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Testing PSU Voltages

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 running.

Here's a diagram of what pin is what line.
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.

You can also use a paperclip if you don't have any wire, but I don't suggest that. There's a lot to hold onto, ask someone to help if you need it.

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 receiving.

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.

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