Re: Can an electrolytic capacitor "sing"?

From: Robert Monsen (rcsurname_at_comcast.net)
Date: 03/28/05 

Date: Mon, 28 Mar 2005 01:13:38 -0800

ohaya wrote:
>
> Dave VanHorn wrote:
>
>>Parallel plates, very close together, with varying applied field, will have
>>a varying attractive force between them. I've heard this at 120 Hz in bridge
>>rectifier systems where the cap was overlarge and the diode conduction angle
>>was rather narrow.
>
>
>
> Hi,
>
> I've got the motherboard completely out of the case now, with the power
> supply outside also, and separated with some material to deaden the
> sound from the power supply.
>
> After running the motherboard for awhile, I think that I've gotten it to
> emanate the sound. It's much lower in volume, probably since it's
> outside of the case now.
>
> What I've been doing is to block off area by area with a thick pad of
> newspaper, to try to isolate where the sound is coming from, and, I know
> that this is going to sound very weird, but it sounds like it's coming
> from the CPU itself, or something within the footprint of the CPU.
>
> If I place my 'sound barrier on one side of the CPU, immediately
> adjacent to the CPU/heatsink, I can hear the sound (it's actually more
> like a 'squealing' sound) from the other side of the CPU. In this case,
> the sound is probably coming through the channels between the heatsink
> fins.
>
> If I place my sound barrier on the direct opposite side of the
> CPU/heatsink, I can't hear the sound.
>

I wonder if convection is causing air to whistle thorough the heatsink?

I recently debugged my own mainboard noise issue. It turned out that the
CPU heatsink was clogged with lint, and was causing the fan mounted on
the heatsink to spin twice as fast as it should have been doing. Also,
there was a bit of high frequency noise that could have been interpreted
as whistling. Cleaning out the lint quieted the system down quite a bit.

> On the motherboard, around the CPU socket (actually kind of underneath
> the edge of the CPU socket, I can see a couple of surface mount ICs and
> surface mount resistors or caps, but that's all that's there. I've
> tried tapping some of those to see if it affects the sound, but no
> change.
>
> So now, I guess I have to change my question: Is it possible for a CPU
> chip to "sing" or make this "squealing" sound??
>
> Again, I know that this sounds a bit strange, so my apologies.
>
> Jim 

-- 
Regards,
   Robert Monsen
"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

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