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12V, 5A LED Driver SMPS Repaired
One of my friends had informed me a few months back that one side of the Serial LED lights do not light up. When I went there and saw, it was fixed on the roof. He had two sets fit on the roof, one on each side. So, I had told him to get an electrician to remove the driver unit and bring it to me. Since getting an electrician to get such work done is almost impossible here, one has to wait until a major work arises.
So, this got delayed and finally, the unit was delivered to me yesterday. I opened the unit and just look at what I found inside and what caused the breakdown, and damages on the PCB:
The strange coincidence is that only the other day, an article was published in this forum about lizard causing a similar damage! As mentioned by me there, I had to once again witness the charred lizard and experience the nauseating rotten smell, though far less this time! Another coincidence is that the fuse had not only blown, but the glass cracked and shattered! This could be caused by the fuse wire developing resistance over a period of time and burning like the filament of an incandescent lamp before finally blowing off, which broke the glass!
I disposed of the dead lizard, cleaned the PCB and the bottom plate using Spirit thoroughly. Cleaned my hands with Hand Wash to prevent any contamination. On inspection of the PCB, I saw that positive rail was charred in one spot. Fuse was blown, as mentioned earlier and the Bridge Rectifier was dead short! The heat produced due to sudden rush of current, had created several dry solders in the primary section, and some of the soldered joints were like cast iron! Checked all the components in the primary, removing some of them like the Mosfet. Did not find anything wrong. Completed dry solder patch up. Connected a jumper in the positive rail and did a thorough cleaning of the PCB once again.
Connected a 60W bulb in place of the fuse and a mains cord, and tested the board. The bulb lit for a second and became dead, and the output was showing 12.11V, indicating that everything was well in the unit:
From the second photo at the beginning of this article, you will notice that the connections are dye stamped on the body; First two pins AC line in, third one Earth Pin, fourth and fifth are ground (-) and sixth and seventh are positive (+) for connecting the Serial LEDs. The power supply is rated for 12V, 5A.
So, connected 3.15A Fuse by soldering terminals at both ends. Rechecked the unit connecting a 12V 30W Automobile Bulb. It lit brightly:
Here is the unit fit along with the defective components:
Another ‘dirty’ job completed ‘neatly’!
This article was prepared for you by Parasuraman Subramanian from India. He is 66 years old and has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company.
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You may check on his previous repair article below: