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SMD Resistor Found Burnt  And Displaced In Enhance SMPS Model SFX-200D

By on July 20, 2021
atx sip module

repair atx power supply

This was one among the five SMPS brought from my hospital, where I work (now from home only). As the IT-Administrator had already cleaned the inside of this SMPS, it saved my time in doing it. I saw a lot of dry solders and one SMD capacitor lying loose besides the vertically fit PCB.

sip module in power supply repair

When I checked the cap next to it, following was the reading:

testing capacitor using smart tweezers

Anyhow, I replaced all the electrolytic capacitors on the board as a routine maintenance.

As I could not get the correct sized Tank Capacitors, I fit these two a little elevated for accommodation and tied it up to the heat zinc.

modify capacitor in power supply

The vertical board (control IC) had a lot of dry solder on the SMD components. So, I retouched all of them apart from cleaning and re-fixing the SMD resistor, which was found ok on testing.

(I had clear snap of this board in yet another work done earlier on a similar SMPS and confirmed the value of it from there)

repairing sip module

I retouched the board thoroughly with fresh solder and re-fixed the vertical PCB.

atx power supply repair

The SMPS worked very well on test. So fixed the cover and moved it for pick up by hospital staff.

Mission accomplished and satisfaction jumped into the collection bag with a bang! (LOL)

fixing atx power supply

Following components decided to call it a day and gave pose before moving out (LOL).

bad capacitors in power supply

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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14 Comments

  1. Paris Azis

    July 20, 2021 at 4:54 pm

    Dear Parasuraman,

    I don’t mean to be rude, I hope you can understand me, but taking into account the rule which says that “topographically the electrolytic capacitors should not be installed near heat sources”, the idea of supporting the bulk caps on that heatsink is completely wrong. Especially the one which touches the heatsink will suffer badly, no matter the existence of the cooling fan.
    These replacement caps should have at least the same or even smaller diameter than that of the originals either for proper operation of the system, or for its improvement...

    Likes(3)Dislikes(0)
    • Parasuraman S

      July 21, 2021 at 2:15 pm

      There is no question of 'rudeness'! You have every right and freedom to express your opinions, which I welcome very much! You have a valid point there. The caps are not closely touching the heat zinc. It is only tied to the heat zinc for holding it firm. By the way, another similar repair done by me, by mounting the caps on top of the heat zinc, is still working for many years now in the hospital. These caps are capable of withstanding upto 85 degree centrigrade. Let us hope it would work for a longer time! Many thanks for your expert comments!

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  2. A van Bemmelen

    July 20, 2021 at 7:52 pm

    The fact that dear Parasuraman wasn't able to find the right smaller size tank capacitors again after replacing so many e-caps already before, probably says something about the bad thinner e-caps that deteriorate sooner in these smps units. Opposed to the bigger in diameter tank caps that are the only ones still available?

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    • Paris Azis

      July 20, 2021 at 9:15 pm

      No, Albert. Their deterioration doesn’t depend upon their diameter, but on their construction (i.e. quality) in general. On the other hand, they have been replaced “as a routine maintenance “. I think that a) if, perhaps, the original caps of this stage were in good health, they shouldn’t be replaced, at least until proper replacements were available and b) this replacement, with these bigger ones should be done somehow differently, let’s say should be shifted to the right, using new drilled holes on the PCB in order for them to be fitted solidly there and at a safe distance from the heatsink that they now touch. I believe that there were better options than the chosen one anyway. Usually these power supplies have enough space for such modifications.

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      • Parasuraman S

        July 21, 2021 at 2:19 pm

        Many thanks for your expert comments! There is space constraint in ATX SMPS. We cannot find another place for fixing these. Even for accommodating slightly larger caps, we need to shift the surface mounted components to underneath. That is the situation!

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        • Paris Azis

          July 21, 2021 at 4:26 pm

          I definitely understand your point Parasuraman, as I have faced the same problem many times up to this day.
          Simply this type modification (which sometimes I am also forced to use) is for me “the desperate man’s choice” and by that I mean that I would have come to a similar solution only after having been left without any other alternative.
          For sure, if the original caps were within their tolerances in terms of capacitance and ESR, I would prefer not to replace them until I had the proper ones at hand.
          Anyway, the point is always to bring a dead equipment back in life and under this light the repair (all what had to be done) is done.
          Just for better understanding of my point of view: if one of my technicians (in the telecom company I’ve been working in the past) would do a repair in this way, the Quality Assurance department would had him immediately fired, no matter any of his claims for a successful repair. And I admit that this thought affects my view on such repairs...

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          • Parasuraman S

            July 22, 2021 at 1:08 pm

            Yes, this type of repair is not professionally acceptable at all! I am fully aware of that too!

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    • Parasuraman S

      July 21, 2021 at 2:17 pm

      You are right! We have no choice except to use what is available in the market! Many thanks for your expert comments!

      Likes(1)Dislikes(1)
  3. Waleed Rishmawi

    July 23, 2021 at 1:58 pm

    yes attaching capacitor to a heat sink might be wrong but I appreciate the fact you are accepting the comments even when they are not in your favour is pure professionalism and I respect that.
    my humble opinion there is no need to replace the capacitors when they are not faulty replace only what is needed to be replaced. have a blessed day my friend.

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    • Parasuraman S

      July 23, 2021 at 3:40 pm

      Many thanks! Unless we accept others freedom and rights, we cannot have our own! Accept, admit and adjust (and if necessary alter our attitude) are three watch words to live peacefully in a complex world! In our life everyone and everything you see (or interact) has something or other to teach us. All are professors in their own way. So, let us keep our eyes and ears open and sharpen our intellect to absorb what we can learn as much as possible! I follow this as my motto!

      I value your opinion about not replacing all the caps. I do it as a preventive whenever these are quite old enough to replace. Fresh caps from fresh batches will go well when put together and there might not be any impedance imbalance is what I strongly believe from my experiences!

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      • Paris Azis

        July 24, 2021 at 4:27 am

        This kind of thinking deserves only respect Parasuraman! And you sincerely have mine, as "you've read my mind" in your 1st paragraph. My thinking is in line with yours.
        Criticism can be both: destructive to a relationship (if it is baseless, dishonest and not sincere) or constructive (when there is a basis for a honest and sincere discussion and exchange of ideas, when logic arguments are present). It all depends upon the intention of both sides and it needs "cool blood" in order to interpret that correctly. Unfortunately, in many cases, this is interpreted as a personal attack without any attempt of analysing the attitude of "the other side", that is, to question oneself "why is he saying what he says" or "do his arguments stand on a solid base". And here exactly, the "cold blood" should be talking in order to put out the correct answers to these questions and save the otherwise destroyed relationships...!!
        As for your second paragraph, there is no problem with impedance imbalance with these capacitors under discussion, as these two high value resistors, which are always present, being connected each one to each cap, serve exactly this purpose. To equalise any asymmetrical voltage distribution between the two (in series connected) capacitors (:half bridge topology), which is due to unequal leakage currents within each one of them (a fact which is always there even when these caps belong to the same production batch). The restriction only says "do not use caps with different capacitances and voltages". So, you shouldn't bother about that at all. You only need "to kep the rule" and by every chance verify that the values of these two resistors are equal, providing voltage symmetry.

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        • Parasuraman Subramanian

          July 24, 2021 at 9:25 am

          Many thanks dear!

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  4. Yogesh Panchal

    July 28, 2021 at 4:10 pm

    Sir, Now all future repair is depend on the line Accept, Admit and Adjust because of new manufacturing trend like material without marking........thanks! God still they are Marking Value On electrolytic Capacitors...................

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    • Parasuraman S

      July 31, 2021 at 9:48 pm

      Yes, very true Yogesh! Many thanks for your observations!

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