Test OK (no, it isn't) PSU

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cobrano

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Apr 13, 2017
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1 month ago i purchased a new psu, a Corsair CX450M. One day, i heard that i makes the exact noise like in this video: https://youtu.be/iZKI1hcTPyg
It happens when it is connected to the connector, and the PSU is switched on. (The computer isn't)
I wrote to my reseller, they said it is supposed to be a faulty psu, i sould bring it back to them. So a brought it back. After 2 weeks (today) i got an email, which said test OK. I couldn't even imagine how that can be possible. My question: Should i rma it to Corsair? Great, i have to pay for the shipping, but here in hungary people have to do everything on their own
 
Solution
InvalidError
If whoever said the PSU was 'ok' correctly tested the PSU, then ripples on 5VSB should be well within tolerances and shouldn't be a problem.

BTW, when the computer is in soft-off state with nothing drawing power from 5VSB, the pulse-skipping / non-continuous mode will cause looser output regulation. That isn't really an issue at that point since the 5VSB is only powering the soft-on button and RTC. And yes, those modes are normal since the switching controller has a minimum duty cycle and when even the minimum duty cycle isn't low enough to prevent the output voltage from creeping up, it has to skip pulses to bring it back down.
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InvalidError

InvalidError

Titan
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May 18, 2007
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That would be the sound of the 5VSB supply operating in some form of pulse-skipping mode. Some amount of noise is to be expected from the circuit periodically turning on and off, but it should be barely audible. If you can still clearly hear it when the PSU is installed in a closed case and connected to the motherboard, then that should qualify as excessively loud.

Some of my PSUs make similar noises but I need to have my ear very close to the PSU to hear it.
 
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C

cobrano

Commendable
Apr 13, 2017
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Sorry, i forgot to say, this isn't my psu, i just find a very similar video to my "problem"
Can this be normal? Maybe they couldn't hear the noise?
I couldn't belive it, i was about to explode...
Yeah, this is some kind of electrical noise
 
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InvalidError

InvalidError

Titan
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May 18, 2007
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That the video wasn't from your own PSU was kind of implied by the "like this video" and doesn't change the fact that this is a typical pulse-skipping PSU noise or that this type of noise shouldn't be particularly loud.

Pulse-skipping is something that some PSUs do when under very light load to improve efficiency. It should go away when you increase the load on the 5VSB output enough to get out of the pulse-skipping low-power mode. If your motherboard isn't drawing enough power from 5VSB to get there, try charging your phone/tablet from one of the motherboard's always-on USB ports if it has any.
 
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jonnyguru

jonnyguru

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Nov 30, 2006
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List your system specs.

Does the PSU make this sound ALL OF THE TIME or only under certain conditions?

If only under certain conditions, what are those conditions?

The reseller could have "tested good" because their conditions could be different from yours.
 
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InvalidError

InvalidError

Titan
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May 18, 2007
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The name of the game here is to increase the load on the 5VSB rail while the PC is off to see if that will make the 5VSB supply go from pulse-skipping mode to continuous. The easiest way to achieve that would be to charge your phone or other mobile device on an always-on/charging port from the motherboard as that will draw 400+mA and should be more than enough to get the 5VSB supply into its steady mode. The monitor, network and other stuff don't draw power from 5VSB, so they don't help with that. (The network would add a little bit, if you enable wake-on-LAN.)

Another thing you could try is putting your PC into sleep mode (not hibernate) as that would load down the 5VSB output with 1-2W to keep the RAM in self-refresh state.
 
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C

cobrano

Commendable
Apr 13, 2017
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InvalidError: Thank you, i will try that

UPDATE: I installed another psu, an fsp hexa+ 400w just to see if it makes noise, it's dead silent, but i didn't connect my samsung dvd drive to it - can it be the root of the problem?
 
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C

cobrano

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Apr 13, 2017
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Okay, i will do everything today, but it won't damage my system, right? Sorry for the lot of questions. I also read on Corsair forum, the noise i can hear a foot away is normal, but then why the other psu didn't do it :/
 
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InvalidError

InvalidError

Titan
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May 18, 2007
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When I had an issue with the 5VSB supply causing noise over my amplifier when the computer was off, I "fixed" it by wedging a 47 ohms resistor in the back of the 5VSB line (purple wire) and ground on the ATX power connector. Not ideal for power efficiency, but that got me a few more years of quiet operation before it quit working properly and I replaced it.
 
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InvalidError

InvalidError

Titan
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May 18, 2007
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As I wrote earlier, some amount of noise at very light 5VSB load is to be expected due to the supply operating in discontinuous mode, some are noisier than others depending on design and component selection.

How harmful or not it might be, you'd have to check how much ripple is on the 5VSB line with an oscilloscope to determine that.
 
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C

cobrano

Commendable
Apr 13, 2017
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Sorry for the lot of questions, so this discontinous mode is normal at power supplies, at some i can hear, at some i can't? Right now i can't get an oscilloscope but i'll look for one
 
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