Restored A CCTV Power Supply With A Perfect Output
This Power Supply Adaptor was brought to me with the complaint that it was dead. This was one among the five power supplies brought by the guy who was in the business of CCTV installations.
He has done it in my home too. All of them were reported to be dead. On opening, I observed a bulgy capacitor, value of which was 120uF/400V.
As the burst capacitor had leaked the electrolyte all around, I cleaned the inside and outside very thoroughly using IPA as these can create problems. Then removed the cap. The fuse was found open. The bridge rectifier was also found short! After removing these, I did a ring test on the primary of SMPS transformer and found a healthy indication (i.e., all LEDs lit).
As the size of the 120uF cap that I had was larger, I used two 68uF/450V in parallel and fixed it on the board after drilling holes in a vacant place and wiring it on the other side taking care to provide heat shrink sleeves to avoid any arcing. Then replaced the 330uF/50V caps with 63V Caps in the secondary side and the 100uF/25V in the primary, while replacing the other defective components. Retouched the board wherever I found dry solder.
After this, I applied the power through a series bulb and got an output voltage reading of around 51VDC. I checked the wave form in my oscilloscope, by connecting the ground wire to hot section and just keeping the probe on top of the SMPS transformer, as advised by Jestine Yong in his world famous SMPS repair book.
The replacement of the 100uF/25V was important, because of its role in shaping the pulse. Mission accomplished and satisfaction found its way to the collection bag without any assistance from the Google GPS guiding lady! (LOL) Let us have a look at the concluding pictures:
This article was prepared for you by Parasuraman Subramanian from India. He is 72 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous article on Shorted Cap In Scalar Board Caused No Display In SONY LED TV KLV-29P423D
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Andrew F. Ali
June 3, 2023 at 9:47 am
Very good.
Parasuraman S
June 3, 2023 at 2:50 pm
Many thanks!
Albert van Bemmelen
June 3, 2023 at 3:14 pm
It was likely the burst 400V 120uF cap that destroyed the fuse and bridge rectifier in the primary of these power supplies. The cap voltage better at least should have been chosen higher like 460V as they are in most good designed power adapters. And the replacement 450V caps are also much better compared to the previous max 400V e-cap type.
Parasuraman S
June 3, 2023 at 6:06 pm
Many thanks for your expert observation and comments, dear!
A.D.Rana
June 5, 2023 at 11:30 am
Sir,
I have similar adopter, I have replaced the Main Capacitor but still do not get output.
DC Volatage acreoss capacitor 321 V DC.
OB2201 PWM IC get 12 V DC supply for starting but still firing of MOSFET Not takes place.
Drain Source voltage same as Capacitor Voltage.
Pl Guide me for the same.
From,
A.D.Rana
Gujarat India.
Parasuraman S
June 5, 2023 at 10:16 pm
I suggest you buy Jestine Yong's SMPS REPAIR book as soon as possible. I learnt and took great interest only after reading his excellent book. It is worth it! There are many reasons for not switch-on. You need to check secondary components for any short. Check whether the output comes and then goes off. Then secondary could be the problem. Then, opto-coupler, TL431, resistors that give feedback etc. should be checked. Running DC diode also can create problems. Change the small value capacitor in the primary. Check each and every component, if possible, by removing one end. Look for any dry solder. All the best. Many thanks for your comments and query!
Andy
June 3, 2023 at 3:50 pm
I prefer repairs to look like stock, and avoid modifications; but that's just me.
Parasuraman S
June 4, 2023 at 7:34 am
Well, I agree with you and I try to do it that way as far as possible! Many thanks for your comments!
Yogesh Panchal
June 3, 2023 at 6:00 pm
Good Fix! Sir
Parasuraman S
June 4, 2023 at 7:34 am
Many thanks, dear!
Mark
June 3, 2023 at 7:05 pm
Well done Parasuraman!
Parasuraman S
June 4, 2023 at 7:35 am
Thanks, dear!
Waleed Rishmawi
June 7, 2023 at 4:11 pm
Ah the joy of replacing the capacitors is just amazing…lol
Good job on the repair, I always enjoy such repairs. Have a blessed day
Parasuraman S
June 8, 2023 at 8:30 am
Ha! Ha! Many thanks, dear friend!