PC SMPS schematics with IC 2003 and TL494

What would you do if you have got a couple broken Switch Mode Power Supplies, a screw driver and some curiosity!? Well obviously you would crack it open and try to figure it out. I have to admit, we would probably have opened them before they were even broke. That is exactly what I did.
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  • SMPS schematic using IC2003
  • SMPS schematic using IC KA7500
  • SMPS schematic using TL494 and LM339
  • Datasheets
  • Links
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    When I had a couple of them lying around, I cracked them open and after a few days, fixed some of them. It was actually much easier done than said. But one bad thing about SMPS repairs is that there aren’t any good resources out there on the web. (OK may be there are, but I failed to find some). That is why I decided to make a series of posts with my repair notes, schematics and stuff I have learned through opening those bricks. Being the first post, this is the schematic post. You can grab the schematics available on the net here. Please send me a link if you have found a new schematic and I will add it here.

    The Schematics

    There are two circuits commonly available for PC ATX SMPS.
    • Based on IC2003
    • Based on KA7500
    • Based on TL494 and  LM339
    KA7500 and TL494 are pin to pin compatible PWM controllers. There are only minimal differences in their specs. The major difference being for the TI one TL494 DTC offset voltage is 0.1V where as for KA7500 it is 1.2V.
    Thanks goes to : http://electro-tech.narod.ru

    PC SMPS using IC2003
    SMPS schmatic using IC2003. The cheap Chinese SMPS uses a circuit based on IC2003. The EMI filter and output filters are usually left out, and the components heavily underrated. The schematic is hard to find, not drawn by me.
    This schematic along with the low quality parts is normally seen in Mercury branded SMPS. I have 6 of those lying around. All with blown caps and no EMI filter. EMI filters are not much of a concerns usually for ratings below 350W. But a good engineer /designer will always add an EMI filter.
    The manufacturer has omitted this along with output filter coils to cut costs.
    SMPS-Inductor-repair-2003-schematic.JPG
    Here is an SMPS based on IC2003 after repairs. I found some inductors to add to the output filter, but couldn't find any for the EMI filter at input.
    SMPS schematic using IC2003
    SMPS schematic using IC KA7500
    ATX-SMPS based on TL494 and LM339
    The TL494 LM39 combination was the most widely used one till recently.
    Click on the images to enlarge. If you know anything about Switching Power supplies, the schematics are quiet obvious. They are simple. Include simple protections and have very few components.