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Tony
19-05-2013, 11:22 AM
It looks like the PSU on my main PC has died. I press the on button and nothing happens - no fans, nothing. There is an LED lit on the mobo, but nothing else. It could be the switch I guess, but I'm suspecting the PSU.

So I'm looking for recommendations for a replacement. The dead one is a Q Technologies 560w ATX, and I'd be looking for a similar spec - good make, quiet, 600-ish watts. One with modular cables that you can plug in would be good, but not vital.

Any suggestions?

Tony
19-05-2013, 11:45 AM
What about these (http://quietpc.co.nz/zmx00-gt) ones?

Agent_24
19-05-2013, 01:48 PM
If the motherboard has an LED going then the PSU is at least working up to the point of providing the 5v Standby rail.

It could well be the motherboard, button or PSU that's faulty - or even some other part.

Those Zalman PSUs look OK on paper, but I don't know what the quality is like. They are entry-level models so I wouldn't expect them to be awesome in terms of longevity.

dugimodo
19-05-2013, 04:19 PM
It can be risky but if you have a steady hand on the 24 pin plug from the psu to the motherboard you can use a piece of wire to short the green wire to one of the black ones, this should power up the PSU and helps prove where the fault is.

Always safest of course if possible to test by swapping with known good parts rather than do this sort of thing.

Tony
19-05-2013, 04:23 PM
OK, thanks for that. So it might be a good idea to get it checked out before I fork out for a PSU? If the mobo was stuffed, I would have thought that at least the fans might have powered up, even if they immediately died - or is that not true? Is there anything I can do with limited hardware knowledge or diagnostic gear to narrow the possibilities? I do have another PC with an ATX PSU, but I don't want to dismantle 2 PCs if I can avoid it.

Tony
19-05-2013, 04:25 PM
It can be risky but if you have a steady hand on the 24 pin plug from the psu to the motherboard you can use a piece of wire to short the green wire to one of the black ones, this should power up the PSU and helps prove where the fault is.That idea does make me a little nervous - I have visions of a flash of light and a puff of smoke and a totally fried machine :(

Agent_24
19-05-2013, 04:41 PM
Is there anything I can do with limited hardware knowledge or diagnostic gear to narrow the possibilities? I do have another PC with an ATX PSU, but I don't want to dismantle 2 PCs if I can avoid it.

If you have a known working PSU then swapping them would be a good start.

Alternatively you could try the manual power on method as dugimodo suggested, although I would first try doing this with the PSU completely disconnected from all other hardware. If the PSU is faulty, and you force it to power up, it could ruin something.

Tony
19-05-2013, 05:23 PM
So if I do try the mission impossible approach (green wire! black wire! - which?) then what would I expect to happen if the PSU is working, and what if it is faulty?

Agent_24
19-05-2013, 05:40 PM
Short the green wire (PS_ON) to any of the black (GND) ones (ie: pull it low)
If it's working OK it should turn on; the fan will start spinning, any lights will come on. You can verify the voltages are sensible if you have a multimeter etc.

If it is faulty, it may not power on at all, or power on and then turn off quickly (note: this can also happen if it has no load), or power on with incorrect voltages, or blow up (unlikely, if that didn't already happen).

If the thing does appear to start OK, you could try again with it actually hooked up to the motherboard.


You might also like to try swapping the power button with the reset button in case the power button has broken and nothing else is wrong.
(Or just shorting out the power button pins with a screwdriver or such, but just using the other button is safer, so you don't miss)

Tony
19-05-2013, 05:55 PM
OK, thanks. I think I'll try swapping the start and reset switches initially. If it still doesn't work, I would think it is much more likely to be the PSU rather than the mobo? I don't have any test equipment (I'm not a hardware/electrical person at that level), I'll bite the bullet and swap out the PSU for the one from my other PC and see what happens.

Tony
19-05-2013, 06:19 PM
Swapping power and reset made no difference. If I swap PSUs, what is the minimum I have to connect to establish whether it is working or not? Is the 24-pin on the mobo enough, or is there more?

Tony
19-05-2013, 06:38 PM
OK. It looks like the PSU. I connected just the 24-pin connector, and when I connected the suspect one to the known OK machine, it was dead. When I connected the known good PSU to the dead machine, it powered up the fans on the mobo.

That would seem pretty conclusive, I would think?

Agent_24
19-05-2013, 07:11 PM
Swapping power and reset made no difference. If I swap PSUs, what is the minimum I have to connect to establish whether it is working or not? Is the 24-pin on the mobo enough, or is there more?

The main 20 or 24 pin connector and any auxiliary power connectors (Near the CPU is usually an extra 4 or 8 pin connector)
Some boards (especially older nForce 4) also need extra power from one HDD power connector as well.

Obviously if you have a video card that has its own power connector you will need to attach that, too.


OK. It looks like the PSU. I connected just the 24-pin connector, and when I connected the suspect one to the known OK machine, it was dead. When I connected the known good PSU to the dead machine, it powered up the fans on the mobo.

That would seem pretty conclusive, I would think?

It does sound like it is the PSU, then, assuming the first machine could at least complete the POST successfully with the known good PSU.

Tony
19-05-2013, 08:03 PM
It does sound like it is the PSU, then, assuming the first machine could at least complete the POST successfully with the known good PSU.I didn't check whether it actually got through POST - I turned it off as soon as I saw the fans were running. I think the fact that with one PSU there was nothing and with the other there was something is enough to convince me the PSU is defunct.

Thanks everyone for the advice. All I have to do now is find a decent PSU at a reasonable price.

dugimodo
19-05-2013, 08:10 PM
If you're interested the reason for the extra testing is that the power on signal comes from the motherboard not directly from the power button so a fault in either the button, the wires, or the motherboard can act like a dead PSU.
Putting an earth on the green wire bypasses all that and just tells the PSU to power up.

Look at the wattage of your old PSU and go for a reasonable brand like the usual recommendations from here - corsair, seasonic, silverstone, antec, etc. You could go cooler master or thermaltake also but they are not as good and might not last the same or supply as much power as they claim. Stay away from the really cheap ones.

Tony
19-05-2013, 10:51 PM
Thanks for that, and also for the advice about PSU brands. My current (dead) PSU wattage is 560w, so I was planning on looking at 600-700w, to give me a little headroom, although this one has coped with all the usual stuff plus 4 HDD - except of course it is now dead. :)

Agent_24
20-05-2013, 02:07 PM
I didn't check whether it actually got through POST - I turned it off as soon as I saw the fans were running. I think the fact that with one PSU there was nothing and with the other there was something is enough to convince me the PSU is defunct.

I agree, and obviously you need a new PSU anyway - but the PSU could have failed in a way that damaged the motherboard, or even the other way around. If you didn't test that the machine passed POST with the good PSU, there is no guarantee that a new PSU will completely solve the problem.

Tony
20-05-2013, 03:11 PM
Well, I guess we'll find out when I get the new PSU :) - ordered from Ascent today and hopefully here tomorrow. This is what I ordered:

http://www.ascent.co.nz/productspecification.aspx?ItemID=400951

Tony
21-05-2013, 02:41 PM
I ordered the PSU lunchtime Monday and it arrived 9:45 Tuesday - great service from Ascent, as usual. :thumbs:

All installed and working - which is a relief.

Thanks everyone for the help.

wratterus
21-05-2013, 03:16 PM
Good choice.