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Any opinions on the AiXun T3A?

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drksy:
So after some more experiments tonight, I finally managed to eliminate the buzzing. Here's the circuit I built, essentially moving the high power path out of the circuit, and also providing a separate, isolated supply to run the high current loop.



I didn't have any high power PMOS at hand, so I used one of my spare IRF3710 n-channel MOSFETs as a high-side switch by adding an extra, isolated 8V supply to drive the gate. A boost converter could also be used here.



Running this, it was absolutely silent. I didn't hear any buzzing whatsoever from the board or the any of the supplies.

Next, I removed the 24V bench supply and used Aixun's own 24V supply:



And what do you know, everything started buzzing again! What's going on here!! It seems when the high power path shares the same supply as the analog control circuit, the thing just starts buzzing.

It was already getting late, so I ended it here. My next try is going to be supplying the 2.8V for the digital section straight from an isolated bench supply and see if that does anything.

dreamcat4:
And here i was just assuming that it depended on the grounding... (for example if you touch the tip to a grounded objects whilst soldering, or if the aixun base station is plugged into a poor grounding, or if the 1mohm static grounding resistor explodes due to static shocks, things like this).

T3sl4co1l:
Aha, so it's not the element buzzing, it's the supply.

On the upside, the proposed solution still works, if just moved over to the input to the switch (i.e. an LC filter between supply and switch); of course, it's no more economical there, either. ;)

That suggests the noise is probably core magnetostriction from the supply throttling up and down regularly (and suddenly); it might even be going idle inbetween pulses.  Replacing the supply with a quieter one is the most expedient route.  Digging into the SMPS yourself would be... more challenging.

I suppose I'm still only assuming it's SMPS, as I haven't seen complete up-close internal photos of this thing.

Tim

dreamcat4:
i think you have to ultimately realize that at least 1 component somewhere in the box is making a sound. and whether thats from a magnetic coil, or its a microphonic peizo from an mlcc or something else. then that component either isn't locked down properly enough, or it's basically gone faulty / bad and may be a subject for possible replacement. since it's making a noise after all...

but the reason that it is resonating is because there is a resonance occuring at some specific frequency, due to a resonance occurring or being driven in the circuit.

so if you think about somethingg like a power brick (or smps) if it's not grounded but isolated / floating. then this is why i am saying maybe there is some grounding issues. whereby that floating is not tied to anything, thus permitting such a resonance to occur between multiple parts of the circuit. to generate that.

but what do i know eh? but what i am really saying is look at your active circuitry and whether powered internal or external. and whether the tip is getting grounded or is left floating when touching the target metal object (the thing that you are actively soldering). that is when the output is being driven to pwm and put the heat / power into the tip.

and then maybe something can fall out here and makes a better sense from it. to inform what you might try to measure next. or identify how to disable buzzing more reliably. and under which specific conditions.

unfortunately i cannot help you here on my unit because... it never buzzes. it's totally fine under all of the circumstances (because 0 components is faulty, nothing is due for replacement for this matters). however if the station did buzzes, i just simply would not care to matter enough. because it's too minor matters to really bother fixing it. i would probably just choose to live with the buzzing issue. (but so long as it was not too high pitched or nasty sounds, there is different types of buzz).

T3sl4co1l:
The fact that no one else has reported noise, does sound suspicious.

Maybe they changed the design, maybe you got a counterfeit, but maybe more likely it's just a magnetic core or capacitor or something has come loose.

Note that capacitors and magnetic cores (by piezoelectricity for ceramic caps, and electro/magnetostriction otherwise) make noise even when fully anchored; these effects result in strain of the bulk material itself.  It's usually a small effect, and in particular I would expect voltage changes to be small (at least, if the supply is operating nominally, i.e. compensation is adequate) so that capacitors can be ruled out, and that leaves cores, hence my proceeding reply.  But again, this would apply to any unit, and a loose core able to rattle, or move due to attractive forces, or wires in the windings by repulsive forces, would be a viable explanation for additional noise.

Not necessarily "faulty" components, but, different in some way, seems likely.

Tim

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