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Low -12V


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Just wanted to know if -12V is reading at -7.25V OK? The other reading that is a little low is the +5V at 4.92V. But the main deal is the -12V at -7.25V. I was reading somewhere and they said most motherboards really don't use the -12V much but I don't know if this is true or not. :dunno:

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Thats super low.

I am not an expert by any means when it comes to motherboard / hardware and the PSU.

 

I do know with it only providing 7volts it wont hurt anything but you do run in to the possibility of it not providing enough power to something to where it may not work and cause an error/blue screen.

 

Like Video cards for example if they don't have the power they need, they are not going to work. So maybe right now your hardware is working fine but when you add stress / excessive use to it, it might just shut down on you.

 

Personally I would take that PSU back and get another one. (Different Brand).

 

I am sure more Knowledgeable people will post in here though with some better advise lol!

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No that is fine. I was reading up on it a while back and your -12v is fine if its below that level. Really any of the - readings can be below. What is more important is all the positive readings.

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Strictly speaking the -12V rail shouldn't fall below -10.8V or it doesn't meet the ATX12V V2.3 specification. Having said that I think the only thing it's used for is the now rarely used RS232 serial interface and its derivatives so you may be OK but it could be a sign of power supply failure so my advice would be to get it replaced as soon as possible.

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I'm suprised the pc will even boot if the 12v rail is actually running at 7.25v

 

OP - where are you getting your 12v voltage readings from? BIOS, third party software, or manually measuring with a digital multimeter?

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I'm suprised the pc will even boot if the 12v rail is actually running at 7.25v

 

OP - where are you getting your 12v voltage readings from? BIOS, third party software, or manually measuring with a digital multimeter?

 

 

Note this is the -12V and not the +12V.. +12V seems to be the only that gets used.. This is the one that should be used to power the video card if I been reading right. I looked in my BIOS but it doesn't even show any -V's only +V's. I used some progs in windows and all of them read -7.25v but the ATI overdrive one says it's at -12.68V.. I have not done any manual measuring b/c I don't have the tools anymore.

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How did you obtain your reading?

 

Did you use a multi meter set to volts DC and did you use a 4 pin molex testing between the yellow and a ground black?

 

 

Edit: The only way I can see that you got your reading. would be to test between the two out side pins on a 4 pin molex that would give you a reading of 7v. +12 Yellow to +5v Red this gives you a potential of 7V and the only reason it would be -7v is that your meter leads on the wrong way around.

 

 

4 pin molex

Edited by firky

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Note this is the -12V and not the +12V.. +12V seems to be the only that gets used.. This is the one that should be used to power the video card if I been reading right. I looked in my BIOS but it doesn't even show any -V's only +V's. I used some progs in windows and all of them read -7.25v but the ATI overdrive one says it's at -12.68V.. I have not done any manual measuring b/c I don't have the tools anymore.

 

Gotcha.

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even at -7.25V everything seems to run just fine. I haven't had a problem yet and I been having full loads for hours at a time. None of the rails move much at all from idle to full load.

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When testing power supplies it's very rare for the -12V rail to actually read -12V, it's more often than not hovering around -11.5V at low loads and approaches -12V as the load increases.

 

The only place to measure the -12V rail is pin 14 of the 24 pin motherboard connector so if you have, or can hold of a digital multimeter measure the voltage between pin 14 (blue wire) and any black wire on the motherboard connector. Monitoring the voltage levels in windows via software is very hit and miss, bios is a little more reliable but the only way to be absolutely sure is to measure with a multimeter.

 

Edit: Just had a quick measure.

 

CPUID says 3.27V, 4.95V and 11.85V for my three main rails. Measured at 3.35V, 5.04V and 12.16V. OK not great differences but differences nonetheless. My -12V rail is sitting at -11.8V which is actually pretty good when compared to some power supplies.

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My motherboard BIOS only shows +V and no -V. I have used many different types of programs to see what the voltage is at. All show -7.25V but ATI overdrive one says it's at -12.68V.

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