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Desktop help please
Ninehigh - 10/5/12 at 06:50 AM

Morning all.

Shortly after I woke up my gf said "could you take a look at the computer, it's not switching on"

And it's not... Nothing at all.

I've cleared the dust out, changed the fuse in the power lead and checked for loose cables.

My tools are a bunch of screwdrivers and this laptop, is there anything else I can diagnose before I start randomly replacing parts?

Btw if the psu is ok (we replaced it last year) but the motherboard is jiggered it would switch on, right? The only other thing I can think of is the power switch itself, but it was on when I left it last night..

ReMan - 10/5/12 at 07:12 AM

"Btw if the psu is ok (we replaced it last year) but the motherboard is jiggered it would switch on, right?"

Wrong
Some of the switchyonness is controlled through the motherboard.
Some older psu have a reset button on them?
Else get you multimeter out...
I think that the "ON" signal would be dircect to front panel switch
http://www.helpwithpcs.com/courses/power-supply-basics-inc-pinouts.htm

[Edited on 10/5/12 by ReMan]

Ninehigh - 10/5/12 at 07:21 AM

This is it it's not an old psu.. but the chassis, mb etc is nigh on ten years old.

The psu vents were caked in dust, could it just burn out?

britishtrident - 10/5/12 at 07:59 AM

Replacement power supplies are of variable quality ie some are crap. As a rull of thumb if the fan starts for a second or so when you press the on button from cold start them the problem is a short somewhere or an internal lead disconnected rather than the power supply.

The power supply is protected by automatic thermal fuses which trip if an overload is present they automatically reset if they are allowed a minute or so to cool down (ie with power off).

First step with problems like this is usually to turn the case upside down and give it a good shake, this will reveal anything loose inside the case (eg screws and washers) causing a short.

Second step is disconnect everything that is plugged into the PC including the keyboard, mouse and all USB devices and try again.

Third step is try a different power lead as it is very common for Euro sockets to suffer from arcing connections.

Fourth step is open the case an look for any leads that have become disconnected from the motherboard or leads that have been trapped by the case or sawn through by the fan

Fifth step is disconnect all the drive cables and try again.

If no joy replace the power pack.

[Edited on 10/5/12 by britishtrident]

Ninehigh - 10/5/12 at 08:06 AM

Looks like a psu replacement then

Good job it wasn't a majorly expensive one!

Thankyou

dhutch - 10/5/12 at 08:18 AM

quote:
Originally posted by Ninehigh
Looks like a psu replacement then

Good job it wasn't a majorly expensive one!

Thankyou

You can test the PSU to a certain extent in isolation by jumping the green 'power on' lead to a black 'ground' lead.


http://www.google.co.uk/search?hl=en&pq=psu+green+lead+jumper&cp=12&gs_id=n&xhr=t&q=psu+power+on+without+motherboard&safe=acti ve&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=999&bih=488&wrapid=tljp1336637795388014&um=1&ie=UTF-8&tbm=isch&source=og& ;sa=N&tab=wi&ei=c3mrT819yODyA7KUyecE


Daniel

balidey - 10/5/12 at 09:07 AM

I've known several switches fail.
The front switch just sends a trigger to the motherboard.
If you can find details of the board online you may be able to figure out which pins to short out. This gives the MB a temporary pulse which starts it up.
Or if you don't feel confident doing this you could do the short at the switch end.
EDIT: Looks like thats what dhutch posted about above.

[Edited on 10/5/12 by balidey]

rf900rush - 10/5/12 at 10:54 AM

Had My PC died last year
Look like dead PSU

Was the Graphics card in the end.
The fan on the graphics card had stopped.

You can disconnect most items jsut leaving the M/B to see if it powers up. Lights on fan running to see if the PSU comes on.

Then if still dead the justs leaves CPU , M/B and PSU to swap out.

MikeFellows - 10/5/12 at 11:34 AM

unplug the psu for a few mins to discharge any power

then in a quiet place plug the psu in, while having your ear close to the psu, you will hear a faint crack as it powers up the 12v rails - 95% of the time this means the psu is working - admiteddly not always. no crack and the psu is definatley dead

Ninehigh - 15/5/12 at 08:27 AM

Damn it all to hell!

Replaced the psu and it started up fine, but no picture... Hmm no doubt I've touched it as I've jiggled everything about or it's blown in some other way.. No worries I shall look for a new one of them too..

It's arrived this morning, put it in, started up and still no picture!
What's more is there's no lights on the keyboard and mouse.. The usb slots have gone too!

Looks like it's new board time too... And I'm going to have to do this one on the sly cos she's already said she's not spending any more money on it... Grrr....