Author Topic: Whining capacitors  (Read 1567 times)

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Offline brainwash

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Whining capacitors
« on: December 14, 2016, 07:47:46 am »
This is a dread of mine, I can hear high-pitched electrical noise in a lot of stuff. On one laptop I reflowed some keyboard capacitors to keep a small distance from the pcb, on another laptop I reflowed a display capacitor (0201) to another place and re-arranged the display bezel so it flexes the pcb in another way. PSUs which have whining inductors just get thrown away.

Is there any definitive cure to this? Hot glue or any kind of glue does not work, reflowing to a different position yield limited results. I've also tried all kinds of tapes (scotch, masking, kapton, ...) thinking they might subdue the vibrations but they did nothing.

I would prefer a solution that does not require a soldering iron and a generous bin of capacitors of different dimensions and values. If that is the only way, any recommended brands?
The reason for skipping the soldering iron is that some of those capacitors can be mounted on flex PCBs, with which I'm not rework-comfortable. I have a JBC soldering station and a decent hot-air rework station but still don't feel confident enough to work on very small stuff.

I don't know, maybe epoxy? Or cutting grooves in the PCB? Or just toss it as far as possible and don't keep near the bedroom.
 

Offline Photon939

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Re: Whining capacitors
« Reply #1 on: December 14, 2016, 08:00:18 am »
I had an Nvidia 6600GT graphics card that made annoying PWM noises when running in 3D mode back in the AthlonXP rig years ago. I remember people suggesting dripping superglue into the inductor to reduce the noise.

Epoxy would probably also be a good option.
 

Offline KhronX

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Re: Whining capacitors
« Reply #2 on: December 14, 2016, 08:03:20 am »
Unfortunately, i'm not sure if or how feasible that endeavour is. Ceramic capacitors are, by default, microphonic.

I would imagine, either altering the switching frequency of whatever DC-DC converter they have "upstream" (to shift it away from whatever resonance frequency those caps might have / hit), or figuring out some way to minimise the ripple voltage across the guilty capacitors.
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Offline BBBbbb

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Re: Whining capacitors
« Reply #3 on: December 14, 2016, 08:23:08 am »
I had an Nvidia 6600GT graphics card that made annoying PWM noises when running in 3D mode back in the AthlonXP rig years ago.
Coil whines are quite common in GPUs nowadays.

My Fluke 199c started making noise last week, as soon as I get some time he'll go for a teardown.
« Last Edit: December 14, 2016, 08:25:06 am by BBBbbb »
 

Offline brainwash

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Re: Whining capacitors
« Reply #4 on: December 14, 2016, 11:12:57 pm »
Unfortunately, i'm not sure if or how feasible that endeavour is. Ceramic capacitors are, by default, microphonic.

I would imagine, either altering the switching frequency of whatever DC-DC converter they have "upstream" (to shift it away from whatever resonance frequency those caps might have / hit), or figuring out some way to minimise the ripple voltage across the guilty capacitors.

What do you mean by microphonic? That their audible resonance frequency cannot be altered through mechanical means?
Could perhaps soldering a similar cap on top of a whining one reduce the noise? That's a bit less intrusive than taking the capacitor out, replacing it with another one and praying that it doesn't make the problem even worse.
 

Online wraper

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Re: Whining capacitors
« Reply #5 on: December 15, 2016, 12:08:15 am »
You should replace ceramic capacitors with the same capacitance but with X7R or X5R dielectric type, better with voltage rating as high as possible for particular size. Those whining capacitors most likely have Y5V or Z5U dielectric.
« Last Edit: December 15, 2016, 12:18:58 am by wraper »
 

Online NANDBlog

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Re: Whining capacitors
« Reply #6 on: December 15, 2016, 12:25:04 am »
Age will solve this. I mean, your age, not the electronics age.
I hear also high pitched whining, but now I have a constant few KHz tinnitus, so it is not that annoying anymore. And I also try to keep electronics outside the bedroom.
 

Offline DaJMasta

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Re: Whining capacitors
« Reply #7 on: December 15, 2016, 07:33:48 am »
I think capacitors being microphonic means they will pick up audio noise, not necessarily that will generate it.  If you apply a significant enough AC signal in an audio band, maybe so, but probably not bypass and high speed filter caps, at least.


I wouldn't expect reflowing to help, if it is indeed capacitors, then I would just try replacing them - it's not so much that they're making the noise, but they're degraded performance is making inductors make noise.  It's been suggested on other forums that you can use a tube or roll of paper to try and pinpoint what's actually making noise, and that's probably a good starting point.

If you've got a scope, you could try probing around the noisy parts to see what exactly is going on - maybe that can point you toward what actually needs replacing in the event that it does.  Since the audio band is pretty low in frequency, you probably don't need a really high bandwidth scope - I'd expect a prominent harmonic below 20kHz if you can hear it, and at least that much should show on a scope - maybe sticking to x10 multiplier to be sure you're not interfering as much with the circuit when probing it.  It could be that replacing a filter cap could fix whine in an inductor or something, which at least would reduce the spare parts requirement.


Age will fix it, sure, but it will probably get worse before it gets better - past the teens or so, I think the components prone to making noise may age faster than your own high frequency hearing deteriorates  ;)

Offline brainwash

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Re: Whining capacitors
« Reply #8 on: December 15, 2016, 09:32:02 am »
In my case it was definitely the capacitors doing the noise. Tested with a paper cone as the noise is highly directional and bounces off surfaces. I have a soundfile recorded somewhere, I think it's only 4 or 7Khz. I think anyone can hear it but usually our brain does a lot of noise cancelling. However, once I point it out no one can 'unhear' it. Not being able to filter out noise is definitely a 'software' defect of the brain. Age might help, but, until then, only hardware mods and drinking do the trick.
 

Offline SeanB

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Re: Whining capacitors
« Reply #9 on: December 15, 2016, 03:36:48 pm »
Blob of acetoxy free silicone rubber on each cap will dampen it, and should quiet them a lot. Microphonic caps are able to be a microphone or a speaker, just like crystal earpieces are able to produce sound or generate voltage. Dimension change with applied voltage, or stress causing voltage, the effect is the same of distorting a crystal lattice.
 

Offline CatalinaWOW

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Re: Whining capacitors
« Reply #10 on: December 15, 2016, 04:14:24 pm »
There are several fundamental ways to stop a noise like this.  There are no magic bullets in the sense of being, easy, cheap and effective.

First way is to eliminate the source.  If the whine is a piezo effect in the capacitors you have to change the capacitor type as others have already suggested.  It is also possible that defects in physical construction could be allowing pure electrostatic attraction to be the transducer-again change the capacitors.  Finally you can try to eliminate the ac component of the voltage on the capacitors which is driving the transduction mechanism.  This is basically impossible in existing designs, and would drive things like selecting a linear architecture for supplies if you have control of the design.  So not a very attractive solution.

The second way is to add damping to reduce the magnitude of the motion.  Putting some lossy material where the whining component has to move it and allowing it to suck up the energy.  The problem is that most glues and RTVs are not very lossy.  Something like wet mud might work, but keeping it wet and where it belongs is a real problem.  There are some audio materials that claim to be lossy.  Some actually are, but nothing magic.

A third way is to shift the resonant frequency of the whining capacitor away from the driving frequency.  This doesn't eliminate the noise, but can reduce the amplitude a lot.  Changing stiffness is one way, and this is what glue attempts to do, but it often isn't stiff enough to really help.  A rigid glue like epoxies or cyanoacrylate is the right direction, but may cause other problems due to CTE mismatches as temperature changes.    Changing mass is the other way, and can be more effective.  Lead foil or solder glued on with a rigid glue.

A fourth way is insulation.  The component still whines, but the sound is confined and you don't hear it.  Sound absorbing materials aren't that hard to find, but it is hard to find all of the paths by which the sound escapes and also hard to block some of them once identified.  The best way to implement this method is to turn the equipment on and then leave the room.  There are actually a lot of situations where this can work.
 


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