Fuse keeps blowing - any suggestions?

[itz_baseline]

Something wierd keeps on happening to my PC and I've never come across anyone with the same problem. Basically the fuse keeps on blowing in the plug on the power cable on the PC. It's plugged into a 4-way adaptor and non of the other things plugged in )speakers, printer etc) blow their fuses so I've ruled out a power serge form the mains.

The strange thing is I can leave the PC on for days solid as long as I don't do much with it (i can manage some general internet browsing and msn) but as soon as I try and do anything that uses a large amount of cpu the fuse blows (for example if I try and sync my iPod or use a more complex bit of software like Google Earth).

At first I thought it was the power unit so I replaced the whole PC power unit for a 400w unit and the same thing happens. A normal power cable uses a 5amp fuse which it blows, so I tried replacing it with a 13amp fuse which also ends up blowing.

Anyone seen this before and got any suggestions? I really can't think what else it could be and wondered if anyone had any ideas before I try buying a new motherboard and CPU (obviously I want to avoid if possible).

Thanks in advance
Basey

>> Edited by itz_baseline on Friday 13th January 18:50

[GreenV8S]

Seems like there's a short somewhere within an internal circuit which is only powered occasionally. Are there any other components (fan, perhaps?) within the PC which are powered directly off the mains?

[Trooper2]

Sounds like a short to ground (earth), check for a pinched wire(s).
I would think that the problem would have to lie between the power supply for the PC and the wall socket that it's plugged into as once you get passed the power supply the amount of amperage and volts drops way down.

[mattley]

Usually, if the fault's inside the unit the PSU will shut down way before the fuse gives out, but though worth checking I'd be looking the other side of the PSU.

Given that it looks power related and you've changed the PSU whats the rating of the fuse? Typically a 400W PSU shouldn't pull more than about 1.5 Amps, but a good one with big smoothing caps can pull way more as the load ramps, so even a 5A fuse may not be enough.

It's also worth checking the power block and the lead especially the fuse terminals for dust or excess oxidisation. If they're looking a bit dull, get a bit of abrasive on 'em and see how it goes.

[GreenV8S]

Have you been using the same power lead the whole time?

[kneedowndeano]

sounds like the PSU is on it's way out. I had this happen to a client of mine. After swapping out the PSU everything was fine from then on.

[itz_baseline]

kneedowndeano said:

sounds like the PSU is on it's way out. I had this happen to a client of mine. After swapping out the PSU everything was fine from then on.

I've already changed the PSU as I mentioned below, the problem still exists.

GreenV8S said:

Have you been using the same power lead the whole time?

Nope, I've used 4 different power leads in total (as I had some lying around and it was easier to just change power lead as I ran out of fuses at one point)....problem still occured with all 4 power leads.

mattley said:

...whats the rating of the fuse?.... If they're looking a bit dull, get a bit of abrasive on 'em and see how it goes.

Fuses used were both 5amp and also 13amp as mentioned below, so as you say if should only be pulling 1.5amps....so there's no way a 13amp fuse should be blowing.

GreenV8S said:

Are there any other components (fan, perhaps?) within the PC which are powered directly off the mains?

Yeah there's 2 fans within the PC (one fan against the CPU, and one on the case itself cooling the whole contents of the case but these both run from the PSU....there's also 2 fans in the PSU itself, but thats a standard thing. I have got a couple of LED's that light up the clear case blue but there's nothing out of the ordinary with my set-up, and I've been running it for 2 years without any problems at all and suddenly the problem has started.

I've had a look at all cabling and nothing seems to be pinched or causing an obvious short...I'm just baffled.

Thanks for the initial suggests, any more would be helpful

Cheers
Basey

[GreenV8S]

itz_baseline said:

Yeah there's 2 fans within the PC (one fan against the CPU, and one on the case itself cooling the whole contents of the case but these both run from the PSU....there's also 2 fans in the PSU itself, but thats a standard thing. I have got a couple of LED's that light up the clear case blue but there's nothing out of the ordinary with my set-up, and I've been running it for 2 years without any problems at all and suddenly the problem has started.

In my experience, fans are normally driven off the 12v supply from the PSU rather than directly off the 240V AC. You are looking for anything connected directly to the 240AC.

[mattley]

itz_baseline said:

.so there's no way a 13amp fuse should be blowing.

Woah. .........

If it's blowing 13amp fuses i'd be worried about why my main fusebox or breakers hadn't trippped out first. PCs do not take out 13A fuses without smelling bad, you may have some electrics in your house gone a bit wrong.

[itz_baseline]

mattley said:

itz_baseline said: .so there's no way a 13amp fuse should be blowing. Woah. ......... If it's blowing 13amp fuses i'd be worried about why my main fusebox or breakers hadn't trippped out first. PCs do not take out 13A fuses without smelling bad, you may have some electrics in your house gone a bit wrong.

Good point - my uncles an electrician, I'll get him to bob round and take a look. It's strange that it's only my PC though and non of the other electrical items in my house though.

[GreenV8S]

mattley said:

If it's blowing 13amp fuses i'd be worried about why my main fusebox or breakers hadn't trippped out first.

The main fusebox and breakers etc should be rated at far more than 13A. There is no way that faulty equipment should be able to trip the main breaker, the plug fuse should blow way before then. The blown fuse suggests that the fault is somewhere within the PC or mains lead. I'm struggling to think where though.

Some PCs have a 'daisy chain' mains outlet which can be used to power the monitor off the base unit. Does yours have anything like this? Also might be worth trying the PC in a different wall point in case it's something daft like the extension lead crossing earth/neutral or something.