Death of a PSU

Features James Hunt Jan 11, 2013

James asks what you can do if your PSU fails - and more importantly, how might you stop it happening at all?

The power supply unit (or PSU) is an essential part of a computer’s operation, but it’s not one we think of very often. Except for hardcore gamer trying to squeeze every watt of power out of their system, the majority of computer users don’t give it a second thought. We simply expect that it’ll supply power whenever we need it too. So when something does go wrong (please excuse the forthcoming pun) it can be something of a shock to the system.

The moment a PSU breaks throws up a number of questions. How could this have happened? Why did it happen? Could you have prevented it? More importantly, with so much power being supplied to such fragile components, it leaves us wondering how much damage has this failure done?

Having suffered through the experience ourselves, our hope is that we can use our experiences to warn you about the dangers of PSU failure, and how to avoid them.

Diagnosing PSU failure

Although PSUs seem like fairly simple boxes, the fact is that the sheer amount of heat they produce, and their reliance on consistent cooling, makes them incredibly prone to failure. All computer components gain slight wear and damage as they heat up and cool down, and the PSU heats up a lot.

Failing PSUs tend to fall into one of a small number of categories. Most frequently, you’ll encounter either an immediate and catastrophic component failure, or a gradual breakdown of efficiency that allows the internals to gradually become inadequate. Spotting a failure requires you to be able to spot strange behaviour and phenomena that might point at a problem with the PSU, so here we’ve tried to cover the most common issues.

When major components in a PSU are failing, there are a few big hints that something’s going wrong. In my case, it was flames shooting out of the back of the PSU air vent, but it’s also possible that you might notice and acrid burning smell of components melting because of an electrical fault, or hear a high-pitched noise called ‘coil whine’, which is caused when electricity makes components physically vibrate (which damages them over time).

Although symptoms of catastrophic failure are hard to miss, if things happen more gradually you might not realise that the PSU is at fault. Symptoms of a failing PSU include inconsistent response to the power button, erratic and apparently unexplained system shutdowns, random resets, and a noisy fan. It doesn’t help that these symptoms can point to completely different problems too, so make sure you diagnose the issue properly if it arises - it could be your PSU, but it might not be! For example, if you’re pressing the power button and the system doesn’t always respond, this may be evidence of a faulty PSU, but it could also be a failing motherboard, or loose connections between components, or even something more basic, such as a deactivated mains supply or master switch.

Assuming that it is properly plugged in and the sockets are switched on, you can then move to diagnose the internals. When you press the power button, a signal travels from the front panel to the motherboard, which then tells the PSU to ‘wake up’. If the signal is disrupted at any point, your power button will become unreliable. A PSU failure is the worst-case scenario here, but also the most common. Unless you have good reason to suspect a problem with your motherboard or power button connectors, the PSU is the most likely area of fault.

Unexplained shutdowns and reboots, by comparison, are reasonably likely to be a software issue. Windows could be automatically rebooting because it’s trying to update, or encountering an otherwise critical system error (i.e. the option ‘automatically restart on system failure’ is enabled). It could even be malware, remotely shutting down your system for some nefarious purpose. To narrow the diagnoses, check your system for malware, disable automatic restart, and temporarily disable updates. If the problems continue, it could be that the PSU isn’t supplying enough power, and Windows is shutting down to prevent data loss or component damage.

If you’ve recently installed new power-hungry components (like a graphics card or processor) then maybe, when their load increases and they need extra juice, your system hasn’t got any more to give, which causes it to shut down. You can test this by removing unnecessary components (such as sound cards, network cards and DVD drives - although a graphics card is the best choice, if your motherboard has onboard graphics) and then booting the system. If the problems stop, there’s a good chance that your PSU is no longer sufficient to power your system. If you haven’t installed anything new recently, the problem might be that your power supply’s efficiency is simply dropping with age. This potentially means that it can no longer supply the power your system needs, and failure is imminent. Either way, you need a new PSU.

Finally, a noisy PSU fan isn’t indication of any fault with the PSU itself, but it does mean that the PSU is in danger of failing. Fans get noisy when they become loose on their bearings, or clogged with dust. A noisy fan is an inefficient fan, and if the PSU isn’t being properly cooled then its components are living on borrowed time. Any permanent change in a fan’s operation is cause for concern, but especially if it’s the fan in your PSU.

Any (or all) of these problems can indicate that a PSU failure is on the cards for your system. A good litmus test is to check your motherboard’s power LED, which should be active even when the PSU is ‘off’ (a low level current keeps it alight to indicate that power is flowing). If it isn’t lit, then either the mains supply is deactivated or unplugged, or the PSU isn’t getting power to the motherboard. It shouldn’t be hard to eliminate the former conditions.

But is there anything you can do to avoid reaching the point of PSU failure in the first place?

Preventing PSU failure

Power supplies might seem like impenetrable little black boxes, but it’s actually quite easy to understand what’s going on: an alternating current goes in, and direct current comes out. Power supplies all have a wattage value, which tells you the rate at which current is supplied. In order to work properly, a PSU has to supply power at a high enough wattage to power all of your components.
The main mitigating factor is how efficient the components inside are - which is to say, how much of the power they supply is lost to heat, rather than electrical energy. As components age, they become less efficient, and less capable of supplying enough power. If you want to prevent a PSU failing, all you have to do is ensure that it stays as cool as possible, which prevents it from becoming worn and inefficient. That’s easier said than done, though - obviously, it’s difficult to cool power supplies directly because they’re heavily shielded and already have their own fans. So what else can you do?

The best way to do this is to make sure your power supply is capable of supplying significantly more wattage than your system actually requires. You can use an online calculator (such as this one) to check how much power your system, with its particular combination of components, needs. A good rule of thumb is to get a power supply with a wattage value 50% higher than the maximum required.

For example, my system requires 270 watts to run, according to the online calculator. The 500 watt PSU I have in it is therefore more than capable of supplying the power my system needs, even as it ages and becomes less efficient. This means the PSU is never running at its full capacity, which should extend its lifespan beyond that of the other components.

You can also further improve your chance of avoiding PSU failures by buying high-quality power supplies. Although they appear to be the same as any other PSU on the outside, cheap and poorly made models can lose as much as 40% of their wattage to heat, which means they’re running closer to capacity and thus more likely to fail. Not all 500 watt PSUs are created equal.

Poorly made PSUs also provide ‘dirty’ power, which means that their output is inconsistent. If it fluctuates too much, it can cause problems with high-performance components (such as overclocked CPUs) that require steady operation, and worse still, could actively damage your system if the power spikes unexpectedly.

To ensure you buy an efficient PSU, you can look for the 80 PLUS efficiency award on the box. It’s a voluntary certification program which guarantees a minimum of 80% efficiency at 20%, 50% and 100% loads. This means they’re less wasteful and live longer; PSUs with this accreditation will run cooler and quieter than similarly powered models with worse efficiency ratings. Some can be so efficient that they don’t even require a fan at their lowest loads, but you’ll pay more for this privilege. The highest rating available is 80 PLUS Platinum, which indicates 90% efficiency on almost every test (they can get away with 89% on the 115v/100% load test).

In general, though, the rules for ensuring your PSU has a long and enjoyable life are the same as any other component in your PC: buy one that’s high quality, keep the load low to minimise its temperature, and make sure there’s good airflow to maximise cooling. Simple enough rules to follow!

Dealing with PSU failure

The fact is that PSUs - regardless of the precautions you take, how much money you spend on them or how well you treat them - will inevitably fail. You have two choices: replace them before they fail, or replace them after. Either way, you risk spending money that could have been avoided, either on a PSU that doesn’t need replacing, or components that might be damaged by PSU failure.

Pre-emptive replacement requires you to pay close attention to your system. If you notice, say, the PSU’s fan running at full speed more frequently than it used to, that’s a safe indicator that the PSU’s temperature is getting higher more often, and that it’s time to replace the hardware. Similarly, if you substantially upgrade the CPU or graphics card, consider replacing the PSU at the same time. These are the most power-hungry components in any system, and a substantial spike in demand has caused many an aging PSU to cross the boundary between ‘just good enough’ and ‘wholly inadequate’.

Most PSUs survive several years under normal use, and some can run for a decade or more. However, there’s no guarantee of how long your power supply is good for, and we recommend that you start thinking about a replacement after five years of continuous use. At the very least, invest in some hardware that can help your test your PSU’s performance, so that you can track how well it’s working.
If you’re sure you have a broken PSU on your hands, there’s only one real option: replacement.

Although it is physically possible to dissemble a PSU, you emphatically should never do this unless you have the qualifications to know what you’re doing. There are no user-serviceable parts inside a PSU, and unless you have specialised equipment to discharge them, they will contain stored electricity. Enough to give you a potentially lethal shock if you touch the wrong piece of hardware - it simply isn’t worth it, even for misers like us.

It’s easier, safer, and much less dangerous to simply replace any faulty PSU. If it’s still under warranty, you should be able to get a replacement from your manufacturer (or system retailer, depending on what’s most appropriate). If you have a spare one lying around, feel free to test it with your system, but even that isn’t a good idea, as old PSU’s will be worn and full of dust and far more likely to fail than a new one. It’s time to break into the piggy bank, we’re afraid!

Ultimately, PSU failure is something that you should be aware of in all systems, but particularly those that are more than three or four years old. It doesn’t take much effort to look after your power supply, but the potential benefits of doing so more than outweigh the time you lose.

My PSU Exploded! Now what?

If your PSU does fail before you can replace it, you obviously have to buy a new one, but you’ll also have to check that your system wasn’t sufficiently damaged. Depowering components in the middle of operation is a bad idea for a variety of reasons, so once you’ve installed a fresh power supply and got your system running again, there’s what you need to check.

1. Was the hard drive damaged?

If a hard drive loses power mid-write, it can damage the disk platter, causing data loss and access problems. When power is restored, run a full surface scan of your hard drive to find bad sectors. It’ll take ages, but it’s the only way to be sure, and a better way of finding out than waiting until your important photos/essay/presentation becomes corrupted and irretrievable.

2. How’s the motherboard?

Since motherboards are directly connected to the PSU, they often bear the brunt of power surges and PSU faults. When you remove the damaged PSU, check for things like scorch marks that may indicate problems with the motherboard. If it still works when you plug a new PSU in, then you’ve probably escaped without any major damage, but it’s worth checking the BIOS for temperature & voltage numbers, and manually testing the motherboard’s ports and functions just to be sure (you can buy a motherboard tester if you want to be more thorough).

3. Were the CPU & RAM affected?

Processors and RAM modules are full of fragile transistors that can be easily toasted by a power supply fault. Again, check them for physical signs of damage when you take the broken PSU out, and run benchmark software and analysis software to check for performance problems. If the tests complete fine, your components are probably safe, but treat any crashes or particularly poor scores with suspicion!

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