Computer Repair

A digital multimeter has many different settings to help diagnose electrical problems.
The power supply on a computer transforms the alternating current from the wall outlet into a direct current flow that the computer's components can use. Testing the DC voltage output of the power supply using a digital multimeter can help you isolate any potential issues and determine if you have a bad power supply. Always use the probes to touch wires and terminals -- never use your fingers. If you can't hold the wires or terminals with the probes, use a stand or binder clip to secure them so you don't have to hold them with your hand.

1.
Test the outlet and surge protector into which the power supply has been plugged. Power off the computer, unplug it from the surge protector, and then unplug the surge protector from the wall outlet.

2.
Set your digital multimeter to measure AC voltage. The AC symbol is a "V" with a "~" near it. Set it to the range of 200 V. Insert one probe into the left side of the outlet and the other into the right. Since the current is alternating, the probe color doesn't matter. You should see a reading of between 110 and 120 volts.

3.
Plug the surge protector into the outlet, and then test the surge protector. The reading should still be between 110 and 120 volts.

4.
Set your multimeter to measure resistance; the symbol is "Ω." If there is a symbol on your dial that looks like an arrow pointing to sound waves, use that one. The multimeter makes a sound if there is continuity along a wire. Remove the cord connected to the power supply on the back of the computer. Touch one of the plug terminals with one of the DMM probes. Put the other probe into the female end of the cord. If none of the holes produce a tone on your multimeter, then the cord is bad and needs to be replaced. If you have continuity for each of the three wires in the power supply cable, then there is an issue with the power supply.

5.
Remove your computer's case, and then locate the place where the power supply attaches to the motherboard. The ATX style power supply won't operate unless it is connected to the motherboard, so you must insert the probes into the back side of the connector to make contact with the wires.

6.
Note the orientation of the clip that secures the connector to the motherboard; the clip is between pins 15 and 16. The pins on that side are 11 through 20, and the pins on the opposite side are 1 through 10. Power is carried through pins 1, 2, 4, 6, 9, 10, 11, 19 and 20. Use a pin diagram to identify the different testing locations (link in Resources).

7.
Set the multimeter to read DC voltage. The symbol is "V" and a straight line over a broken line. Set the range to 20 volts.

8.
Insert the black probe into the back of the connector with any black wire. Insert the red probe into the back of pin 10. Power on the computer. The multimeter should read between 11 and 12 volts. If it's too high or too low, the power supply is failing and needs to be replaced. Test pin 12 as well.

9.
Test pins 4, 8, 9, 19 and 20 for 5 volts. If the voltage is too high or low, the power supply is failing.

10.
Test pins 1, 2 and 11 for 3.3 volts.

Warning
Don't attempt to salvage or repair a failing power supply, as doing so may damage your computer.

If your PC is refusing to work with another piece of hardware, or running into problems when booting up, you may need to update or change your BIOS to correct the issue. Here’s a step-by-step guide on how to make changes to get your computer working.

Related: How to reinstall Windows 10

What is the BIOS?
The BIOS (or Basic Input Output System) is the very first thing your computer reads when you switch it on. It’s located on your PC’s motherboard, away from the rest of the system disks, so it won’t be corrupted if your hard drive fails.

This firmware’s primary function is to get your computer up and running, by initialising the hardware and then loading up the operating system (OS). The BIOS checks your processor and memory is present and correct, while also detecting which peripherals (keyboard, mouse and so on) are attached to your PC. Following that, it checks to see if you’ve inserted a boot disc. If none is found, it loads the OS into memory and gets things started up.

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Should I make changes to the BIOS?
Tinkering with your BIOS can help to rectify any severe problems that your PC is experiencing, if you can’t actually boot into Windows to make changes there. As long as you know what you’re doing, of course.

Likewise, updating the BIOS with the latest version can allow your computer to play nice with new peripherals and hardware, which previously weren’t supported.

However, and we can’t stress strongly enough, playing around inside of the BIOS settings without the proper knowledge can lead to serious anguish. As in, your computer may be completely borked if you improperly change any of the settings. So if you’re having issues with your PC booting up or not recognising new peripherals and you’re not experienced in this area, you should consult a technician instead of throwing yourself blindly into the abyss.

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What should I do before making changes to the BIOS?
If you’re working with a laptop, then make sure it’s plugged in and the battery is at least half charged. If the power suddenly cuts partway through the update process, then things could get very ugly indeed.

Before starting you should also check which BIOS version you’re using, so you can find out if a newer version is available from your motherboard’s manufacturer.

How do I check which BIOS version I’m using?
The easiest way to do this is using the Windows Command Prompt. In the search box at the bottom left corner of your Windows desktop (beside the Windows start button), type in ‘cmd’ and press enter. A command window will pop into existence.

In here, type the following: Wmic bios get biosversion

Some text will pop up, revealing the current version number.

Alternatively, you can open a command window in the same way and type in: DXDiag

A DirectX Diagnostic window will appear on-screen. Beside the ‘BIOS’ entry in system information, your current version will be listed.

Once you know your BIOS version, you can then check on your manufacturer’s website to see if a newer version can be downloaded.

How do I update my computer’s BIOS?
To download the latest version, you’ll need to head to your motherboard manufacturer’s website (on a different computer if your own refuses to boot, of course). If you’re not sure of the make and model of the motherboard stashed inside of your PC, and your computer manuals have vanished into the ether, then you can always use a tool such as CPU-Z – again, assuming your PC actually functions.

On the manufacturer’s website, head to the downloads or support section and search for your model number. You should see the option to grab the latest BIOS edition, which will often download as an executable Windows program. Once this program has downloaded, you can simply run it from within Windows. This will wipe the BIOS and replace it with the latest info. Again, take every precaution to avoid losing power, as this could critically harm your computer. Also, note that you may need to disable your antivirus and security applications if the program fails, before running it again.

Alternatively, your manufacturer may provide a program to create a bootable flash drive. Download this from the website as above, but this time you’ll need to provide a USB stick or other external drive with enough space to hold the necessary files. Make sure the drive doesn’t have anything important on it, because it may be wiped in the process.

Connect it to your PC and run the program you just downloaded, and the files will be copied onto the external drive.

Now you’ll have to reboot your computer with the external drive still connected. Press F12 when the PC begins to load and you’ll be asked for a source. Select the external drive and then simply follow the on-screen instructions to update the BIOS.

How do I make changes to my BIOS?
If you wish to make direct changes to your BIOS, for instance to change the boot up checking sequence to load an OS from disc instead of the computer’s main drive, then you’ll need to go into the BIOS and fiddle with it directly. You can do this as your computer first boots up.

As soon as you hit the power button, you’ll see some text flash up on your monitor. One of these lines of text will tell you what key to press in order to enter the BIOS. It’s usually the Delete key, but this may differ depending on your motherboard.

A menu will appear offering a variety of options and settings. Remember, only make changes if you’re absolutely confident that you won’t cripple the computer.

The motherboard might not be the most exciting part of your system, but it’s arguably the most important. It’s also the biggest, which can make it a bit awkward to install, but as long as you’re careful it’s not difficult. Whether you have a mammoth eATX board, a more typical ATX, or one of the smaller mATX or ITX options, here’s how to install a motherboard in a few quick steps.

If you’re still on the fence about what motherboard to buy, here are some great options for gamers.

Step 1: Prepare your toolshow to install an amd processor buildingpcs01
Before you install any PC component, it’s important to get all the tools you’ll need and adequately protect yourself and your hardware. That means wearing an anti-static wristband and performing the installation on a non-conductive surface — definitely don’t do it on a carpeted floor.

In the case of a motherboard, you’ll want a long, Phillips head screwdriver, preferably one with a lightly magnetized tip to hold the screws to it. A pair of needle-nose pliers is a good idea too, should you need to fish out any screws that are dropped within the bowels of your PC case.

We’d also recommend good lighting so that you can see what you’re doing and make sure to have your motherboard manual handy if you have any questions that are specific about your board.

Step 2: Screw in the standoffsMotherboard Standoff
A motherboard is a sensitive piece of electronic equipment, so we don’t want it to come into contact with the conductive chassis of your case. That’s why, before installing the motherboard itself, we need to install the standoffs. They are male screws with a female head, letting you screw the motherboard into them directly. They are often brass, but are sometimes painted black. You should have received a number of them in a small bag with your motherboard, or alternatively, with your case.

Many cases come with these pre-fitted, but not always for the specific form or size of motherboard you’re using.

Refer to your motherboard and case manual (or look for eATX, ATX, mATX, or ITX notes on the motherboard tray) to find out which ones you need to screw in and where. When you’ve found the correct locations, screw them in by hand. It can be a little fiddly, but you shouldn’t need to use any kind of tools to get them in. If you feel the need to, it’s usually because the standoff alignment isn’t right. Readjust and try again.

Step 3: Install the I/O shieldMotherboard IO ShieldMichael Krawczyk/Wikimedia
The final step before the motherboard itself, is installing the I/O shield. It’s the silver or black panel that will protect the rear ports of your motherboard and will have come with the motherboard in its box.

Find it and press it into the rear gap in your case. It should be obvious where it goes, but make sure to double check the orientation before pressing it in.

Step 4: Install the motherboardhow to install a motherboard installmotherboard01
At this point you might want to install the CPU first, but it’s not a must. For more information on that, here’s how to install CPU, whether it’s AMD or Intel. To install the motherboard, you’ll want to carefully lower it into the case — coming in at an angle slanted upwards towards the front of the case can help, depending on the chassis.

You want to line up the screw holes on the board with the spacers you’ve put in place. Make sure it also fits neatly into the rear I/O shield too, and that no pieces of metal cover up any of the ports.

how to install a motherboard installmotherboard02
Use the screws included with your motherboard. You may need to hold the motherboard gently in place while you put the first screw or two in, but once those are there, you should have no trouble screwing the rest in. As with the standoffs, if you feel like you’re forcing it, unscrew and start again.

It’s also a good idea to only screw in the screws a little to get them placed, before going around and tightening them all, one by one.

Step 5: The power cablesMotherboard power cables
To give power to your motherboard, you’ll need to plug in its power cables too. For most boards this will mean the 24-pin long connector, and a smaller, four or eight pin connector. The former is usually located on the right side of the motherboard after installing it, while the latter is typically found near the top. Placement can vary, however, so refer to your motherboard manual to be sure.

Route the cables to these locations however you like, then gently push them into the respective slot, making sure they are orientated correctly. If you’re not sure, check the shape of the power sockets as they are rounded and squared deliberately to make incorrect inputs impossible.

With that done, it’s on to the other components in your build. Refer to our guide on how to build a PC for more information on them.