There have been several members asking various questions regarding smp's, how to work on them safely, equipment required, (ring testers, esr meters, connecting oscilloscopes etc. With this in mind, and in no particular order are some of my experiences and recommendations based on over 50 years in electronics 22 of which where in servicing many different types of consumer electronics.
I am not saying that the advice I give is the only way, just that it worked well for my staff and myself and none of us died in the process of repairing thousands of devices.
Whether you want to repair a tv, computer power supply, use a wall wart to power your Arduino/Rasberry pi project or whatever I hope some of this will prove of use to you.
I will cover different aspects over a series of posts so that others can contribute, comment, and if need be, criticise.
So, first off I would like to show the usefulness of an inductor ring tester as this has cropped up lately on the forums.
When trying to diagnose a fault in a smp, the inductors are often overlooked as a possible cause. Maybe the resistance measurements look ok, maybe the inductance seems fine, but neither of these two tests are likely to show a shorted turn. Over 90% of the time, a ring test will.
Here are pictures of my original home made ring tester (Dick Smith original circuit) testing a small inductor. The first shows a healthy "ring" the second is with a loosely coupled single turn of wire acting as a shorted turn. See the difference between the two by the number of Led's lit and the waveforms on the scope.
Notice that the second waveform is highly damped, the ring tester Led's still show the initial ring but the scope really shows the effect!
This test alone could save you money and time, because it is all to easy to find a shorted switching transistor, diode, high esr capacitor etc., replace them and still have a problem or even blow up the new parts.
Next time I get a moment, I will show how to test for other faulty parts with ring tester, and explain what "ringing" actually is and how the tester works. You can of course just google the subjects yourself, there is a wealth of info available.
I am not saying that the advice I give is the only way, just that it worked well for my staff and myself and none of us died in the process of repairing thousands of devices.
Whether you want to repair a tv, computer power supply, use a wall wart to power your Arduino/Rasberry pi project or whatever I hope some of this will prove of use to you.
I will cover different aspects over a series of posts so that others can contribute, comment, and if need be, criticise.
So, first off I would like to show the usefulness of an inductor ring tester as this has cropped up lately on the forums.
When trying to diagnose a fault in a smp, the inductors are often overlooked as a possible cause. Maybe the resistance measurements look ok, maybe the inductance seems fine, but neither of these two tests are likely to show a shorted turn. Over 90% of the time, a ring test will.
Here are pictures of my original home made ring tester (Dick Smith original circuit) testing a small inductor. The first shows a healthy "ring" the second is with a loosely coupled single turn of wire acting as a shorted turn. See the difference between the two by the number of Led's lit and the waveforms on the scope.
Notice that the second waveform is highly damped, the ring tester Led's still show the initial ring but the scope really shows the effect!
This test alone could save you money and time, because it is all to easy to find a shorted switching transistor, diode, high esr capacitor etc., replace them and still have a problem or even blow up the new parts.
Next time I get a moment, I will show how to test for other faulty parts with ring tester, and explain what "ringing" actually is and how the tester works. You can of course just google the subjects yourself, there is a wealth of info available.