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What is making a squealing noise on this plug in?

Robmac

Nov 12, 2017
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Nov 12, 2017
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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
 
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Minder

Apr 24, 2015
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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..
 

duke37

Jan 9, 2011
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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

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Sep 5, 2009
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It does not look like a SMPS

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

so I would guess the transformer is vibrating due to the load.

and yes, that is still the logical conclusion

but note he said it's squealing

SMPS transformers squeal, linear transformers buzz/vibrate
 

Robmac

Nov 12, 2017
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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!
 

Minder

Apr 24, 2015
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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.
 

davenn

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Sep 5, 2009
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also the primary connections appear to be fed right off the AC.

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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