Computer PSU...

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ali68

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Hi all

Left my desktop today to go and do a little shopping, when I came back the comp was off, "must of been a power clitch I thought".

Tried to switch it back on at the front button but alas nothing, checked all the obvious and found nothing. Looking like it may be the PSU is there any checks I can do to confirm this?

Fuse in the PSU is ok.

Happy New Year.
 
on the hard drive power connectors, check voltage between red and black - should be 12VDC, i think. yellow and black should be 5VDC.

The power button will be connected to the motherboard - unplug this and check for continuity when you press the button.

But as the comp turned itself off, i would suggest the PSU.

If you're getting power though (using voltage test above), check for burn marks on the motherboard, something might have burnt out. Test the CPU fan (apply 12V across its wires), see if it was working, the processor might have burnt out.

Lots of possibilities!
 
Continuity on the on/off switch.

No power on the HD leads 12v or 5v.

Cooling fan on the PSU is "lumpy" not put a voltage across that yet but feels a bit suspect.

Are PSU's pretty standard as far as the wiring connections go? This one is rated at 250Watt.
 
You can buy PSU testers that test the status of the Power Good signal under load. I think Maplin do one for about £20.

250W is quite low by todays standards, so your system may be an older type. There are a variety of connectors used on motherboards, so you will need to post the make and model of your machine or a description or picture of the motherboard power connections. It could be an AT type, which is the oldest and has two similar single row connectors, sometimes marked P4 & P5. It is more likely to be an ATX supply with a single connector with two rows. There may be an additional connector with 4 pins in a square.

Depending on the machine (and any upgrades applied), I would go for at least 350W.
 
red & black = 12v logical isn't it, but in a pc that is logical its actually yellow and black that is 12 , red and black is 5v.

back to the question.

have you checked the fuse in the plug, i found that i can blow my fuse by having an accident with the yellow and black.

it may also be the psu has got too warm and turned itself off for some time.

if its still dead then yes 99% of psu's will work, but if your pc is say 5 or 6 years old it may not, since most psu's are soft start, and older psu's were direct start.

by that i mean the psu is turned on by a low voltage on your mobo, to which the pc case on off switch is connected.

older psu's you switched the mains to the psu on /off (yes ok but it was a switch wired in series internaly)

oh, one otherthing (good to remember) if you main mobo power connector is 2 x plugs (some were) the blacks always go in the middle (but most are a one piece plug now)
 
It's an Evesham Vale with athlon700 with a ATX motherboard (K7 pro),
It's getting on in computer years but does fine for surfing etc.

Can't really justify a new machine so soon after xmas (although there is some tempting deals just now :twisted: ) so may try a new PSU.

Plug fuse been checked Breezer, it is soft start and the power plug is a 2 row single piece plug, which would confirm it is an ATX MB as per Igorian's post

Will now go PSU hunting? Any reccomendations for a supplier? dab's, maplin etc.
 
Thanks for that but I'd rather not. Only last night I was looking for a bigger SD mem card and went to E-buyer, good price ,but owing to my location (Scottish islands) they wanted an extra £15 postage :x on top of the existing postage for delivery to me, a little over the top for an item that could go first class post at 30 something pence!!!

Getting a PSU from maplin as I had some discount vouchers to use.


Thanks every one for your help, and a happy new year when it comes.
 
Am I the only one that find Ebuyer's website stuuuppidly slow? It's been loading for over five minutes and still nothing... IF YOU NEED IT, I'd buy one off ebay. A cheap 400 W is probably fine for your computer... but first...

To test your current PSU for fault, unplug it and then try this. Take the motherboard power connector (row of 20 pins - the biggest coming out of your PSU). Short the pin that connects to the green wire with any of the black ones in the same connector (e.g. pins 13 and 14). Now if you plug the PSU in (and make sure the switch at the back is switched on), if your PSU is functional, it will power on.

NOW check the voltages on one of the "HDD power connectors". You wouldn't have measured a voltage on them before because the thing wasn't on!!
 
New PSU fitted and working the old PSU is definately goosed, there is a rather large resistor burnt out, probable cause is the fan seizing.

Thanks everyone for your input.
 
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