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Power Supply Problem no output

Discussion in 'Troubleshooting and Repair' started by HajimeK, Apr 23, 2014.

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  1. HajimeK

    HajimeK

    9
    0
    Apr 23, 2014
    I have a problem..
    The thing is that..my transformer shows shorting behavior in circuit when it is soldered to the board but open when tested outside of the circuit..
    I have change all the active component on the board yet still to find the source of the shorting..
    The pin 1 and 2 are shorted on the board but when I take it out it no longer shorted..
    Is it how the transformer typical behaviour on board? or not?
    The problem with my smps is that there is voltage reading at the primary coil pin of the transformer but it still remains no output as I check it with the Voltmeter.
    Any Idea on how can I tackle this problem..
    The SMPS has 2 ouput which are 5 and 12 volt
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,480
    2,827
    Jan 21, 2010
    The pins marked 1 and 2 look like they might make contact with the edges of the pads on either side.

    The easiest solution is to cut these pins off. Another solution would be to trim the pads so they have at least a mm clearance from the unused pins.

    There may be other issues on the other side of the board that you haven't shown too.
     
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  3. HajimeK

    HajimeK

    9
    0
    Apr 23, 2014
    Thank you sir.
    Here is my assumption sir..
    The pins label are the secondary pins.
    As I just had the transformer Re-wind and the primary coil, all the pin show shorting characteristic as tested DMM.
    But the secondary coil only showed shorting characteristic at every 2 adjacent pins so I assume the transformer has 3 output voltage and assuming the coil has 3 distinguish coil winding turns.
    Anyway like u said..I plan on de-soldering all the component that I traced back to the secondary coil in order to find the source of the shorting and if failed..
    I will take u suggestion Sir..
    Thank you Sir to have taken time to help with the clarification.
     
  4. shrtrnd

    shrtrnd

    3,802
    507
    Jan 15, 2010
    Are you just taking static resistance readings with no power to the board?
    You do realize that a transformer IS 'shorted' coil windings, 'transforming' the voltage levels where the coils are tapped or as a function of the number of turns?
    ie; transformers ARE 'short circuits' to an ohmeter.
     
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  5. HajimeK

    HajimeK

    9
    0
    Apr 23, 2014
    Well thank you sir, and noted
    I understand sir that the transformer is shorted coil winding with the point is the tapped hence the different output value right?
    Anyway, does the point suppose to be shorted circuit on the board?
    Since I measure the ohm value is relatively 0 from the transformer to all the ground on the board. I have de-soldered all the active component.
    If I take the transformer out from the board..the only pin that is shorted; pin 1&2, pin 3&4 pin 5&6. at the secondary coil.
    but if its on the board, all the pins are shorted. If the coil is tapped to give different level of voltage; shouldn't it not short between pins.
    Together I attached some picture. I hope to fine the ampere value if can so that I can built one on my own hopefully
    Anyway, I am very thankful for ur response.Thank you very much.
     

    Attached Files:

  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,480
    2,827
    Jan 21, 2010
    OK, you need to indicate the pin numbering for us and tell us what the windings are supposed to be and what they're used for. Then we can give you some hints on how to test the board with the transformer removed.

    Have you applied power to the circuit with the new transformer yet?

    What is the minimum resistance range on your meter? Is it 200 ohms? Is it a 3 1/2 digit meter?
     
  7. shrtrnd

    shrtrnd

    3,802
    507
    Jan 15, 2010
    What *steve* said. But I am also trying to understand your understanding of what a transformer is.
    The coils (and there are at least 3 on your transformer), do not NEED to be tapped, to produce voltages other than what you input to the transformer.
    The simple process of winding the coils, 'transforms' the voltage levels at the output.
    The transformer coils read as 'shorts' (on an ohmeter) on a transformer by itself. When you install the transformer on the board, your coils are in series with whatever components are on the board.
    A transformer out of the board will not read the same resistance value when it is installed in the circuitry of the board, specifically because your ohmeter will be reading the transformer plus anything
    else the printed circuit board trace is tied to.
    The reason this is important is, as *steve* said, we wonder if you've actually powered-up the board to see if it's working with the replaced transformer.
    I believe that you are concerned about your ohmeter readings, and are being cautious about powering-up the board until you feel more confident about your unpowered ohmeter readings.
    You might want to Google information on how a transformer works, to get a better idea of what you're dealing with.
     
  8. HajimeK

    HajimeK

    9
    0
    Apr 23, 2014
    Thank you very much steve and you sir.
    I understand. And I have tested for both with power and with no power.
    And I found that the pin on the secondary coil pin, the ohmmeter reads 0 ohm directly when I measured from the pin to the ground.
    This time I am pretty confirm that the transformer is spoiled since I already de soldered all the components on the secondary coil side but yet the ohmmeter still reads 0 from the transformer pins to the ground.
    Anyway I ask the shop to properly re-coil the transformer.
    I will let you if anything.
     
  9. HajimeK

    HajimeK

    9
    0
    Apr 23, 2014
    Hello Sir and everyone..
    I have solved the problem or problems..
    Turned out the comparator(LM393) and the PWM IC is faulty..eventhough I tested it using multimeter its okay..but when I changed those 2 IC, the power supply got the output of +5, -5 and +12..
    Now I have learn that eventhough the primary pins of the transformer got reading on Multimeter, does not means that the primary side dont have any problem..

    anyway, thank you for the effort of helping me through this headache problem..THANK YOU VErY MUCH
     
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