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Using a Power Supply Tester
February 02 2008

As anyone who has ever built their own system can tell you, their comes a "moment of truth" so to speak, when you hit that power button on your PC for the first time. No matter how many times you have done it before, or how good the equipment is that you are using... there is always a margin of error/failure which can creep up on you and smash your new PC dreams. While you can minimize your risks by using quality hardware from a reputable manufacturer, there is always the chance that the piece of hardware could have been damaged during shipment as well as a myriad of other possibilities.

There is a way to further increase the likelihood that your new PC will fire up that first time, though. Test the power supply! A properly working PSU will fire that new rig up and you will be off and gaming in no time. However, a bad PSU will set you back until you are able to secure a new one... a REALLY bad PSU could even end up killing other parts of your PC. I know this because I have been a victim of such a catastrophic event. Checking out the PSU with a PSU-tester before hooking it up can save you time, money & stress. When you consider these points, the $15 - $30 cost of a tester seems pretty trivial and the first time you run across a PSU that fails the test, you have virtually paid for the tester many times over.

Testing a PSU using one of these devices is a quick and painless task. For this article I will be using a modified PC Power & Cooling PSU shown to the left. The PSU tester I am using both come from FrozenCPU including a standard LED-only model (~$15) and a model with a more informative LCD display (~$28). First, here is the basic testing procedure: First, make sure that the switch on your PSU (if it has one) is turned to the "Off" position. Connect the main motherboard wire bundle (20 or 24 pin) to the tester and then plug the PSU into a power source. When you turn on the PSU the tester should quickly light up and show you which voltage tests are within specs. From this point on you should only connect one other line at a time. Plug-in, read, unplug... this is repeated until all lines (or all plugs) are tested to your satisfaction. The pics below will show you what to expect on a good test; I had to take the pics in low light so that you could easily see the test results.


20 & 24 Pin (Main Motherboard bundle)

When you first fire up the PSU the tester should greet you with a quick beep which means that everything is ok. If you don't hear a beep, then something did not check out right. The LED row along the right show results for +3.3V, -12V, PG (Power Good meaning that overall the PSU test was good), +5VSB, +12V, -5V, & +5V. Don't be alarmed when testing your new PSU if the -5V LED does not light up. If you are testing an ATX PSU that adheres to version 1.3 or higher for PSU Specs, the -5V LED may not come on since the spec for -5V was removed because it was only used by, now non-existent, ISA cards. On the LCD version you will see a PG Value which is the time, in milliseconds, from turning on the PSU to when the voltage is actually sent.

PSU Tester Motherbaord Bundle - Standard PSU Tester Motherbaord Bundle - LCD


8Pin & 4Pin Motherboard Power

Plug in the 8pin or 4pin motherboard power connector and you should see the +12V LED on the left hand side light up. If you are using the LCD model, the +12V2 rating will display.

PSU Tester 4Pin/8Pin Motherboard Power - Standard PSU Tester 4Pin/8Pin Motherboard Power - LCD


Floppy Power Connector

For the Floppy connector the +12V and +5V LEDs will be lit up along the left hand side of both PSU tester models.

PSU Tester Floppy Power - Standard PSU Tester Floppy Power - LCD


Standard Molex

The Molex Connector (located along the bottom edge of the tester) should give results similar to the Floppy connector. A lit up +12V and +5V LED.

PSU Tester Molex Power - Standard PSU Tester Molex Power - LCD


PCI-E (Video Cards)

Using the middle connector group along the left side of the testers to test the 6Pin PCI-E (video card) power connectors will give you a +12V2 rating on the LCD tester and a lit up +12V LED on the left side of the standard tester.

PSU Tester PCI-E Power - Standard PSU Tester PCI-E Power - LCD


SATA Power

The SATA power connector is located along the top edge of both testers. When you test this connector you should see all three LEDs along the left side of both units light up; these represent +12V, +3.3V & +5V tests.

PSU Tester SATA Power - Standard PSU Tester SATA Power - LCD



The tester did not beep and/or the xxxV test light did not light up! Now what?

Well, as was mentioned earlier, If you are testing an ATX PSU that adheres to version 1.3 or higher for PSU Specs, the -5V LED may not come on since the spec for -5V was removed because it was only used by, now non-existent, ISA cards. If it was a different LED indicator or rating then make sure that you test all connectors along that string (if applicable) to determine if it is just a problem with that particular connector or the entire line. If it is a problem with the entire line then it that can be indicative of a failing, or already failed, PSU. Check your PSU's warranty and make plans to replace it ASAP.


Please Note: Do not leave the PSU tester plugged into a PSU for a great length of time and do not leave them unattended. They can generate heat and are not intended to be plugged in for an extended duration. They are intended to be used as a quick means to evaluate a PSU's health and reliability.