Power Supply Unit

If your PC or laptop has been behaving erratically, it might be your PC's PSU. This handy tip from PC Advisor reader Andy Scott explains how to check your PC's power supply, and find out what's wrong with your PC.

"If your PC sometimes works fine, but intermittently displays the 'Blue Screen of Death' (BSoD), it's worth checking the PC's power supply unit (PSU). Some low-cost PCs come with cheap PSUs that can just about support the installed hardware. If you upgrade your equipment with an extra hard disk drive, a better graphics card, a new
DVD drive or more memory than the PSU can handle, it may start to fail.

"Dust build-up can also reduce the life of the PSU. Symptoms are usually intermittent, and include unexpected reboots, startup failures, USB device failures, and hard-disk or memory errors. These issues often mysteriously fix themselves, only to return later.

"These errors can be more frequent when you're doing something that requires more power than is normal, and they will usually become progressively worse until the PC eventually fails to boot altogether.

"The solution is simple: replace the PSU with one that can cope with the power requirements of your installed components. If the case is reasonably well-designed then you can simply take out the old PSU and slide in a new one, although it can be tricky if there isn't much room inside the case. Make sure your new PSU has enough connectors for all your hardware."

Problems with PC power supply: how to fix them

Thanks for the tip, Andy. We've traced all sorts of strange problems down to faulty PSUs, and it's a component that's all too easy to overlook when diagnosing problems. For example, one particular motherboard we were testing refused to boot unless a graphics card was plugged in, even when using its integrated graphics. Replacing the PSU fixed this problem.

A decent PSU can also go some way to silence your computer, thanks to higher-quality and quieter fans.

Graphics card upgrades can be one of the biggest causes of PSU problems as they can draw a large amount of power. Be sure to research online to find out your card's requirements before installation.

Sometimes software tools can help you to diagnose a problem with your PSU. These are often bundled along with your motherboard or available as a free download from the motherboard vendor.

Asus, for example, provides a tool that reports the voltages being supplied to the motherboard. There should be at least +12V, +5V and +3.3V inputs, along with their actual measured voltages. If any of these values strays too far from its intended value, you probably have a PSU issue. For example, if your +5V line is measured at only +4.5V, your PSU isn't delivering power as it should.

Be warned that replacing a PSU is rarely as simple as sliding in a new one. There will be many cables to disconnect – at least one to each system component and probably two to the motherboard. Some, or all, could also be clipped into place with cable ties. Each component will, of course, have to be reconnected to the new PSU.

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