hx 850 12v rail dropping to 11.75?

Is this acceptable? or not? I do not have any idea where any of my purchasing paperwork is for the PSU, so an RMA may be difficult if not impossible :(. It will read 12.09 on the 12v rail in windows, but put a graphics load on it (BF3) for example, and it will drop down as low as 11.75, causing instability. This seems to have begun quite recently, as I do not recall having this problem before this last week or so.

Thanks!

Michael.

P.S., any ideas? I can disassemble / reassemble case / PSU cables and such if people think it will help at all, but that hasn't changed...

The ATX PSU spec is +/- 5%, i.e. 11.40V-12.60V, so 11.75V is within spec. and only a ~2% drop under load - if the voltages shown are correct.

The only means however to tell if the voltages shown by the software are accurate - and often they are not, is to measure the voltage with a digital volt meter. 11.75 V should not cause stability issues as this voltage is dropped down at the mobo/GPU. The mobo/GPU VRMs are designed to work with any voltages in the ATX spec range listed above.

I'd start by running Memtest86+ for a few hours to check for RAM going bad. Reseating the GPU card and the cables can't hurt.

Copy that I'll give it a shot !!

5%, spec or not, is some major fluctuation.

Don't worry about the software readings, there's never been a board that has had accurate readings.
Use a digital multi meter.

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Originally Posted by NEOAethyr

5%, spec or not, is some major fluctuation.

Don't worry about the software readings, there's never been a board that has had accurate readings.
Use a digital multi meter.

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The voltage drop if correct is not at all unusual on the 12V rail. Typically there is nothing in a PC other than a HDD, CD or cooling fan that uses full 12V power and these are not voltage sensitive devices. Every critical component on a mobo, CPU or GPU uses lower voltages that are drived from the 12V, 5V and 3.3V PSU rails. The VRMs on those components provide the precise lower voltages and are designed to operate without issue even with the 5% ATX PSU voltage range allowed. The lower voltages are usually held to a +/- 3% tolerance.

http://www.formfactors.org/developer...s%5Catx2_2.pdf

Allowable ATX PSU 2.2 voltage specs link

http://pcsupport.about.com/od/inside...-tolerance.htm

The indicated .34V drop on a lower voltage rail would be out of spec and more critical due to the lower voltages powering the RAM and voltage sensitive circuits which could cause issues but it's highly unlikely on the 12V rail.

The better the PSU quality and design the closer it will hold the voltages but the 2% drop here is not the likely reason for any system instability unless there is something else wrong with the PSU.

Voltage drop under load is normal, and at 11.75v it's well within spec. It's not a problem.

Quote:

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Originally Posted by CrazyNutz

Voltage drop under load is normal, and at 11.75v it's well within spec. It's not a problem.

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Agreed. The component makers all understand that their products must be able to operate with the industry defined ATX PSU voltage range specifications.