High pitch noise PS board

[rodrigopires]

Hello eneryone,

I have a Nodor kitchen extractor that is making a humming noise (I mesured around 6.4 to 6.8 kHz) all the time, even when nothing is on so it leads me to believe that its coming from the logics power supply. And the sound gets worse if I turn on the lights...

I toucht every component (with a plastic stick) and could not find the source of the sound (also no Change um sound) so no loose cores... Also did nota see any bad caps (aparently).

What could bem causing this?

Video: https://youtu.be/p3Zme8-ApkQ

[srb1954]

Hello eneryone,

I have a Nodor kitchen extractor that is making a humming noise (I mesured around 6.4 to 6.8 kHz) all the time, even when nothing is on so it leads me to believe that its coming from the logics power supply. And the sound gets worse if I turn on the lights...

I toucht every component (with a plastic stick) and could not find the source of the sound (also no Change um sound) so no loose cores... Also did nota see any bad caps (aparently).

What could bem causing this?

Video: https://youtu.be/p3Zme8-ApkQ

Have you got a scope so you can check for ripple and noise on the power supply outputs? N.B. Check that they are fully isolated from the incoming mains supply first!

The PSU control loop might have gone unstable causing it to oscillate at audio frequencies. This could cause some of the magnetic components to produce audible frequencies through magnetostrictive effects. Even the ceramic capacitors can cause noise through piezoelectric effects.

[edpalmer42]

Take a plastic or rubber tube - size & length don't matter, just make it a convenient length.  Put one end on your ear and move the other end over the board.  You'll easily find the squealer.  Typically, it turns out to be a transformer or inductor.

[rodrigopires]

So assuming its a bad control loop, the source of the problem is that 8 dip chip? Might as well change the eletrolitic caps to BE safe.

[rodrigopires]

Take a plastic or rubber tube - size & length don't matter, just make it a convenient length.  Put one end on your ear and move the other end over the board.  You'll easily find the squealer.  Typically, it turns out to be a transformer or inductor.

I used a plastic stick to poke every component to try to get a feel for the problem, or change in sound, but was unlucky to find the source... That tube/stethoscope looks like a great idea!