Question about checking PSU output with a Multimeter

[Ilmater]

I would like to make sure that my PSU is putting out what it's supposed to, so I was wondering if some in here could help. I have a few questions:

Which wire (yelow or red) is the 12v wire? I think it's the yellow, but I don't remember.

Do I have to connect the black multimeter pole to the black wire next to the respective colored wire on the molex connector, or do I just need to connect the red pole?

I assume I have to check these outputs when the computer is on, but are there any precautions to take?

Any and all help is appreciated.

[RotorHead]

The yellow wire is 12V, the red wire is 5V.

Just take the black lead from your multi meter and connect it to a black wire on the connector, then connect the read lead on the meter to either the yellow to check 12Vor to the red wire to check 5V. :)

RH

[Ilmater]

Thanks for the help. I got between 12.14v and 12.17v on the 12v rail, and 4.95v and 4.97v on the 5v rail. I don't know how good that is, but I think it's acceptible.

[RotorHead]

I think you’re doing fine with those readings. I’ve always used the 3% rule so it looks fine to me.

It’s definitely a good idea to check your power like that because you can compare them to your BIOS readings. If they’re off, then you’ll know the difference. :)

RH

[KingTermite]

Those readings sound ok. Remember...even the Multimeter has probably a 2% or so error.

If you wanted to really get fancy...you could hook the MM up to the computer (if its any of the newer ones with software and RS-232 (or maybe USB nowadays) connections) and let it monitor all night and store min/max values.

But if your readings are that close...I wouldn't take the time even if you Multimeter did have that capability.

[Ilmater]

Originally posted by KingTermite
Those readings sound ok. Remember...even the Multimeter has probably a 2% or so error.

If you wanted to really get fancy...you could hook the MM up to the computer (if its any of the newer ones with software and RS-232 (or maybe USB nowadays) connections) and let it monitor all night and store min/max values.

But if your readings are that close...I wouldn't take the time even if you Multimeter did have that capability.
It's a $20 MM. It doesn't hook up to anything but a battery and two posts.

[Razorback]

Originally posted by KingTermite
Those readings sound ok. Remember...even the Multimeter has probably a 2% or so error.

If you wanted to really get fancy...you could hook the MM up to the computer (if its any of the newer ones with software and RS-232 (or maybe USB nowadays) connections) and let it monitor all night and store min/max values.

But if your readings are that close...I wouldn't take the time even if you Multimeter did have that capability.

If you want to get fancier, get an oscope and check to see how bad your voltage ripple is. New digital multimeters are nice but their sampling sometimes isn't good enough to see how good your power truly is. A case in point: I had a control network that required tight control on the 24 VDC power. From the MM's perspective, everything was OK but when checked w/my oscope, w/appropriate triggering, I found the voltage dropped to 11 VDC which was wreaking havoc on the communication signals.