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Old 03-09-2022, 09:38 AM   #1
jayjr1105
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Default Laptop power brick audibly noisy

I wired this up with a apple airport cable so it would fit my Pinecil soldering iron and not have a stupid heavy ferrite bead at the end near the plug. The noise changes depending on the load. With a 9w load it's less frequent and with a laptop 50w+ load it's higher pitched. If I press on the transformer with something plastic it also gets a little quieter. Any danger here? Am I actually hearing the switching of the FET? It's like tapping not really squealing like coil whine.

I realize it's probably a low end little brick but it came apart super easy without any cracking or melting of the case so I decided to use it. I probably have a dozen other 19v 3a bricks I could use instead if this is a hazard.
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Old 03-09-2022, 03:40 PM   #2
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Default Re: Laptop power brick audibly noisy

well squeeling is often bad caps early on.
in this case i would get shot of that bs mylar snubber cap and fit a 2KV ceramic - while it's out you can check the associated resistor
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Old 03-10-2022, 11:29 AM   #3
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Default Re: Laptop power brick audibly noisy

Definitely not cap squealing. It's coming from the transformer it would seem. It's like a soft rapid tapping.
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Old 03-11-2022, 03:14 AM   #4
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Default Re: Laptop power brick audibly noisy

Quote:
Originally Posted by jayjr1105 View Post
Definitely not cap squealing. It's coming from the transformer it would seem. It's like a soft rapid tapping.
I think that's normal?
Reason I say that is because my Aoyue 2900 soldering station does the same thing - sounds like light tapping/clicking, and it is synchronized with the PWM pulsing of the station's tip-diving MOSFET. And likewise, the sound is coming from the transformer on the station... though in my case, it's worth noting that the 2900 / CS2900 uses a classic line-frequency transformer rather than an SMPS.
In any case, though, I've had that station since ~2012. So if it hasn't failed after 10 years, I suppose it's OK.

Quote:
Originally Posted by jayjr1105 View Post
I realize it's probably a low end little brick but it came apart super easy without any cracking or melting of the case so I decided to use it. I probably have a dozen other 19v 3a bricks I could use instead if this is a hazard.
It looks OK.
Transformer looks big enough and also probably has OK primary-secondary insulation.
Seems like you've already recapped it with good caps (minus the mains, but that's probably OK for a good while usually.) Therefore, I don't expect you'll see any major failures, if at all.
As long as the adapter uses some kind of current-mode PWM controller to drive that MOSFET on the primary, it should be decently safe enough to use. But if it's a 2-transistor self-oscillating design, I'd definitely not advise to leave it plugged in unattended.
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Old 03-11-2022, 09:44 AM   #5
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Default Re: Laptop power brick audibly noisy

Quote:
Originally Posted by momaka View Post
I think that's normal?
Reason I say that is because my Aoyue 2900 soldering station does the same thing - sounds like light tapping/clicking, and it is synchronized with the PWM pulsing of the station's tip-diving MOSFET. And likewise, the sound is coming from the transformer on the station... though in my case, it's worth noting that the 2900 / CS2900 uses a classic line-frequency transformer rather than an SMPS.
In any case, though, I've had that station since ~2012. So if it hasn't failed after 10 years, I suppose it's OK.


It looks OK.
Transformer looks big enough and also probably has OK primary-secondary insulation.
Seems like you've already recapped it with good caps (minus the mains, but that's probably OK for a good while usually.) Therefore, I don't expect you'll see any major failures, if at all.
As long as the adapter uses some kind of current-mode PWM controller to drive that MOSFET on the primary, it should be decently safe enough to use. But if it's a 2-transistor self-oscillating design, I'd definitely not advise to leave it plugged in unattended.
It seems to have quieted down a little but still that light tapping. I've actually used it for the past couple days to power an old 2010 laptop which I use for my USB microscope and no issues. It gets warm but that's with a 40-50w load. How can I tell if it's a 2 transistor self-oscillating design?
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Old 03-11-2022, 12:18 PM   #6
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Default Re: Laptop power brick audibly noisy

Quote:
Originally Posted by jayjr1105 View Post
... How can I tell if it's a 2 transistor self-oscillating design?
A quick clue would be if there is no PWM IC and if there is no all-in-one TO-220 switching regulator IC (e.g. Power Integrations' TinySwitch or TopSwitch ICs).

Backing up a bit, your picture in the OP shows the adapter is a flyback design (no output inductor). On the secondary side you'll probably find a TL430 or TL431, which is connected to an optocoupler. The optocoupler could provide a feedback signal to a PWM or all-in-one, or it could drive the turn-off transistor in a two-transistor design.

In a flyback topology, the "output transformer" is actually a coupled inductor. The primary winding serves as the inductor, and the stored energy from each "on" cycle is coupled into the secondary circuit.
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Old 03-11-2022, 12:19 PM   #7
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Default Re: Laptop power brick audibly noisy

Quote:
Originally Posted by jayjr1105 View Post
How can I tell if it's a 2 transistor self-oscillating design?
Just see if there is an SMPS IC on the bottom of the PCB (specifically on the primary side.)
*EDIT*
I guess PeteS beat me to it.

Last edited by momaka; 03-11-2022 at 12:22 PM..
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Old 03-11-2022, 09:59 PM   #8
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Default Re: Laptop power brick audibly noisy

It's one of the cheaper "laptop replacement" power supplies.
Almost the same board as one I scrounged for parts, bigger transformer, same heatsinks- just wider, and the same lack of input filtering/inrush limiting.

The small cap for the PWM IC is suspect, no matter what the markings are (can be fake).
Use a 22-47u 50v 105 degree, such as PW, HE, FC, FR. For the output caps, use the largest value at 25v that physically fit.
I like FR here, large capacitance for their size & low ESR/hi ripple to handle that flyback supply.
Looks like the caps are 680u/25v.
Try for 1000-1500u/25v, again the largest value that fits.
Also tie the EGC from the AC inlet to the DC side negative.
Looks like you've got a 3-wire AC inlet with the GND unconnected!


IIRC, the control IC works like a 384x. It's a 6 or 8 pin SMD part on the back of the PCB.
I'm pretty sure the 8-pin version does not share the 384x pinout!

I find the output rectifier to be a weak link in these- change it to a 100v/20A schottkey or SBR part.
UFs or FRs have higher Vf and the heatsink gets hotter.

This is a drop in, complete with isolated tab:
https://www.mouser.com/ProductDetail...OZiNSM5g%3D%3D
Get one while you can...

re: the noise. It's likely you're hearing the PWM modulate as the iron pulses the element.
But change the caps anyway; again, they're known to be questionable in these "replacement power" adapters.
Is that small cap original? "Looks like" a Panasonic FC- did you change it already?
The transformer should be OK. I see what appears to be nice layering & teflon tubing on the lead wires.
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Last edited by kaboom; 03-11-2022 at 10:09 PM..
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Old 03-12-2022, 01:06 PM   #9
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Default Re: Laptop power brick audibly noisy

Okay, front TO-220 shaped device is "First" 16T41 - FIR8N60F and Secondary side is also "First" branded 16M01 - MBRF20100
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