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14 Bad Components Found In Intex SMPS Model Smart IT-2045S+ (Unbelievable)
This SMPS was brought to me with a complaint that a loud noise was heard and it has become dead. On opening, I could see a lot of black dust all over in so thick a form; I took it to an open area for cleaning it.
As the computer was in use in an area, which was generally damp, the dust inside had got stuck inside! After thorough cleaning by brushing and rubbing using various brushes, including bottle brush, I could bring it to a tolerable condition. The dust on the PCB side was sticky. On one spot, where the two tank capacitors are located, I could see the PCB tracks had burst and burning marks on the bottom plate. The Fuse was found cracked. Unfortunately, I could not use my camera at these stages, as my hand was very dirty.
The second picture is a cropped image after I had completed the cleaning. Due to moisture, this portion had shorted to the bottom plate and that is why, the fuse was blown.
After another round of cleaning using PCB cleaning solutions, I checked the components in the primary and secondary. Found the Bridge rectifier short. When I was looking for a replacement from my stock of components, I could see the following:
The first image is of the defective bridge rectifier. The second image is of the BRs in stock. I was surprised to see that the cutting on the top, which is an indication of + side of the bridge, was on the – side in one of them! Checked and confirmed that the positive marking on it was correct and not the cutting. Unless we are very watchful and check all these aspects, we are likely to get into more troubles! As the defective rectifier was of 700V and 5A, I got an exact replacement from the market and soldered it. On checking the ESR and values of electrolytic capacitors, especially the tank capacitor, it was found to be out of range. So, replaced all of them, (except the two tank capacitors that will be explained separately later in the article), which is my thrilling and favorite work! I normally write down the capacitor number on the PCB and its value on a piece of paper and keep it safe. This method will enable us to do the removing work at a stretch.
Noticed that the DC wires – black for ground, red for +5V, orange for +3.3V, yellow for +12V, blue for -12V, and grey, green, violet and white from the IC for power on function and front panel – were almost all had collected rust at its base on the PCB side and were holding only on a few strands! So, removed them from the PCB marking the colours of the wires from the IC side. All other wires had the marking of volts printed on the PCB. I also saw a few rust formations on components.
Cleaned up the rust formations with IPA, and found that the rust is only on the outer side and it has not caused any damage of concern. Did a thorough dry solder patching up.
Now, about replacing the two tank capacitors. The value of these were 330uF/280V and were of small sizes. But exact replacement was not available in the market. So, I had to go for the 330uF/250V caps, which were slightly larger in size too. But for placing them on the PCB, I had to move out the bridge rectifier and fix it elsewhere, push the fuse slightly to a side, fix the bleeder resistor at the bottom of the PCB and then drill holes for wiring the bridge rectifier. Provided proper insulation using heat shrink sleeves, pasted the bridge rectifier on the heat zinc and further tied it to ensure that it does not get detached from the bond and fall off due to heat. One of the tank capacitors was fit tilting it to the other side, keeping one pole at the same spot, and wiring the other end to the appropriate place on the PCB. In such SMPS circuits, the two tank capacitors are connected in series, one will take the negative voltage and another will take the positive voltage. The other ends of the caps are joined in one place. I enjoyed doing all these circuses on this SMPS!
Whenever we do such innovative modifications in a circuit, it gives us a real thrill and excitement! In the second picture, the snap is before I provided patch up wiring of the cracked tracks. Though there was some portion of the track still intact, I joined them using cut leads of components to ensure that there was proper enough contact.
Connected the SMPS Fan temporarily, shorted the green wire to ground, and powered it on through a series bulb. It worked very well!
Fit it back on the box and covered it up, as the final stage of completion of a thoroughly enjoying service work! You can also see the defective components sadly posing for a snap, like culprits caught by police! (LOL) Is there a similarity in our real life? These components failed due to external circumstances; so are the people who are influenced to do bad things mostly due to living conditions! Humans have thinking power, whereas these are depending on the design and tolerance limits. But are we too not designed and programmed to be what we are? Well, a point to ponder over!
Another exciting job added to my growing list, which also provided some spiritual thinking!
This article was prepared for you by Parasuraman Subramanian from India. He is 69 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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