How to manually check your desktop computer’s Power Supply Unit (PSU) to know if it’s still working [Troubleshooting Guide]

The Power Supply Unit (PSU) is the main component that powers up your system unit. If electricity is the blood of your computer, then the PSU is the heart as it properly distributes electric current to the motherboard, hard disks, drives, ports, etc. In other words, it’s important that you have a PSU that functions properly to have a system that also runs properly.

A defective power supply may cause a lot of issues; your computer may not power on or your mobo may get fried. So, if your system started to act abnormally, it’s best that you take time checking the power supply to know if it’s still functioning well and prevent further damage. Below is a step-by-step troubleshooting guide you can follow to make sure the PSU of your computer is working properly.

For those who have other issues, however, you can always contact us and tell us more about your computer and the problem so that we can help you find a solution. Fill up our PC issues questionnaire and provide us with accurate information about your machine and the problem. Remember, the accuracy of our troubleshooting guides depends on the information we have. Now, going back to our troubleshooting, here’s what you need to do…

Step 1: Turn off your computer properly. Just because the PSU is acting up doesn’t mean that it can no longer power your computer up. There might be a wire or two that isn’t conducting electricity anymore and causes an unexplained problem. For instance, you may encounter an issue with the hard disk wherein your computer no longer detects it. Obviously, we regard such issue as a “hard disk problem” without looking into the possibility that one of the wires it’s getting power from is no longer delivering necessary voltage to power the disk.

Another issue that might result from having a defective PSU is when the computer no longer powers on. Most of the time, this issue happens without apparent reason and when you least expect it.

After powering off the computer, try to turn it on and if it does, then the power supply unit might still be working fine especially if the computer actually loads up the operating system or, at least, gives you an error. On the other hand, if the computer doesn’t power up, then it’s time you considered a PSU issue. Proceed to the next steps.

Step 2: Unplug the power cable from the wall outlet to avoid electrical hazard. You are about to open up the tower so make sure you, as a technician or owner, are safe from electrical hazard. Aside from unplugging the power cable from the wall outlet, disconnect all cables that are connected to the tower.

Step 3: Remove screws to open up the tower and reveal internal components. You only have to remove one cover (right side) of the tower to access all internal components including the PSU. Once you have removed the cover, touch the part of the chassis that doesn’t have paint to discharge static electricity from your body. You must do this to prevent static from damaging other components.

Step 4: Disconnect all power cables from the motherboard, hard disk, optical devices, etc. Get ready to dismount the PSU by disconnecting all cables attached to other components including the mobo, disks, optical drives and others. Depending on the mobo you’re using, you may have to disconnect two sets of cables the first one being the most obvious 20/24-pin connector and second being the supplementary 4-pin connector.

Step 5: Dismount the Power Supply Unit (PSU) from the tower for easy troubleshooting. While you can troubleshoot the PSU while it’s mounted on the tower, it would be much easier to do so when it’s lying alone on the table. So, remove all screws that connect it to the chassis and carefully and slow dismount it.

Step 6: Check for possible liquid damage or burnt components. It’s always possible that the PSU got damaged by water or any other liquid. I have dealt cases wherein the PSU and mobo got fried due to liquid damage because a mouse found it’s way into the tower and peed. So, try to look or detect water residue.

There are also times due to some unknown reason that one of the components, usually one of the capacitors, get fried. When it’s the capacitor, you can immediately tell due to a foul smell but if it’s a different component, it should, at least, emit burnt smell.

Step 7: Attempt to turn on the PSU. You don’t need advanced knowledge to do this and you don’t need your mobo or tower to switch on the PSU. All you need is something that would serve as a jumper or connector–a paper clip or a short wire with both ends peeled off.

Once you have one of those connectors, find the green wire in the 20/24-pin connector, it’s the only green wire you can find, and then connect it to any of the black wires. You can never go wrong with it since all black wires are ground and there’s only one green wire. Once these two wires are properly connected, the PSU will be powered on once the power cable is plugged into the wall outlet.

At this point, connect the power cable to your PSU and then plug it to the outlet. You can immediately tell if the PSU is still working because its fan rotates but even if it doesn’t, you still have use a multimeter to check voltage output of the wires that commonly gets damaged–yellow, red and orange.

Step 8: Test the output of the yellow, red and orange wires. These wires will give you 12, 5 and 3 voltage readings, respectively. Using your multimeter, connect the black (negative) probe to any black wires and the red (positive) to any of the yellow wires. You get a reading between 13 and 11 volts and anything over 13 and under 11 means there’s a problem. Do the same and take of the actual readings of all yellow wires.

If you’re testing the red wire, you should get a reading between 5.8 and 4.5 volts. If the reading goes over 5.8, there’s chance some of the components or chips in the motherboard will be fried including the hard disk.

As to the orange wire, you should have between 3.6 and 2.9 voltage reading.

If several readings are off, then the PSU needs to be replaced or serviced. This component is the one responsible in powering up your computer so if it doesn’t give out the proper voltage for the components, there’s nothing much you can do but replace it.

Step 9: Mount the PSU back on the chassis and connect it back to the mobo and other components. Assuming you were getting the correct voltage for all the wires, it’s time you checked if it’s capable of powering up your system again. What you did was check if the PSU was doing fine and now that we’ve confirmed that, it’s time to check the mobo.

After you’ve connected all connectors to the mobo, hard disks and other components, try to power on your computer and see if it runs. If it doesn’t turn on, double-check the connections and try again and if it’s still the same, the next step might help.

Step 10: Try to use a different PSU that you know works. While we’ve already checked the other PSU, it’s still necessary to try a different one if possible. So, if the computer still has the same problem, then we can say at this point that it’s really not a PSU problem but probably an issue with the mobo and that’s a different story we’ll have to cover on our next article.

So, to wrap it up, all we did was dismount the Power Supply Unit of your computer, check the voltage readings to see if they conform with normal ranges, after confirming that we mounted it back and made sure all connections are proper and lastly we used a different PSU to rule out, once and for all, that the problem isn’t with the power supply but could be with the motherboard or anything else.

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