Can an electrolytic capacitor "sing"?

O

ohaya

Guest
Hi,

I've been going crazy trying to track down a high-pitched "whistling"
sound coming from a new computer system that I've been building. After
a lot of testing, it looks like the whistling sound is coming from the
motherboard itself.

In particular, the area of the motherboard looks like it contains some
power-type circuitry, with 3 large electrolytic capacitors, and two
toroidal coils "standing up". Once the sound is there (it seems to
start after the system has been on for awhile), I've tapped, poked, and
jiggled the various components, but none of this seems to alter the
sound.

Since I've tapped the toroids while the sound is there, and it doesn't
change the sound, I'm wondering if it's possible that this whistling
sound could be coming from one of the capacitors themselves?


The caps and the toroids are right adjacent to the CPU, and with the CPU
fan blowing into heatsink, I've noted that the caps get very hot. As a
test, I've reversed the direction of the fan, so that it's removing hot
air from the heatsink, and when I did this, the caps are much cooler,
and so far, I don't get the whistling sound.

Hopefully, this will have eliminated the whistling sound, but I'm a
little worried that I haven't been able to isolate exactly where the
sound is coming from, and I'm still very curious about what might be
causing it.

Any thoughts or insights that you all here might have on this would be
greatly appreciated.

Thanks in advance,
Jim
 
On Sat, 26 Mar 2005 23:32:03 -0500, ohaya <ohaya@cox.net> wrote:
Hi,

I've been going crazy trying to track down a high-pitched "whistling"
sound coming from a new computer system that I've been building. After
a lot of testing, it looks like the whistling sound is coming from the
motherboard itself.
....
Click to expand...

The caps and the toroids are right adjacent to the CPU, and with the CPU
fan blowing into heatsink, I've noted that the caps get very hot. As a
test, I've reversed the direction of the fan, so that it's removing hot
air from the heatsink, and when I did this, the caps are much cooler,
and so far, I don't get the whistling sound.
Click to expand...
There were a gadzillion motherboards manufactured with defective caps around
'99-'01. Basically a Taiwanese company put out caps specd for 6V that were
probably 3V caps. Look for bulging caps. If they're running hot, then they're
defective.

You either have such defective caps, or perhaps a bad power supply; make sure
it's voltages are correct.
 
TCS wrote:
On Sat, 26 Mar 2005 23:32:03 -0500, ohaya <ohaya@cox.net> wrote:
Hi,

I've been going crazy trying to track down a high-pitched "whistling"
sound coming from a new computer system that I've been building. After
a lot of testing, it looks like the whistling sound is coming from the
motherboard itself.
...

The caps and the toroids are right adjacent to the CPU, and with the CPU
fan blowing into heatsink, I've noted that the caps get very hot. As a
test, I've reversed the direction of the fan, so that it's removing hot
air from the heatsink, and when I did this, the caps are much cooler,
and so far, I don't get the whistling sound.

There were a gadzillion motherboards manufactured with defective caps around
'99-'01. Basically a Taiwanese company put out caps specd for 6V that were
probably 3V caps. Look for bulging caps. If they're running hot, then they're
defective.

You either have such defective caps, or perhaps a bad power supply; make sure
it's voltages are correct.
Click to expand...

TCS,

This motherboard is fairly new (purchased a couple of weeks ago), and
the model is, as I understand it, also fairly new (Abit VA-20), so I
would hope that they're past the capacitor problem by now.

I think that the caps were only hot because of the CPU fan blowing into
the heatsink, and the motherboard design was such that the channels in
the heatsink basically routed all of that hot air directly towards the
areas where the caps and the toroid are. Once I reversed the fan
direction to suck hot air from the heatsink, the caps were almost cool
to the touch.

What I'm trying to figure out is: If these caps and/or the toroid got
heated up, is there any possibility that the caps would emanate this
whistling sound on their own (i.e., not due to caps touching each
other)?

I'm running a long-running load test on the system now, and with the fan
sucking hot air from the heatsink, the whistling hasn't occurred, so I
think that I'm close to proving that something is "singing", probably
due to the heat. I'm just not sure what it could be.

Thanks,
Jim
 
"ohaya" <ohaya@cox.net> wrote in message news:42463743.8EA50986@cox.net...
Hi,

The caps and the toroids are right adjacent to the CPU, and with the CPU
fan blowing into heatsink, I've noted that the caps get very hot. As a
test, I've reversed the direction of the fan, so that it's removing hot
air from the heatsink, and when I did this, the caps are much cooler,
and so far, I don't get the whistling sound.

Hopefully, this will have eliminated the whistling sound, but I'm a
little worried that I haven't been able to isolate exactly where the
sound is coming from, and I'm still very curious about what might be
causing it.

Any thoughts or insights that you all here might have on this would be
greatly appreciated.
Click to expand...

Electrolytic capacitors don't usually make human audible noise (or if so of
only minor volume). Z5U and other high K dielectric ceramic capacitors on
the other hand can make lots of audible noise. However, I would be much
more suspect of those toroids making the noise. All magnetic components can
make lots and lots of human audible noise if the current flowing through
them changes with frequency components less than 20kHz. The CPU core
powersupply might be on the verge of unstable (perhaps improper loop
compensation, either by design or because there is a specific problem on
this motherboard). As the components heat up small parametric shifts of
component characteristics might cause the powersupply to become somewhat
unstable. As a consequence the current through the inductors in unstable
and they make lots of noise.

If this is the case I would be tempted to return the motherboard if you
still can.
 
Fritz Schlunder wrote:
"ohaya" <ohaya@cox.net> wrote in message news:42463743.8EA50986@cox.net...
Hi,

The caps and the toroids are right adjacent to the CPU, and with the CPU
fan blowing into heatsink, I've noted that the caps get very hot. As a
test, I've reversed the direction of the fan, so that it's removing hot
air from the heatsink, and when I did this, the caps are much cooler,
and so far, I don't get the whistling sound.

Hopefully, this will have eliminated the whistling sound, but I'm a
little worried that I haven't been able to isolate exactly where the
sound is coming from, and I'm still very curious about what might be
causing it.

Any thoughts or insights that you all here might have on this would be
greatly appreciated.

Electrolytic capacitors don't usually make human audible noise (or if so of
only minor volume). Z5U and other high K dielectric ceramic capacitors on
the other hand can make lots of audible noise. However, I would be much
more suspect of those toroids making the noise. All magnetic components can
make lots and lots of human audible noise if the current flowing through
them changes with frequency components less than 20kHz. The CPU core
powersupply might be on the verge of unstable (perhaps improper loop
compensation, either by design or because there is a specific problem on
this motherboard). As the components heat up small parametric shifts of
component characteristics might cause the powersupply to become somewhat
unstable. As a consequence the current through the inductors in unstable
and they make lots of noise.

If this is the case I would be tempted to return the motherboard if you
still can.
Click to expand...
Hi,

I ran a "load test" for 2 hours, with the fan reversed, and no sound,
but after leaving the system on for most of the night, it came back. At
this point, I think that you may be right.

Sigh...

Thanks,
Jim
 
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.
 
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.

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
Click to expand...

P.S. In case anyone is interested, I've uploaded a WAV file of a tape
recording that I made of the sound when the board was in the case. As I
mentioned above, the sound was much louder when the board was in the
case. I did the recording with one of those voice recorders.

The WAV is at: http://members.cox.net/ohaya/AbitNoise.wav

Thanks again,
Jim
 
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.
Click to expand...
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
Click to expand...

--
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.
 
Neo wrote:
Hey, just one other doubt, why dont you check if the fan bearings have
got busted by chance.
Click to expand...

Hi Neo and Robert,

As I think that I mentioned, the CPU fan was not powered on when I did
this "listening" test, so the noise is not coming from the CPU fan.

Jim
 
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.
Click to expand...

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.

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
 
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