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SMPS Problem

By on July 11, 2008

smps board

 smps board


I got these photos from one of my ERG members asked about how to fix this kind of problem. Here are the questions and the answers:

Since I’m still an amateur in this repairing field, most of the bad equipment that I try to repair are from the church’s. Now their fax has problem with no power at all, opening the case I saw the components surrounding the filter caps are darker, I can see it is because the filter caps leak. Now, the first thing to do is to clean the darker surface on top & bottom, but using Philips 390DCS/2 Degreaser Cleaner wouldn’t help. Do you know what cleaner fluid would help in this case. Having no schematics will add the difficulty to repair, so cleaning it is of the first importance. Could the ultrasonic cleaner help clean this darker area of the pcb? Do you often use this kind of cleaner? As you could see from the bottom side of pcb, the protecting green layer has taken off when I tried to clean it with tissue paper.

Yes the first thing is to clean up the area first. You can use a thinner solution where you can easily get it from local hardware shop. As for the ultrasonic cleaner, i have never use before thus i can’t give any comment about that.

Another question is the other board which has three telephone jack sockets has a small round component like fuse but with 3 legs identified as V2 on the board, what kind of component is that? Upon checking its resistance with digital meter, they are all open among the 3 legs, and the coding on its surface is 3P600 ss

It could be a varistor and the 3p600 could be the component can withstand up to 600 Volt.

Since the fluid leakage of e-caps is so corrosive, causing the resistor color coding, diode coding to fade that I can’t see the original type/code, do you think it is still serviceable?

If i’m the one handling this type of problem, i would only allocate half an hour for it. If it can’t be repaired i will just send back to customer. The reason is because the leaked electrolyte already eaten up some components and i’m afraid it may intermittently short circuit some of the adjacent track. Even if you can repair this type of problem, it may not last long due to that the board circuit and track already in bad shape.

Could I switch on any smps power supply safely without load, since the ouput socket has many pins and I don’t know which pin exactly is the output.

It depends on smps. some will work for a moment and shutdown, some will work and some will not have power at all at the output! Try measure the pins where the output electrolytic capacitors were located. Assuming you have seen one that have 1000uf 16 volt that means the voltage across the cap should have voltage somewhere between 8 to 12 Volt DC.

How to easily know which side of smps power transformer is the primary, because this one has both six pins on both sides.

Look for the + sign of the big filter cap and trace from there. It should have a path that lead to one of the transformer oin. Next look at the drain pin of power fet. Trace from there also and eventually it will goes to another pin of the transformer. So both pins is the primary winding.

Note: If you have other suggestions please do give comment-thansk!


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  1. deelip

    March 11, 2010 at 11:41 pm

    my smps is not working

  2. admin

    March 12, 2010 at 6:41 am


    May i know what have you checked?


  3. sayyid

    April 27, 2011 at 9:08 am

    respected jestin sir you are my teacher


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