YouTube video with the sound

What is this sound, and why does it happen? After discharging the motherboard (turning it on without a power source), and then powering it with a battery, it makes that high pitched noise (before the buzzer beep). Is it the capacitors charging? It makes the same sound every time I do this.

 

YouTube video with the sound

What is this sound, and why does it happen? After discharging the motherboard (turning it on without a power source), and then powering it with a battery, it makes that high pitched noise (before the buzzer beep). Is it the capacitors charging? It makes the same sound every time I do this.

Welcome to AAC.

I can't hear the sound you are talking about in the video but it seems most likely it is a boost or buck converter starting up. Boost and buck converters, as well as SMPS (Switch Mode Power Supplies) use high frequency oscillators to do their work. It is possible that the circuit is ramping up to what will definitely be an inaudible frequency (well outside human hearing).

It is usually an inductor that makes the noise. Sometimes it will make an audible sound even while running at the intended frequency due to a harmonic that does lie in the audible range. In any case, do you suspect something is wrong with the board?

 

I can't hear the sound either, but here's its spectrum, courtesy of Audacity :-

 

I hear a click just before the bee-bee-beep. Is that what you mean?

 

I hear a click just before the bee-bee-beep. Is that what you mean?

Yes, with a high pitch thereafter that goes to a lower pitched sound.

 

Welcome to AAC.

I can't hear the sound you are talking about in the video but it seems most likely it is a boost or buck converter starting up. Boost and buck converters, as well as SMPS (Switch Mode Power Supplies) use high frequency oscillators to do their work. It is possible that the circuit is ramping up to what will definitely be an inaudible frequency (well outside human hearing).

It is usually an inductor that makes the noise. Sometimes it will make an audible sound even while running at the intended frequency due to a harmonic that does lie in the audible range. In any case, do you suspect something is wrong with the board?

Thank you very much for this detailed answer! I really appreciate it.

I did not really suspect that something is wrong, more that I take precautions because of the weird sound. But could something happen if I plug in the battery for a longer amount of time?

 

I can't hear the sound either, but here's its spectrum, courtesy of Audacity :-
View attachment 302614

Interesting! About 150 Hz - does that give any clues to what it is?

 

Thank you very much for this detailed answer! I really appreciate it.

I did not really suspect that something is wrong, more that I take precautions because of the weird sound. But could something happen if I plug in the battery for a longer amount of time?

There is no reason to think that the sound has anything to do with a malfunction. If something happens, it won't be because of that.

 

About 150 Hz - does that give any clues to what it is?

Third harmonic of mains frequency, if your mains is 50Hz.