Whenever you upgrade your system or build a new system with an old power supply, you should always check the power supply to make sure . It’s also good to check in once and a while to see if your power supply is still running your system well or needs replacing. The best way to see if your power supply is doing its job is to check the voltages. To do this you can go down to routes, using software or testing it with a multimeter. Since we at HardwareLogic always want the most accurate numbers, my special assistant Bobby and I are going to teach you how to do it with a multimeter. Using a multimeter will give you the most accurate numbers while using software will give you numbers that will be off.
What are rails and Where should they be at?
Before we go and test our power supply, you should know what exactly rails are and what each one does… So… Bobby… do you know what a rail is? No sir. I didn’t think so. Well, rails are the voltage lines coming from your power supply. There are only 3 voltages that you need to know about. The 12V rail, 5V rail, and 3.3V rail. The 5v and 3.3v rail generally power devices like your motherboard, and its onboard peripherals. The 12v generally powers hard drives, CD drives, fans, etc. Many new motherboards draw from this line as well.
I have one more thing to go through before we start. What were going to do involves electricity. That means that you have to take extreme caution or you may wind up shocked and on your ass. HardwareLogic and I cannot be held responsible for anything that happens to you, others, or your system.
If you aren’t sure what your doing, Don’t do it.
Getting the Numbers
In the above picture is a Digital Multimeter. You can use an analogue Multimeter but it might not be as accurate and harder to use. The digital multimeter I will be using reads out to two decimal points.
If you plan to get load voltage readings it is strongly advised to download a stress testing program such as Prime95 before shutting down your system. You can download Prime95 here: http://www.mersenne.org/freesoft.htm. To gaurentee that your power supply can run your system it is necessary that you run it all full load to maximize power consumption.
Now comes the fun part! Power down the computer and lay it down on its side. You can get a reading from the ATX main connector or the molex connector but�today we're going to show you how to get a reading from the main ATX connector first. The system draws its main power through here, therefore you will get the most accurate numbers. The power running through the Molex connectors is peripheral power. Its good to know exactly what your going to be testing. We’ll be testing the 12v, 5v, and 3.3v as I mentioned above. To help remember which wire is which rail, think alphabetical order. Orange wires are 3.3 volt, Red wires are 5 volt, and Yellow wires are 12 volt.
Make sure your system is turned off.Take the multimeter and put the black rod into any of the grounds. All of the grounds are colored black. Push the rod far enough to get good contact with the metal lead inside. Remember, you want to make contact with the actual wire not the plastic wire covering. Depending on which rail you want to test, you can put the red rod in either the Orange, Red, or Yellow wires. Boot up the system and make sure none of them get loose and fall out, the results could be disastrous.
To get an idle voltage, leave your system idle for a minute or two then check the multimeter readout. To get the more important load voltage, start your stress testing program or Prime95. In Prime95 run the torture test, this will make your system run at full load. Let it run for a minute or until the voltages balance out. By the way, make sure your multimeter is set to DC or Direct Current otherwise you won’t get the right numbers.
Now for the Molex Testing Method. This method is much easier and may be less of a frightening experience. Again, make sure your system is on its side. Grab a free molex and lay it on a non-conductive surface. One downside for this testing method is you only have access to the 5v and 12v rails.
Remember, Yellow is 12v, Red is 5v, and Ground is black. To get a reading, put the black probe into either of the grounds and the red probe into whichever rail you want to test. The rest is the same as the ATX method.
Voila! Your done. Using this method you can accurately measure your voltages and determine whether your PSU is capable of running your system or not.
