How to Diagnose Desktop Computer Power Supply Failures

Your desktop won't turn on. No lights, no fans, nothing. Before assuming the worst, the power supply unit (PSU) might be the culprit. It's one of the most common failure points, and diagnosing it doesn't require technical expertise.

At SnapFix Repairs in Oldham, we see PSU failures weekly. Here's how to identify them and what to do next.

What Does a Power Supply Do?

The PSU converts mains electricity (240V AC in the UK) into the various DC voltages your computer components need. Motherboards, processors, graphics cards, and drives all require different voltages.

Modern power supplies are sophisticated devices with safety features, efficiency ratings, and smart power management. When they fail, your computer simply won't work.

Common Power Supply Failure Symptoms

Complete Dead System

The most obvious sign is a computer that shows no life whatsoever. Press the power button and nothing happens. No LED lights on the case, no fan spin, no beeps, nothing.

This suggests the PSU isn't providing any power, though it could also indicate a motherboard issue.

Intermittent Power

The computer starts sometimes but not others. It might power on after several attempts or work fine for days then refuse to start. This inconsistency often points to a failing PSU.

Components inside the PSU degrade over time, causing intermittent failures before complete death.

Random Shutdowns

Your computer turns off unexpectedly during use, especially under load. Gaming, video editing, or running multiple programs triggers shutdowns. This suggests the PSU can't deliver sufficient power when demand increases.

The system might restart immediately or require several minutes before powering on again.

Strange Noises

Grinding, buzzing, or whining sounds from the PSU area indicate failing components. The PSU fan bearing might be worn, or internal components are failing.

Electrical buzzing or crackling sounds are serious warning signs requiring immediate attention.

Burning Smell

Any burning smell from your computer demands immediate shutdown. Unplug it and don't restart. This indicates serious electrical failure, potentially fire risk.

PSU capacitors can fail dramatically, releasing smoke and odor.

Basic Diagnostic Steps

Safety First

Unplug the computer from the wall before opening the case. Press the power button a few times after unplugging to discharge any remaining electricity. Never open the PSU itself - they contain dangerous capacitors that hold lethal charges even when unplugged.

Check the Obvious

Verify the wall socket works by plugging in another device. Check if the PSU power switch (usually on the back) is turned on. Ensure the power cable is fully seated at both ends.

Look for a small voltage switch on the PSU (usually red) - it should be set to 230V in the UK, not 115V.

Visual Inspection

Open your computer case and look at the PSU. Check for bulging or leaking capacitors - they look like small cylinders and should have flat tops. Bulging tops indicate failure.

Look for burn marks, discoloration, or any signs of overheating on the PSU casing or nearby components.

The Paperclip Test

This tests if the PSU works independently of other components. You'll need a paperclip and caution.

Unplug the PSU from the wall and all computer components. Find the largest connector (24-pin motherboard connector). Unbend the paperclip into a U shape. Locate the green wire terminal and any black wire terminal on the 24-pin connector.

Insert the paperclip to bridge these two terminals. Plug the PSU into the wall and switch it on. If the PSU fan spins, the PSU has basic functionality. If nothing happens, the PSU is likely dead.

This test only confirms the PSU can start - it doesn't verify it provides correct voltages under load.

What Causes Power Supply Failure?

Age and Use

PSUs typically last 5-7 years with normal use. Components degrade naturally. Capacitors dry out, affecting voltage regulation and stability.

Heavy users or systems running 24/7 experience faster wear.

Power Surges

Lightning strikes, grid fluctuations, and electrical issues damage PSUs. Even with surge protectors, severe events overwhelm protection circuits.

The PSU often sacrifices itself to protect more expensive components like the motherboard and processor.

Overheating

Dust accumulation blocks airflow, causing the PSU to overheat. High ambient temperatures in poorly ventilated cases accelerate failure.

PSU fans fail over time, eliminating cooling and causing rapid degradation.

Cheap Quality

Budget PSUs from unknown manufacturers use inferior components. They fail prematurely and may damage other computer parts when they do.

Name-brand PSUs from Corsair, EVGA, Seasonic, or Be Quiet cost more but last longer and fail more safely.

Overloading

Adding components without checking PSU capacity causes problems. A 400W PSU powering a system that needs 500W operates constantly at maximum capacity, reducing lifespan dramatically.

When to Repair vs Replace

Always Replace, Never Repair

Unlike other computer components, PSUs should never be repaired by anyone except specialized electronics technicians. The risks outweigh any savings.

Even professionals typically replace rather than repair failed PSUs. Replacement units are affordable, and repairs are time-consuming and potentially dangerous.

Choosing a Replacement

Calculate your system's power requirements before buying. Online PSU calculators help determine the right wattage. Add 20% headroom for efficiency and future upgrades.

Check the efficiency rating - 80 Plus Bronze minimum, Gold or Platinum for better efficiency and lower electricity costs. Ensure the PSU has the correct connectors for your components.

Modular or semi-modular PSUs offer better cable management but cost slightly more. Non-modular works fine for budget builds.

What It Costs in Oldham

Basic replacement PSUs start around £40-£60 for quality 500-600W units. Mid-range options cost £70-£100 with better efficiency and features. High-wattage or premium units run £100-£200.

Installation is straightforward for experienced technicians. At SnapFix Repairs, we stock common PSU sizes and can typically complete replacements the same day.

Total cost including parts and labor usually ranges £80-£150 depending on PSU choice.

Preventing Future Failures

Use a quality surge protector - not just a multi-plug extension. Clean dust from your computer every six months, paying attention to PSU vents.

Ensure adequate case ventilation. Don't overload your PSU by adding power-hungry components without checking capacity.

Buy quality power supplies from reputable brands. The extra £20-£30 saves money and frustration long-term.

When to Call SnapFix Repairs

If your desktop shows PSU failure symptoms but you're not confident diagnosing yourself, bring it to our Oldham workshop. We test thoroughly to confirm the PSU is the problem before recommending replacement.

Sometimes what appears to be PSU failure is actually a motherboard or other component issue. Professional diagnosis prevents buying unnecessary parts.

We keep quality replacement PSUs in stock and can get your computer running the same day in most cases.

Contact SnapFixRepairs in Oldham for reliable power supply diagnosis and replacement.