Two Computers SMPS Saved From E-Waste!
I had about four of these Computer SMPS lying around with me, couple of which was taken out of my PC from time to time. One or two might be from a ‘getting-rid-off’ campaign done by one of my brothers. Anyhow these have been lying unused for almost 7 years. All of them were reconditioned and kept as a standby. Since the PC was given to my grand children for their school use, these SMPS got stranded, as now I am using a laptop gifted by my elder son.
So I gifted all the four SMPS to the hospital and requested the IT Administrator to try it out before fitting it in any computer as a replacement. He reported that two of the SMPSs fumed when connected! That’s how these two landed back on my service desk in the home. When I opened one of them, I saw a cap burst in the primary.
The ESRs of all other caps were good and therefore I did only replacing these two caps and doing the retouch of the board. Also cleaned the board thoroughly and it shined like new. It is my routine to check the retouch of the board and inspect it for any man made shorts, which I do using my digital microscope:
After that when I applied power and found everything was working, I fixed the cover and gave a 12V, 25W automobile bulb as a load and allowed it to run for a few minutes. It was working fine.
Opened the second one and found a 1000/10V cap burst. Since the fuse was intact and the ring test on the primary of the SMPS showed healthy, I knew that could only be the problem. Checked the ESRs of the caps and found these way out.
The board had already undergone dry solder patch up. So I removed the caps one by one and checked. Look at my findings:
The 1000/10V cap you see in the left above is not the bulgy one. The reading of a new cap is given on the right for a reference. After replacing all the caps, I applied power and found the output was ok.
But the fan did not rotate! Checked the voltages at the pins and found these to be ok.
So, replaced the fan also. After ensuring everything was working fine, fit the cover back and gave a load of the automobile bulb like before and allowed it to run for a few minutes.
Missions accomplished satisfactorily and it did a double jump to the collection bag!
Special notes: (1) I believe the technician fraternity owns the responsibility to control the e-waste and protect the environment (2) The methods employed in troubleshooting described in this article are very ideal for adaptations, like close inspection of a dry solder patch up done. (3) My interest was aroused in SMPS troubleshooting after reading Jestine Yong’s internationally famous book. That’s a great book one must have and read and refer to it too quite often. (4) It is always a thrilling experience to set right a defective device and no reward can ever be as befitting as the satisfaction and boost we get after accomplishing the results!
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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19 Comments
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ANIL KUMAR V K
April 2, 2022 at 1:03 pm
Excellent sir
Parasuraman S
April 2, 2022 at 8:57 pm
Many thanks!
Albert van Bemmelen
April 2, 2022 at 1:56 pm
Excellent repair as usual! Maybe these Power supply e-caps end in a shorter life span because they endure high inrush currents all the time?
Paris Azis
April 2, 2022 at 3:01 pm
No, Albert. These caps are of very low quality. This is the main cause these P.S.Us fail.
On the other hand, the inrush current happens only once, when the unit is powered. After that, it remains permanently powered in standby mode.
During this mode, only the standby subunit within it is active. This means that the primary side is permanently switched on (although working at low load level) which shortens the life of the primary side caps.
Their secondary counterparts suffer worse when the unit is turned on because of the heavy loads they see, plus the many harmonics (developed by the switching frequency) which they have to suppress...
Needless to say that this unit has no protection circuits at all. Even the common noise filter at the input is missing...
Therefore the first overvoltage of the mains will surely kill it...
Parasuraman S
April 2, 2022 at 5:24 pm
Many thanks for the detailed information and analysis of the ATX PS circuits. Very valuable, indeed!
Parasuraman S
April 2, 2022 at 3:33 pm
Could be. Many thanks for your comments!
Paris Azis
April 2, 2022 at 2:39 pm
This power supply is the worst I have ever seen! Although it has a relatively good circuit design, the quality of its materials is very bad, especially when it comes to its electrolytic capacitors. I have repaired too many of them when working at our Public Power Corporation and I can say that I have practically seen all the possible theoretical failures described in textbooks in their circuits...and replaced some hundreds of these unforgettable green lousy caps... In some of these cases the cost of buying the needed spare parts was approaching their buying price (25€ at that time) rendering their repair worthless...
Good job Parasuraman!
Parasuraman S
April 2, 2022 at 5:25 pm
Many thanks, dear for your valuable comments and experiences!
Babu M S
April 2, 2022 at 10:51 pm
Very good repair work and special note sir.May I know what is the cleaning agent your using to clean pcb boards.
Parasuraman Subramanian
April 3, 2022 at 9:55 pm
I use IPA (Isoprophile Alcohol). Many thanks for your comments!
Anwar Shiekh
April 3, 2022 at 4:43 am
Great repair: pity manufacturers don't use capacitors that outlast the warrantee period.
Parasuraman Subramanian
April 3, 2022 at 9:56 pm
That's to make more money, obviously! Many thanks for your comments!
Mark
April 3, 2022 at 11:09 am
Thanks Parasuraman,
A good repair and a detailed article.
Parasuraman Subramanian
April 3, 2022 at 9:57 pm
Many thanks, dear!
Yogesh Panchal
April 4, 2022 at 2:41 pm
Good Job! Sir,
Parasuraman S
April 4, 2022 at 7:16 pm
Many thanks for your comments!
Waleed Rishmawi
April 4, 2022 at 3:52 pm
thanks for sharing such a repair. I never attempted to do such repair due to the fact that they are so cheap in my home town to purchase. I thank you for shedding the light on such repair and have a blessed day
Parasuraman S
April 4, 2022 at 7:19 pm
Yes, it is cheap here too. But my service is free for the hospital and most of the times I do not even charge for the components replaced. We had to buy an SMPS of computer very rarely because of this. Therefore, it works out to be a benefit. Additionally, I have noticed that the reworked SMPS lasts longer than the new one! Many thanks for your comments!
jai Etwaroo
May 8, 2022 at 8:29 am
Nice job buddy.