How to Test Your Computer’s PSU With a PSU Tester





A PSU tester resting on a PSU.
Jason Fitzpatrick / How-To Geek

A PSU tester is one of the simplest ways to test your computer’s PSU as it offers an all-in-one experience with immediate actionable feedback.

Why Use a PSU Tester?

PSU testers are so cheap and so easy to use that we really can’t recommend them enough. If you have a multimeter, you’re comfortable using it, and you don’t mind testing a bunch of pins and taking notes, you can certainly test your PSU the old-fashioned way.

But, besides the simple plug-and-play ease of using a PSU tester, it has one significant benefit over doing the test manually.

A PSU tester is purpose-built for the task and will give you both immediate feedback on whether or not the connections match the expected voltage and configuration or not as well as loudly alerting you if they do not.

Further, it allows for easy SATA terminal testing (there’s no way to easily test the tiny pinout on a SATA connector with a multimeter) and it will give you a readout for the PG value—the “power good” time-to-start delay period—that a multimeter cannot.

Finally, a word on PSU testers: they all look just about the same because they are all just about the same. There are dozens of brands that look just like the model we recommended above because basic PSU testers are a “white box” product.

A few factories crank out a bajillion of them, and different companies pay to have their particular case and/or logo slapped on the circuit board. But inside, they’re identical. Should you be reading this article and the specific PSU tester we linked to above (and are using for this tutorial) is out of stock, you can simply buy another that looks just like it, such as this one or this one.

How to Use a PSU Tester

Using a PSU tester is straight forward, but you should always follow best practices. Here’s how to test your PSU safely with a tester.

Warning: At no point will we be opening up the PSU itself. Doing so without proper precautions, knowledge, and tools can give you a lethal shock.

Before Testing your PSU, Disconnect the Cables

Power off your PSU. If it has a switch, you can use the switch on the back. Otherwise, unplug it. Before using the PSU tester, we recommend unplugging not just the particular cable you wish to test but all the cables linking your PSU to internal components.

Not only will this protect the various components if anything should go wrong, but it’s wise to test every cable at once to ensure the PSU is functioning properly across the board.

Attach the PSU Tester and Power Up the PSU

The PSU tester draws power from the PSU itself. To use it, simply turn off the PSU (either with the switch on the back or by unplugging it from the wall).

Then plug in the mother power cable to the tester as well as the CPU power connector cable—if you don’t plug in the CPU cable, you’ll get an error message. Turn on the PSU.

Reading the PSU Tester Results

The tester will show you various power categories it expects from the motherboard and CPU cables like -12V, +12V, +3.3V, etc. Beneath those categories, it will show you the actual voltage.

It’s OK if these values don’t match up exactly. If the -12V value is 11.8, that’s well within the expected ±5% range acceptable for that connection. And if it were outside the range, the tester would warn you—no math or knowledge of the acceptable range required.

It will also show you the PG value. This value represents how long it took your PSU to go from the first sign of power activity to full voltage across all connections.

An acceptable value is 100-500 milliseconds. A higher value can indicate failing PSU components, and an excessive PG value can cause your computer to get stuck in a boot loop because your hardware components don’t power on in the expected window.

You can further test other connections, including the PCI-E, MOLEX, SATA, and 4-pin floppy connector, to ensure each connection delivers the expected output.

Most testers, including the one here, have a simple LED light indicator for the voltages when testing the secondary cables. Because of that, you need to test the cables one at a time (e.g. don’t plug in a SATA cable and a MOLEX drive connector simultaneously).

It won’t hurt the tester or the PSU, but you won’t get an accurate readout for their respective voltages because there is only one set of LED indicators.

If your PSU tests indicate that the expected voltages are out of spec (e.g. you get 8 volts for one of the connections when 12 is expected) or your PG value is over 500 milliseconds, it’s time to replace your PSU.





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