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What is making a squealing noise on this plug in?

Discussion in 'General Electronics Discussion' started by Robmac, Nov 12, 2017.

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  1. Robmac

    Robmac

    2
    2
    Nov 12, 2017
    Hi there,

    I have a Christmas village decoration and the plug in box makes a high pitched squealing in time with the lights whenever it is switched on... am I able to remove a piece to stop it? If so, which piece?

    Thanks

    psu1.jpg

    psu2.jpg

    lights1.jpg
     
    Last edited by a moderator: Nov 12, 2017
  2. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    It does not look like a SMPS so I would guess the transformer is vibrating due to the load.
    You could try taking the yellow tape off and spray or brush shellac on it.
    If you place a finger on the top of it can you feel any vibrations?
    M..
     
  3. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    It may be a SMPS with Q1 as the switching transistor.
    If D1 to D4 form a bridge rectifier connected to the mains, then it is a SMPS.

    Is it my imagination that the electrolytic capacitors have domed tops? Faulty caps could overload the transformer.
     
    davenn likes this.
  4. davenn

    davenn Moderator

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    1,945
    Sep 5, 2009
    yes it does look like one ;)

    As Duke said, the transistor gives it away :)

    guaranteed to be a switching chip and some other SMD components on the bottom side of the board

    and yes, that is still the logical conclusion

    but note he said it's squealing

    SMPS transformers squeal, linear transformers buzz/vibrate
     
  5. Robmac

    Robmac

    2
    2
    Nov 12, 2017
    Update: I covered the transformer in shellac and it minimised the squealing enough to make it inaudible unless you are right next to it.

    That should work for now haha.

    Thanks all!
     
    davenn and Minder like this.
  6. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    Your welcome.
    Check to see if the transformer is made up of steel laminations, if so it is a linear supply, also the primary connections appear to be fed right off the AC.
    M.
     
  7. davenn

    davenn Moderator

    13,812
    1,945
    Sep 5, 2009
    ohhhh golly gosh

    think you need some new glasses ;) ..... don't you see the 4 rectifier diodes beside the AC input pins
     
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