You can test the voltages in two different places. If
you wish to test your 12v and 5v line and find out what
your components are actually receiving, then you can just
use a molex connector while the computer is still turned
on. If you'd like to also test the 3.3v line, you're going
to have to disconnect your power supply from your computer,
use a wire trick to power the PSU up, and take the voltages
from the motherboard connector. Either way the process
is very simple. You take the negative probe of the multimeter
and push it into a ground. Then take the postive probe
and push it into whatever line you want to test.
We'll start off with testing
the PSU's motherboard connector. First things first, unplug
all the power connectors from your computer. Then, grab
a piece of wire (we used a piece from a model train layout)
and connect the green wire to the black wire next to it,
as seen below. Once done sucessfully, flip the power switch
on the back of the PSU and you should hear the fan start
Here's a diagram of what each wire is.
Then, take your multimeter and push the
negative (black) probe into any one of the GND wires.
Take the postive (red) and push it into whichever line
you would like to test (3.3v, 5v, 12v). Your multimeter
will then give you a readout of precisely what the voltage
in that line is.
There is one major flaw
in this technique, nothing is drawing power from the PSU.
So, the voltages that this will give you aren't necessarily
what your computer parts are receiving. However, this
will let you know if your PSU is capable of supplying
the correct amount of voltage, and will also ensure that
it is not defective.
Now, it's time to check
what our components are actually receiving. While the
computer is on, grab an extra molex conector. This time,
the ground wires are the two in the middle, the 12V is
the yellow wire, and the 5V is the red wire. Put the negative
(black) probe into either of the grounds, and the positive
(red) probe into either the 12V or 5V plug. This will
give you a reading that will show you what voltage each
component that runs off that line in your system is actually
Below are some shots of
this technique in action. As you can see our voltages
are almost right on.
In the end, you'll have
a good idea of how well your power supply truely delivers.
Please remember as I said before, I suggest anyone who
tries this to be careful. Electricity isn't something
you want to play with, and we are not responsible for
any harm you may cause.