every
discharge. I will cover more details in the capacitor topic on how to
discharge capacitors.

NOTE / WARNING:

Do not discharge capacitor with screwdriver because: -

i. It may melt the tip of the screwdriver.
ii. It will damage the capacitor and its terminal.
iii. If we are too near to the point of discharge, the heavy spark
generated may cause injury to our eyes.

3. Hot Ground Problem

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