Help !!! Is it my power supply? or something else?

  teddyman5 17:52 19 Jan 07

have a problem with my computer ( I'm using my daughters at present - only while she's at school ) in that there is no power.It was like that this morning so I checked everything and found the fuse gone in the plug.All other things OK, surge protector not tripped etc.So I changed the fuse, plugged in and there was a loud pop with a faint smell.I would suspect the power supply may have blown but I don't really know.So - any advice on what to do next, what and how to check?
The supply is a Switching Power KY-500 ATX P4 400W whatever all that means.Any help would be very greatfully received - thanks in advance.

  Diemmess 18:02 19 Jan 07

You don't have any alternative to replacing with a new PSU.

If you happen to have an old spare PSU you could try that first!

In my opinion the fault lies in your present PSU because the plug's cartridge fuse blows so quickly.

If there were a dead short somwhere on the mobo or peripherals it would overload the low voltage line from the PSU, maybe even kill the PSU, but not draw enough current at mains voltage to blow the plugtop fuse.

  Blitzer 18:04 19 Jan 07

If the PSU in your PC is the same as that in your daughter's, e.g. wattage is the same or very close, you could try her's in your PC to confirmt your PSU is at fault. I did however experience the same with my other PC and it was the PSU that had died, I assumed some internal short causing it to blow the fuse as soon as it was connected to the mains. HTH

  teddyman5 18:05 19 Jan 07

Is there a way to check - say withy a multimeter? but which terminals to use?
Also If I have a prob will same happen again with new psu?

  teddyman5 18:07 19 Jan 07

My daughters was a Xmas pressie so I'm not going to mess with that - more than my life's worth!

  Fruit Bat /\0/\ 18:14 19 Jan 07

click here
click here

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

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.

2. Power supply calculator click here

Guide to changing PSU
click here
click here

  Diemmess 18:19 19 Jan 07

...don't even try to explore the psu's innards!

A straight check with a multimeter is not going to work, unless it has some load on it. The circuitry is much too subtle to make that a runner.
Don't waste your time.

One last check you could try, is to disconnect all the power cables to HD/s CDRX's Floppy Drive and USB devices, leaving the mobo with nothing to do except power itself.
If you feed your monitor power via the PC, disconnect that also.

Now if another fuse doesn't blow then it must be one of the things you have just disconnected.
If the fuse blows again you really must replace with a compatable new PSU.

  teddyman5 19:19 19 Jan 07

New fuse doesn't blow - nothing happens.

  Diemmess 20:47 19 Jan 07

I still think the fault lies in the PSU, but try reconnecting the monitor and switch on again without even the HD connected.
The computer - if the PSU is sound will go through the early boot routine and stop with an error message just before Windows would nomally load.

I hope (for your sake in the long term) almost nothing will happen and the monitor will say No Signal.

  Diemmess 22:23 19 Jan 07

Expressing only my opinion with these posts:
the balance of probability is that something went badly wrong with the PSU.

The result was the various things that have happened since.

A PSU is one of the most likely components to fail after say a CD reader/writer.

Fortunately it is one of the cheaper components and easy to replace.

If you are lucky then that is all that is wrong. However, failure of the PSU can occasionally damage or destroy all sorts of other things in the computer. Unlikely but still a possibility.

Gadgets for testing a PSU do exist but good ones can cost more than a replacement PSU.

Please let us all know how your problem is resolved?

  woodchip 22:26 19 Jan 07


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