Yet Another CCTV SMPS Found With Tank Capacitor Burst
This adaptor of a CCTV is one among the five brought to me by a service provider. On opening, I found the tank capacitor bulged:
On a ring test, the SMPS transformer showed healthy. This was also an indication that there are not likely to be any shorts in the primary or secondary. I replaced the capacitor along with the other electrolytic caps to make it a total pep up.
Then I applied power and checked the wave form in my oscilloscope, keeping the probe on top of the SMPS and connecting the ground wire to the hot ground. Got a very healthy wave form with a >12V output:
Mission easily accomplished with an addition of satisfaction to the collection.
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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Multivits
June 17, 2023 at 7:55 am
Hi Parasuraman, I'm not an expert on this topic but when I have tried to connect my oscilloscope ground to the hot ground of the SMPS being tested it trips the RCD. Did you use an isolating transformer? If so could you show how an isolating transform deals with the earth \ ground connection, as I may have another attempt at repairing SMTP's and get an isolation transformer
Parasuraman S
June 17, 2023 at 9:39 am
If you are using an oscilloscope, especially the CRT type, use an isolation transformer for the service table or the device that is getting connected. The earth of the oscilloscope is the ground point of mains. That's why the MCB or ELCB trips, as either the line or neutral gets directly connected to the ground. The earth leakage detector then trips. Always connect the oscilloscope directly to the mains. I have learnt this from web and personal experience. The user manual of oscilloscope always mentions this. It is not advisable to use an isolation transformer for the scope, as the secondary floats. Hope this helps!
Albert van Bemmelen
June 17, 2023 at 1:08 pm
Apparently it now becomes a habit for everyone to use an oscilloscope to afterwards also check the smps waveform. Although we already easily established that the output voltage was correct and the light bulb trick showed that no short circuit was detected. I suppose that checking the smps waveform is more useful if the power adapter for some unknown reason still doesn't work as expected?
Parasuraman S
June 17, 2023 at 2:43 pm
Many thanks for your expert comments and observations. Yes, checking on an oscilloscope is very useful when no output comes. But occasionally we do check the wave form to know whether it is healthy enough as a precautionary preventive!
Waleed Rishmawi
June 17, 2023 at 4:48 pm
ah, the joy of replacing capacitors...lol. thanks for sharing your repair story. I do not use oscilloscope at all. I have a CRT one and one that connects to my laptop but I never bothered to use unless i have to. of course it is just any openion. have a blessed day my friend.
Parasuraman S
June 17, 2023 at 9:09 pm
Yes, dear! I too owned an oscilloscope only in a very later state of my hobbyist life. I could not afford to invest in one until I reached a comfortable position. But in SMPS repair, how the pulse is generated is an important and easy check to determine the type of problem we have to resolve. Moreover, in my audio repair, perfecting the output signals in both channels can be made possible by use of an oscilloscope. The trouble shooting on an audio device using a dual trace oscilloscope to know the difference between the signals at various stereo stages, is very important. Many thanks for your comments and observations.
Waleed Rishmawi
June 19, 2023 at 6:07 pm
totally understand the concept but what I meant in my kind of repair it is not needed that much. have a blessed day
Parasuraman S
June 23, 2023 at 8:02 am
Of-course, dear! Thanks!
Anwar Yunas Shiekh
June 17, 2023 at 9:24 pm
I am used to it being called a bulk capacitor.
Parasuraman S
June 18, 2023 at 9:48 am
Oh! I see! I have never heard of it! Thanks!
Sarath Rane
June 19, 2023 at 9:27 am
We used to call it "Reservoir capacitor"
Parasuraman S
June 23, 2023 at 8:03 am
Yes, I have heard it!
Yogesh Panchal
June 25, 2023 at 12:26 am
Good fix! sir
Parasuraman S
June 26, 2023 at 9:33 am
Thanks, Yogesh!