Introduction: How to Test and Replace a Power Supply for Your Home Computer

I created this Instructable because power supplies in home computers fail quite often and they can easily be replaced. I have written this instructable so that basically anyone that uses a home computer can follow these step by step instructions to test and replace their power supply if they need to. By doing this yourself, you can save money by not having to pay a computer technician to do it for you.

In most cases when a power supply fails nothing happens when you go to turn on your computer, as if it were unplugged from the wall. Once you have checked to make sure it is plugged into the wall and should be receiving power. If nothing continues to happen when you turn on the power, you might consider testing your power supply and replacing it yourself.

In this Instructable I will show you how to test and replace a power supply for your home computer. I will be using an ATX  Mini Tower Case which is the most common used for home computers.

Step 1: Tools and Parts Needed

To test your power supply you will need a multi-meter and a Phillips head screwdriver. You will also need a new power supply to replace the old one.

Step 2: Testing the Power Supply

The following steps will show you how to test your power supply.

Step 3: Open Case

First you will want to shut of the computer and remove the left side cover on the case. Start by selecting the start button on the bottom left of your windows desktop screen and left clicking the shutdown button. Once this is done, unplug the power cord from the top left side of the power supply. You will now use a Phillips screwdriver to remove the 2 screws from the rear of the computer that are holding the left side panel in place. Now remove the side panel. 

Step 4: Unplug the Power Connectors

Once you have done this you will want to disconnect all the power connectors from the devices in the computer except the P1 10x2(20 pin) from the motherboard. You will need it connected to turn on the power supply. You can test the power supply with it still plugged in. On newer motherboards there will be an extra 4 pins (2x2) for a total of 24 pins and ones that support PCI express will usually have a 4x1 connector to supply additional power to video cards through the motherboard and that will need to be disconnected if applicable. Start out by disconnecting the large 4 pin (4x1) molex from the CD/DVD drive and the large 4 pin (4x1) molex from the (IDE) hard drive. Then disconnect the 4 pin (2x2) molex plug from the motherboard and the 6 pin (3x3) molex plug from the video card.

Step 5: Setting Up the Volt Meter

Now that all the plugs are disconnected except the P1 you can plug the power cord back into the power supply. You can start by turning on your multi-meter and testing it. Set it to 2000k ohms and hold the 2 probes apart. You should get a reading of 0. Then touch them together and you should get a reading of 1. If it is working correctly set it to 20 DC volts. This way you are setting it as close to, but greater than the voltage you will be testing. Since the computer devices use a maximum of 12 volts 20 is the best option.

Step 6: Testing the Molex Plugs

Start by grabbing a large (4x1) molex plug and insert the black probe into one of the black (ground) wires on the molex plug. Then place the red probe into the red wire for your reading. Since this is a red wire, it is a 5 volt wire and should read somewhere in the range of 4.5 to 5.5 volts. Now remove the red probe from the red wire and connect it to the yellow wire while leaving the black probe where it is in the black (ground) wire. The yellow wire is a 12 volt wire and should read somewhere between 10.8 volts and 13.2 volts. Repeat this process for each of the molex plugs including the 4 pin (2x2) molex plug and the 6 pin (3x3) molex plug coming from the power supply.

Step 7: Testing the P1 Plug

Now to test the P1 (10x2) 20 pin plug you will want to slide the black probe into one of the black (ground) wires in the back of the P1 plug while it is still connected. Make sure it goes down far enough to make contact. Once the ground is in place you can leave it there while we test the other wires. Start by testing the orange wire by placing the red probe into the back of the P1 plug where the orange wire is. Since the orange wire is a 3.3 volt wire it should read somewhere between 3.0 volts and 3.63 volts. Now test the blue wire by removing the red probe from the orange wire and sliding it into the P1 plug where the blue wire is. The blue wire is a (negative) -12 volt wire and should read somewhere between -10.8 volts to -13.2 volts. Then place the red probe into the red wire. Once again since this is a red wire, it is a 5 volt wire and should read somewhere in the range of 4.5 to 5.5 volts. Now remove the red probe from the red wire and connect it to the yellow wire. The yellow wire is a 12 volt wire and should read somewhere between 10.8 volts and 13.2 volts. Once you have finished testing remove the probes from the P1 plug and turn off your meter. Then turn off the power supply by using the switch on the back of the power supply by turning it to the off position and don’t forget to unplug the P1 plug from the motherboard. At this point, if you have determined that your power supply is not working properly you will want to replace it.
If your power supply is still good you will need to reconnect everything and make sure the computer boots up fine and still works.

Step 8: Reconnecting the Power Connectors

Start disconnecting the power cord from the back of the power supply. Then reconnect the P1 to the motherboard along with the 4 pin PCI express plug and the 6 pin molex plug to the video card. Now reconnect the large 4 pin molex plug to the (IDE) hard drive. Reconnect the large 4 pin molex plug to the CD/DVD drive. Once all the devices are plugged back in, place the cover back on the case and screw it back into place with the 2 screws you removed earlier. Then plug the power cord back into the power supply on the back side of the computer. Now you will turn the computer back on by using the power switch on the front of the computer. Watch for the green power light to go on. You will also want to listen and feel for the fan in the power supply and the (IDE) hard drive to start up. If everything was done correctly the computer should boot up into windows.

Step 9: Replacing the Power Supply

The following steps will show you how to replace the power supply.


Step 10: Disconnecting the Power Supply

When replacing a power supply one of the first things you want to do is unplug the computer from the wall and remove the power cable from the back of the computer/power supply. Once this is done, you will open the case to your computer. Here we are using a standard mid tower case and will only be removing the left side to access the computer. You will need a Phillips screwdriver to do this. Now remove the 2 screws that are holding the cover in place on the left side and slide it off. There are lots of different cases out there please refer to you case documentation if you are having trouble. Now that you are inside the case, unplug all of the power cords that are plugged into the motherboard and other components. Start out by disconnecting the P1 (10x2) 20pin plug. On newer motherboards there will be an extra 4 pins (2x2) for a total of 24 pins. Then disconnect the 4 pin (2x2) molex plug from the motherboard and the 6 pin (3x3) molex plug from the video card. Now disconnect the large 4 pin (4x1) molex from the CD/DVD drive and disconnect the large 4 pin (4x1) molex from the (IDE) hard drive.

Step 11: Removing and Replacing the Power Supply

First remove the 4 mounting screws that are holding the power supply in place. (Figure 6)

After removing the mounting screw you will simply lift out the old power supply and replace it with the new one. (Figure 7) Once it is seated properly, replace the 4 screws back into the back of the power supply and case.

Step 12:

Now that the power supply is mounted in place we will reconnect all the power supply connectors back to the motherboard and other devices. Start out by reconnecting the the P1 to the motherboard along with the 4 pin PCI express plug and the 6 pin molex plug to the video card. Now reconnect the large 4 pin molex plug to the (IDE) hard drive. Reconnect the large 4 pin molex plug to the CD/DVD drive.

Step 13: Bundle Up Extra Cconnectors

Now that all the devices are connected it is a good idea to bundle up all the extra connectors and move them out of the way so that they don’t interrupt air flow through the case or touch any of the moving parts on the fans. (Figure 13)

Step 14: Replace Cover and Power Up the Computer

Once all the devices are plugged back in and the wires are bundled, place the cover back on the case and screw it back into place with the 2 screws you removed earlier. Then plug the power cord back into the power supply on the back side of the computer and turn the power switch back on that is just under it. Now you will turn the computer back on by using the power switch on the front of the computer. Watch for the green power light to go on. You will also want to listen and feel for the fan in the power supply and the (IDE) hard drive to start up. If everything was done correctly the computer should boot up into windows.

Comments

author
jscanlan (author)2013-12-08

Before you buy a power supply confirm the type you will be replacing. AT does not equal ATX and some machines need additional connectors for Video and or SATA devices. Some of the bargain PSs are way out of date.

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