Extremely high-pitched squealing noise when computer is off

MaximRecoil

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Aug 30, 2005
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I'm thinking this might be the power supply. Are there any other components in a PC that electricity is running through when the power is off that could be making the noise? I know that electricity runs through the motherboard when the PC is turned off, at least to the point of the motherboard's LED, but I don't know if there are any components in that path on the motherboard which could be making the noise.

When the computer is unplugged or turned off via the power supply's rocker switch, the noise continues for a couple/few seconds and then you can hear it quickly wind down and stop.
 

Lmeow

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Try locating the noise. I would think it's the power supply - if you want to try removing the 24 pin ATX motherboard plug when the PSU is off, and turn it back on (while the computer is off) and see if there is any noise. If there is any noise... then you definitely know it's the PSU. The reason why I think that it's the PSU is because if you turn it off directly through the PSU switch, if it was the motherboard then the sound would die instantly or at least close to a second, not two or three as no more current would run through it. That's what I think.
 

Lmeow

Splendid
Try locating the noise. I would think it's the power supply - if you want to try removing the 24 pin ATX motherboard plug when the PSU is off, and turn it back on (while the computer is off) and see if there is any noise. If there is any noise... then you definitely know it's the PSU. The reason why I think that it's the PSU is because if you turn it off directly through the PSU switch, if it was the motherboard then the sound would die instantly or at least close to a second, not two or three as no more current would run through it. That's what I think.
 

MaximRecoil

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That's a good idea. I removed the 24-pin connector from the motherboard, and then flipped the power supply's rocker switch on; and it made the squealing sound. So yeah, it is definitely the power supply.

That's too bad; it has been a good power supply (an 500W Antec that I bought new 4 years ago). I assume it is a capacitor or capacitors in there making the noise, which would be an easy and cheap fix, but I don't think the PSU's housing is designed to open up (though I haven't really taken a look at it).

I recapped a 25-year-old Nintendo video arcade machine switching power supply (model PP1000A) several months ago; replaced all of the electrolytic capacitors (13 of them); and the total cost was about $10. There was nothing wrong with the power supply, I did it just as a preventative measure given its advanced age. Interestingly, one of the 3300UF 10V filter capacitors in there wasn't soldered at all on one leg, and it never had been (it had been missed during manufacture), but it never seemed to affect its function.
 

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