Power Supply Voltages

A friend of mine bought a new PSU, a 550w ThermalTake if I remember correctly. The PC runs fine, everything is stable and OK, it turns off and on without issues, but the reading for -12v is WAY off. Both the BIOS and HWMonitor read the -12v at -7.81v. The power supply is only about 2 months old (it's been doing this from day one) and still covered by warranty. Is this something to worry about, should he exchange the PSU or is it not a big deal???

 

Something is not right.Look at this:http://www.techniz.co.uk/component/content/article/314?start=2
or
http://www.newegg.com/Product/Product.aspx?Item=N82E16817153029
I found two thermaltake PSU's with 550w.

 

So measure the -12V rail with a voltmeter.

The standard is+/- 5% which I see is quoted in Goran's link.

 

Thanks for the info. I will try to get in there with a voltmeter, but I'm pretty sure that if both the BIOS and HWmonitor are reading the -12v rail the same, they're probably right. If the BIOS reported -12.10 and HWmonitor reported -6.42 then I'd think that something was amiss, but both report the same readings. What I want to know is: can he safely continue to use this power supply? Is there a chance it could damage his hardware? Personally, I told him to exchange it. It is not normal for a PSU (esp only 2-3 months old) to be reading that far off. I said it doesn't really matter if it's causing a problem or not, or if it could potentially cause a problem, it isn't right - it shouldn't be doing what it's doing and since it is under warranty, return it. But he's reluctant 'cuz he bought it online (I don't know where) and knows it will be a major-league pain to ship it out and wait, plus there's the downtime whilst waiting for the replacement. But, is there any risk of damage from use of this power supply?

 

Everything that is abnormal can damage the mobo.Maybe not now ,but I think that you are clean now cos you tell him to return the PSU back.I don't know what this rail(-12v)supply on the mobo.DLB,can you replace this PSU with another one ,and see if the measurement is right?

 

Yup..... I was already thinking about it. I have a no-name 680w that I know is good, so I'll check that out and see what's up.

 

A low negative 12 volt rail won't damage the motherboard. It is not much used anyway, and often cut down by internal regulators.

It was used for the old serial (RS232) interface, modems and the like for signalling purposes.

If this rail is too low these interfaces will be unreliable.

 

Great info. I have passed this along to my friend in an email. I know he doesn't use a modem as he's got ATT DSL, and I don't know what else would use RS232 besides maybe something plugged into the serial port, and I'm pretty sure that he doesn't have anything serial either.... who does these days? The only serial devices that even come to mind are the old, really old ball mouses, old digital cameras, and really, really, really old dial up modems, like 14.4 and slower. Yeah, I know, USRobotics still makes a 56k serial modem, but who the heck is going to buy a dial-up for like $60??? Anyway- I'm rambling here. Too much freekin' coffee on this fine Sunday morning. Thanks for the info... it has been passed to the dude who needs it. He'll be glad as he really didn't want to deal with uninstalling and the downtime and the overall hassle of a warranty return.

 

I use R232,to connect my addpack (Voip) for manualy settings.
Studiot thank you for the info(I learn something).

 

The +/- 12 volts swing is in the RS232 spec but many early home computers didn't used to achieve this. The Commodore and Sinclair in particular. +/- 9 was common or even 6.
This is usually OK when interfacing with local devices esp ones with CMOS inputs.
Hoever it must be the full 12 when interfacing with the Telephone network.