Can an electrolytic capacitor "sing"?

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

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

got

yep, seen it happen. Normally because overvoltage applied, or caps faulty. They do tend to explode sooner or later - usually sooner.

fan

If it dies it'll be easier to fault find, and its under gtee anyway. Get over it basically.

NT

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.

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.

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

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:

Thanks again, Jim

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.

Hey, just one other doubt, why dont you check if the fan bearings have got busted by chance.

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

CPU

ICs and electrolytic caps can both sing when in their death throes. How long they can go on like that before cracking up I dont know.

Suggest you find some interests in life.

NT

Have you tried the "stiff rod" trick yet?

Get a length of rigid material, maybe a pencil or piece of plastic tubing, and press one end against a component to test, and your ear to the other end. Great for diagnosing hard-to-find problems (I like to use it to find which valves need adjusting when working on motorcycles.) :)