The power supply on one of my computers doesn't seem to be working, although I'm worried it might be the motherboard again.

It smelt of burning whilst I was operating it, so I quickly went to shut down, but before I did, it powered itself off. I opened it up immediately and the inside was extremely hot. After an hour or so, I plugged it back in.

None of the fans in the power supply worked. The fan on the motherboard itself gave one turn and stopped, followed by a constant orange light on the motherboard. I don't know about the front-panel lights since they haven't been re-connected since I had the computer repaired a year ago. None of the components look "bulging" or discoloured. There isn't an awful lot of dust present, although I guess it could do with a clean. I've had motherboard failure in the past, but at least then the power supply started.

All is under surge protection. The PSU is a 400W and the motherboard I think is an AGP/ 8X.

take a screwdriver or something to the 20/4 pin motherboard plug on the PSU and short the green to black and see if the power supply kicks on

The motherboard shorts out the Power On which your motherboard normally does when you press the momentary power switch on the front of the case. By shorting out the Green wire to any Black wire it bypasses the motherboard allowing you to determine if the problem is the PSU or not.

What smurfgod didn't cover is that for safety reasons you should turn off the PSU by the switch on the rear of it, or unplug it if there isn't a switch. When you disconnect the 20/4 pin connector from the motherboard be careful that when you jump out the Power On that you aren't creating a potential short. For this reason I suggest using a insulated wire for the jumper.

If you have a voltage meter you can read the different rail voltages while you have this set up. Put the black probe of the voltage meter in any black wire socket of the 20/4 connector and use the pinout at this site to check the voltages.

Once you have installed the jumper and check to be sure that there are no potential shorts you are ready to power up the PSU.

Well I've found out that the PSU is knackered by putting it into another machine. I think the heatsink has had it too. Either that or it needs a good clean.

Worth a look: CPU fans and PS

Don't forget the thermal compound.

Louis

Am I not right, however, that whether the heat sink is working or not does not affect the processor working?

So even if the heat sink is knackered, shouldn't the processor still operate? Which only leaves me to conclude that the processor has been fried? (I can't get it off at the moment since I don't have a wrist ground nor the tube-stuff [the name has escaped me] that you put between the CPU and the heat sink)

(assuming the PSU is operational)

The machine now goes "click" "click" "click" when booted up with a working PSU.

Without a heatsink the CPU will either shut off to save it self from frying or it will quickly overheat and destroy it self. The word you were searching for is thermal compound. You don't need a grounding strap to work on a computer just make sure to touch the case before you touch any of the components.

Mm I was thinking it could shut itself off, but then again, I didn't think AMD processors did that. Its an Athlon XP I think.

I'll have a look tomorrow. The fan on the heat sink DOES spin but actually at quite a medium speed (I can't remember how fast it went in the first place!). I cleaned out the dust too but I doubt it had much influence.