Fantastic smps pulse width modulation (PWM) video by randyfromm. Playback and view it for few more times if you want to
be sure how this PWM works. It is very important to understand how a switch mode power supply work if you want to be a good electronic repairer.
As mentioned in my previous articles before that once you fully understand how to troubleshoot power section, other types of circuit is more or
less the same. If you are still no confidence in repairing power supply, i suggest that you get a junk monitor or any electronic equipment
and begin to dismantle all the components in it and compares the power supply section with any power supply schematic. Join power supply
forum and keep on learning.