Construction and power supply of the 3kW Fibaro Switch module - photos and descriptions

kemot55 wrote:

The only thing that can be complained about is the width (cross-section) of the strong-current paths (in my opinion).

Not necessarily. Copper can, after all, be 70 or even 150um thick.

Or rather a Viper circuit. Such a Buck inverter operating with an input voltage of 230V, giving a few V at the output.
Because I don't see a tray there, just a coil (and that rules out a Flyback converter).

An unloaded inverter squeaks. E.g. in the transformer, the core has cracked or it is simply not sealed well with varnish.

It was already very simple. And unfortunately there is usually nothing you can do about the squeaking.
If you didn't even understand my description then all the more reason not to do anything here.
If you were sure that it is not a cracked core but just a flying whole core, then you could try pouring paraffin over it. But that might be a problem, as paraffin is hard to come by these days. That stuff from the candle refills is not paraffin (I recently had a chance to find out). If not paraffin, then with an electro-insulating varnish (you can also use Uretolux).
It's just that it will all come to a comparable cost to postage.

The squeaking itself is not dangerous. What may be dangerous is what leads to the squeaking.
You can apply paint, but even the cheapest paint costs about 20PLN, which I understand is too expensive for you (that's how much it would cost to send it for repair, which I understand is too expensive for you).
Replacement is not possible. The transformers in the inverters are custom-made for almost every inverter.

Oh, I forgot that there is an uninsulated inverter on the coil and not the transformer.
Well it might be a bit easier to replace it.
The danger could be a cracked core. Because if it's cracked, a piece can fall out of it at any time. This will change the parameters of the coil and the whole power supply can burn out.
I will not mark this coil for you. You have to locate it yourself. Let's say it's a test for your ability to repair it

This is the component. First check that it is definitely the one that squeaks.
Nail polish could be if we checked its composition.
But that nobody gives its composition is a bit of a risk.
It certainly can't be gold, silver or grey nail varnish, because this can contain silver or graphite particles and can therefore be a bit conductive.
Clear is the safest.
But as I say, there is no certainty here.
The only varnish that is not a dedicated electro-insulating varnish, but is proven and reliable, is Uretolux (and by the way, it is very cheap, about 20zl for 1l).
Oh, and one more thing. Varnishing a coil in which the core has cracked will only make matters worse (the varnish may widen the gap and thus burn out the inverter).
So a cheap repair may be possible here, but first you need to make an accurate diagnosis. And this remotely will not be done. And you don't have a clue about it at all. Well, that's what the whole situation looks like.

Well, it's hard. If it's live, I wouldn't recommend putting your ear to it.
First check (without voltage) whether the core in this coil is cracked.

Well, it won't do. The only advice I can give you is to have it repaired by someone else.
Not even because it's a waste of your life.
It's just a waste of time explaining it.