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About Switch Mode Power Transformer (SMPT)

By on November 10, 2007

 switch mode power transformer

Do you know that Switch Mode Power Transformer (SMPT) is very robust and seldom fail? If it fail, most of the time is the primary winding that go bad and you need a coil tester to test it. Many techs called it as ringing the transformer. If the primary winding is shorted , it would cause the fuse to blow or many times it also blown up all the related components in the power supply section. Due to this, i always ring the SMPT first before i start testing and checking on other components. This can save your time as a shorted transformer is not easily can be found in the market.

It depends on the transformer designs, some motor rewinder may successfully rewind the SMPT and some may reject it due to the complicated small windings in the SMPT. There is one model of HP 17″ Monitor the SMPT have high failure rate. The cause of the problem was a dry joints in the flyback transformer pin causing the HOT to go shorted. And this burnt the B+ coil, B+ FET and eventually burned the SMPT primary winding too. I was surprised that the fuse didn’t blow. Replacing only the bad components solved the problem. Make sure you have a coil tester to do the job in measuring the primary winding of switch mode power transformer.



  1. Nadeem

    April 9, 2011 at 10:02 pm

    Dear Jestine,

    Kindly advice where I can find a " coil testr " to check SMPT.

    Nadeem Sabir

  2. admin

    April 10, 2011 at 3:18 pm

    HI Nadeem,

    Please visit



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