PDA

View Full Version : Measuring the rails on PSU's

TheLostSwede
9 Feb 2005, 10:35pm
Just a little guide to show how easy it really is if you think your psu might call it a day.

The 12V rail. Note how the multimeter is set. Look at the symbol to the right of the actual know as that can be on different places on different multimeters. The red pin goes to the yellow connector on the Molex and the black pin to the black connector on the same Molex. (Or any ground at all)
TheLostSwede
9 Feb 2005, 10:36pm
The 5 volt line.

All you have to do is change the red pin to the red connector on the molex.
TheLostSwede
9 Feb 2005, 10:41pm
Finally the 3.3V line.

There are 2 ways to measure this. The easiest is on the AUX connector. You should look for an orange cable and its connector. That orange cable is also on the ATX connector if you find it easier to measure that. The red pin should go to an orange cable and the black pin to any black cables. (Molex or the atx will do fine)
MediaMan
10 Feb 2005, 1:18am
Just a little hint for anyone who goes probing with a multimeter on the fly with a live system...make sure you plug the ground in first before connecting the hot line.

If you plug the hot line in...and forget where you left the black ground probe...sitting there on the metal of your case...

*pop*

Your system will short and shut down real quick. Now you'll probably be lucky and nothing will happen except a moment of panic where you thought you toasted your system....but just in case...be aware of what you are doing.

/me speaks from experience.


Thanks for the tips Mac! :)
bothered
10 Feb 2005, 11:07am
Just a little hint for anyone who goes probing with a multimeter on the fly with a live system

To get a real reading the PC would have to be running. The 'no load' voltage could be higher than when under load if the PSU isn't coping.
Geeky1
10 Feb 2005, 11:13am
Mediaman... I just tried that... didn't do anything on my xeon system. I think you might have a faulty multimeter. :-/
muddocktor
10 Feb 2005, 3:32pm
Geeky's right, MM. Unless you have the meter set on ohms or amps, you shouldn't see any fireworks with the common lead touching the case. After all, the case should be at ground potential and be grounded to the psu via it's attachment screws. Now if the VOM is set on ohms or amps, you will definitely see fireworks. ;)