Loud bang on pc

  julas64 11:22 05 Dec 2010

Early hours of this morning there was a loud bang and my electric was tripped. At the time there was a smell of burning coming from the back of my sons pc around the area of the fan, the PC was actually powered off but the plug was still in and switched on. Because of the smell and fear of doing further damage im too frightened to plug it in again to see if it will actually switch on. Does anyone have any idea whether it could be the fan that has blown or is it more likely to be something more sinister and expensive. I would be grateful for any help or advice.

  Fruit Bat /\0/\ 11:28 05 Dec 2010

It sounds like the PSU (Power supply Unit) has blown.

How expensive depends on if it has taken other components with it like the motherboard CPU and hard drives (usually they don't).
Usually they just stop rather than go with a bang.

A new PSU is not expensive and reasonably easy to fit.

If renewing a PSU check:

1. The physical size of your PSU, some are hard to replace due to being a non standard size.
2. The amount of power need from the PSU don't skimp.
3 The correct connections for your equipment

1. Physical Dimensions

Besides the specs and form factors, the physical dimensions are also important factors in selecting a compatible power supply. Here is an outline of the physical dimensions of most standard power supplies:

# ATX: 6x3.5x5.5", HxWxD. Most common. Uses 4 mounting screws.
# Mini-ATX: 5x3.5x5", HxWxD. Rare size. Uses 4 mounting screws. Can be used in a regular ATX case, but often not the other way around.
# MicroATX: 5x3x4", HxWxD. Use 3 mounting screws. Not interchangeable with ATX or miniATX.
# Flex ATX: Even smaller than Micro ATX. Various sizes according to case specs; often not interchangeable.

Use the data above to determine if a particular power supply would fit your case.

The quality of a power supply can be estimated by its weight. While this is not a true scientific or thorough measurement of the power supply reliability, it is nevertheless a very simple and easy way for ordinary PC users to estimate and compare the quality of a power supply. Why weight matters click here

2. Power supply calculator click here

3. Correct connections
Some boards have 20 pin connectors others 24 pin
There is often a 4 pin plug required to power Intel CPUs
Molex D plugs for IDE HDD and CD/DVD drives
SATA power connections for latest HDDs and DVD drives.

Guide to changing PSU
click here
click here

  spuds 11:42 05 Dec 2010

The possible problem and remedy seems to have been covered in Fruit Bat's response.

To perhaps add to the above, go for a bigger wattage/amp psu if necessary. The price difference is usually nominal. Anything 400w or less go for bigger.

If you do remove the casing, then have a look at any other signs around all the other components for possible 'shorts' etc. If you are not sure, then get someone who is familiar with electrical items, and make sure that the plug is taken out of the wall socket first (check that as well, fuse, wires etc).

  Terry Brown 11:56 05 Dec 2010

I would say as a first step,remove the harddrive (to protect your data)and if possible connect it to another computer as a slave (you may need a caddy (about £6 from Amazon).

Unplug all USB drives,printer, scanner, modem and any thing else that is connected externally(including the monitor)

Check the fuse in the plug- replace with a 3amp if necessary.

Plug in, to see if you any response,try switching on.
if you get a response (lights or beeps) turn off and re-connect the Monitor.

As there is no harddrive connected, if the motherboard,power supply and CPU (processor) are ok, you should get a bios boot up to the screen (text only).

If there is no response, you will need to remove the power supply and test it, for this you will need a Multimeter. or someone with access to one. this link will give you an idea of what is involved click here if unsure DO NOT ATTEMPT YOURSELF as it can be very hazardous to your health. You may be better off taking it to a local electrical shop for checking.

You could try connecting a PSU from another computer to your system and trying it, but only if you are sure of what you are doing.

If the PSU is ok,but the problem persists, then the problem could be either the motherboard or the CPU, and you may be better off getting a new base unit or a new computer (Christmas is coming)


  skeletal 15:54 05 Dec 2010

I agree with the replies so far. However, one further step (a step too far perhaps?) is that from your description, I would hazard a guess that the components that have failed in the power supply are related to EMC (ElectroMagnetic Compatibility). These can be wired directly across the mains and are under a lot of electrical stress. Their failure can be spectacular, but the good news is that, unless hot bits of plastic/metal etc have physically damaged parts of your computer (unlikely), everything should be fine following a power supply repair.

If it is these components, a repair can actually be made to the power supply itself if you know what you are doing. Unfortunately, in this modern world, although the components are fairly cheap (a pound or two) the labour cost of such a repair is likely to be greater than just buying a new power supply.

A slightly related story: my son’s car’s gearbox developed a fault. The main dealer failed to mend it and could only offer to change the box for about £5000. Some internet searching and help from a car forum member had us change a £2 spring which completely cured the fault!

Luckily, new power supplies are a bit cheaper than £5k...


  julas64 12:12 07 Dec 2010

Thanks guys. I took it to my local Pc Maintenance shop and they fixed it. Luckily it was only the psu and there was no other damage, thank god! They did tell me this was probably due to the fact i had the pc connected to a surge protector. Im a bit confused tho as when i asked how it could have happened as it wasnt switched on, they told me it couldnt have been the computer which blew then, it must have been another appliance which caused it. Although ive had no problems with anything else in the house, and how come nothing else was affected by it. Does anyone have any idea bout this, im now worried that it could happen again.

  spuds 12:21 07 Dec 2010

Surge protector?.

I use these for 'spikes' in the electricity, I cannot see how they would 'destroy' a psu.

Do you have surge protection or trip-out devices installed in your electrics system, from mains to individual items?.

  lotvic 12:26 07 Dec 2010

""the PC was actually powered off but the plug was still in and switched on.""

There was power going to the PSU although it wasn't 'running'
(If I switch my pc off there is still a light on the motherboard unless I switch off at the mains plug)

  uk-wizard 17:33 07 Dec 2010

Most PCs leave the power supply on at all times (or they put a mains switch by the mains input socket at the back where you cant get at it except by memory -HP are you listening?).

  skeletal 19:56 07 Dec 2010

Unless something else is going on that we don’t know about, like your “surge protector” is actually a petrol standby generator or an alien space-craft, a surge protector cannot damage a PC, or indeed anything else. In fact its job is to “protect” equipment (the clue is in the name!).

However, they can themselves be destroyed if a big surge appears; i.e. as they do their job of protecting, they get destroyed, a bit like a fuse. Unlike a fuse, which you can easy tell has blown, you may never know a surge protector has “gone” unless you hear a bang and can see physical damage (you can’t always).

The PSU itself will have similar components to a surge protector, those to which I referred as “EMC”. Depending on design, they may be wired so that they are permanently connected across the mains, even if you think you have turned the computer off. They can blow, with or without a surge occurring.

Obviously the repair men have sorted you out and as per my earlier post, the PSU problem was one that did not lead to other damage.

It would have been good to know the exact cause, but I assume they just replaced the entire PSU rather than locate the failed component.

Glad you are sorted.


  julas64 13:20 08 Dec 2010

Thanks everyone.

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