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How To Quite Down A SMPS Transformer

By on May 27, 2008


Hi Jestine,

I have checked the SMPS report, which was very interesting because I’ve been recently repairing one ATX computer power supply. The problem with this supply is that it keeps “whistling” at high frequencies when it’s loaded. The sound is coming from the high frequency power transformer and it only stops, if I push it down really hard with a pencil. I have checked all the elements, capacitors seem fine, they aren’t ideal (there is always some leakage), but they should be fine. Controlling circuit is ok, standby voltage too, output voltages are ok (no ripple), which I checked with an oscilloscope. A friend told me, that the problem could be transformer itself, but I cannot find a replacement transformer, so this PS unit is basically beyond repair, unless someone was to fix the transformer or I found the exact same PSU.

I have also checked your capacitor checking video, which was quite interesting. Unfortunately my multimeter is about 10-15 years old and it only supports up to 20 uF, so I have to use ohm-meter to see if the capacitor charges and where it stops charging (leakage).

Thanks for writing those interesting reports, electronic repairing can be fun, especially as a hobby.

Best regards,


Hi Karl,
Try dip the whole transformer into shellac for about  5 to 10 minutes and then let it dry for at least 24 hours before you fix it back to the power supply. I had quite down some of the transformer but again if there is component problem especially an open ceramic capacitor nearby the transformer (primary side) it could cause high frequency noise too! As for checking electrolytic capacitor the best is still the ESR meter where you can get it HERE.

Best Regards,
Jestine Yong



  1. Danny F

    February 13, 2011 at 5:30 pm

    Hi Jestine,

    I need to purchase some shellac or alternative.
    The website below sell it, but they call it Shellac Polish / Sealer.

    Do you think this is suitable for dipping transformers/coils?


  2. admin

    February 14, 2011 at 3:56 am

    HI Danny,

    Yes it can be used.


  3. Danny F

    February 14, 2011 at 4:13 pm

    Thanks Jestine.

  4. jun

    April 6, 2011 at 10:30 pm

    my tv have a sound but no pictures, its totally black. hope you can help me. thank you

  5. admin

    April 7, 2011 at 1:28 am

    Hi Jun,

    Any output voltages from the power supply?



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