Author Topic: How to fix switching noise (acoustic noise) from power supplies?  (Read 289 times)

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Offline Odd

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I just received two ViewSonic displays I bought, and while they otherwise perform as expected, there is a rattling noise from some inductors, I can imagine, inside.
In a very quiet environment, like my office, this drives me crazy, I could easily return them, but it would be cool to fix.

Frequency may be below 5khz, in terms of db it is not very loud.

So, how does one proceed on quieting a noisy switch-mode PSU?   - Does it work to locate the correct coil(s) and ...epoxy them?

 

Offline T3sl4co1l

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Re: How to fix switching noise (acoustic noise) from power supplies?
« Reply #1 on: February 17, 2020, 09:38:03 pm »
Standby or active?

If standby, it's probably pulsing infrequently to maintain voltage.  The pitch can vary with mains supply voltage and will vary with load.  Not much you can do here: the noise is likely due to magnetostriction in the core.  That is, the core itself is straining due to applied magnetic field.  The core is quite stiff, so it's not like you can keep it from straining by putting rubbery goop on it.  About all you can do is add padding to absorb the sound (which may however still involve rubbery goop, say to dampen the PCB).  Be careful with padding, so as not to block airways.

If active, it may still be the above, if not on the main supply(ies) then on an aux supply or something perhaps.  Otherwise, it may be poor compensation, which may suggest aging electrolytics, or poor component choice in the first place.

Heh, also, if it has powered speakers internal or attached, those could be squealing, for similar or different reasons.

Tim
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Offline David Hess

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Re: How to fix switching noise (acoustic noise) from power supplies?
« Reply #2 on: February 18, 2020, 05:33:58 am »
Otherwise, it may be poor compensation, which may suggest aging electrolytics, or poor component choice in the first place.

Just to elaborate on this, high ESR from worn out capacitors can cause false triggering and noisy operation of the switching controller resulting in audible subharmonic oscillation.  This is good because many of there other causes would require redesign.
 

Offline Odd

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Re: How to fix switching noise (acoustic noise) from power supplies?
« Reply #3 on: February 18, 2020, 08:58:59 am »
the noise is when active.
The pitch changes with overall brightness, I suspect it is not the main PSU, but CFL supply.
I plan to return the displays and get some other brand/series.
 


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