LOPT Tester Checked On Transformer’s Primary Winding In Power Supply
This 24V power supply was dead when it was brought to my shop. This is a power supply for a mini printer that this customer uses in this shop. Recently, this customer had power issues at his shop that caused a lot of damage to his electrical and electronic devices.
It was a normal power supply and I could not see any physical damage to it on either side of the board.
I powered up the devices and checked for voltages at the main capacitor but there were none whatsoever.
From the capacitor back to the bridge rectifier, when testing it with my multi meter set to diode, I came to a conclusion that it was shorted. And from a logical point of view, if that part is shorted, I am sure the fuse is open as well.
I de soldered these part off board and did further tests on them and it was confirmed that the bridge rectifier was shorted and the fuse was indeed open.
With my LOPT/FBT tester, I did more testing to make sure all was well. That is done by locating one of the probes on the Mosfet and the other probe on the main capacitor pin. According to the lights I was getting on my meter, everything in that area is ok.
I replaced the bridge rectifier and soldered it on board but I did not add the fuse yet. To make sure there is no more shorted component, I added a light bulb to the two pins of the fuse. Now, if the light bulb came on or stayed off, it means all is well to add the fuse but if the light bulb came on and stayed brightly on, we still have shorted components in that charger.
In my case, the light bulb stayed off and the charger LED light came on indicating all is well and that it is safe to put the fuse back on board, put the charger together and then give it to the customer.
Mission Accomplished.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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Jestine Yong works as an Electronics Repair Lecturer in Kuala Lumpur Malaysia and his training website is http://www.NoahtechElectronicsTraining.com. You can check out his repair blog at http://www.JestineYong.com
13 comments on “LOPT Tester Checked On Transformer’s Primary Winding In Power Supply”
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It is always a pleasure to service such small devices and I really love it! A professional solution there! Thanks for sharing!
Parasuraman: I thank you my friend. Have a blessed day
Strange hearing about so many power issues that cause a lot of damage to electrical and electronic devices in your country. We never have those except when lightning strikes into the to the television cable or the power lines connected devices. Or very rare power line outages that never take very long and therefore normally never cause any damage.
Albert: winter time this happens a lot especially when we loose power due to heavy wind ,rain and sometimes snow. When power is restored it goes up to almost 300 AC volt for few seconds before it drops down back to 220 AC volts. That is why in my house and shop I trip the earth leakage manually and I engage it back five minutes after the power is restored in my area. Have a blessed day
good job, were can i get a LOPT/FBT tester?
Hector: http://www.electronicrepairguide.com/blue-ring-tester.html
Different brand but same kind of job.
Great article especially getting tips on how to do certain tests like the lopt tester on the pins of main cap and drain of mosfet to look for shorts, great article, thanks.
Marco: I am glad you liked it. This process will save you time. Have a blessed day
Thanks for the article.Ilearnt a lot from it. Please keep it up.
Thanks Walleed for the article. Its the second or third time I keep referring to because it so nice to read all your articles, keep the good work. I hope you and your family is always safe of this covid-19.
Hi my friend, I am talking about 16 and 36 volt hp power supply with burnt fuse, even with replacing the burnt fuse, the power supply is still not on. I asked you for help on how to fix the problem. Solve the problem, thank you for your help
We don’t know what your level of training is so here’s some recommendations.You can learn by going to the links on this site under smps repair, other basic e-books are well worth the cost. Thanks to Jestine for this excellent site for technicians.
Mr. Waleed, thanks very much for the articles. I always get inspired by them.
Keep it up!