Changed PSU,when connected 24pin,no power

Dwarf said:

You DON'T bridge the purple and black wires! The purple wire is the +5VSB (StandBy) line, and all I wanted to know was if there was actually any power present on this line and what its value is.

I note that unconnected there is 4.56V present, but connected only 2.25V. For the latter reading, is the system powered on or off?

Disconnect all peripherals, especially those that are USB, and also disconnect any that plug into motherboard headers (including FireWire, if present). What voltage do you get on that line now? If you monitor it as you disconnect things, you might even find the culprit (it could be something as simple as the mouse). Something somewhere is causing that voltage to drop to a level where it cannot power the logic circuitry that controls the function of the power button.

I know,i wrote the wrong color,it was ofcourse the green wire. for the 2.25v the system is off,but 24 pin connected as is 4pin 12v,and power button on psu is on.

Oh,and i cant get it to start even with nothing connected,not even ram. I had tried this before though,removing everything,and only adding one thing at a time,it dont work.

Is it not normal for the voltage to drop to 2,25v when connected to mb? Also,if this happens,i suspect either the psu is just too old for ths newer board,or the psu is not as high quality as it was sold as once upon a time,and thus cannot keep the voltage to boot levels

Dwarf said:

I don't believe that is normal. What readings are you getting on that line in your other machine?

The corsair gs700 deliver 5.11v simply connected to the mainboard. It must be the psu, as i could power the mb easy enough connecting it to the corsair,and bridging the mb power switch header. Is it simply enough it has to power a core i5 and not the amd phenom II x2 it powered before,to force it to behave like this?

I am gonna chuck this northq psu out,and i already ordered a new Corsair TX650 V2,so now i just hope i havent damaged any components on my mainboard with all this testing,removing and re attaching going on.

Thank you all for your help

Dwarf said:

It shouldn't make any difference, as the sole purpose of the +5VSB is to power the logic circuitry that controls the function of the power button (together with WOL and other standby functions).

If you swap the PSUs back over (you said that the problematic unit worked in its original system), what voltages are you getting on that line then?

It is quite possible that it is the PSU, and that the +5VSB circuitry within it (transformer, regulator, etc.) is beginning to fail and isn't able to maintain the correct voltage output when under load.

You know the saying "if it aint broke,dont fix it"? I am not gonna put this "faulty" psu back on its original board,as i have spent too much time getting the other systems to run perfectly.

If this psu cant keep the voltage to its designated power on a board that runs fine on a different psu,then by that logic,the psu is bad.

And since i already ordered a new one, i am not gonna spend any more time on it..

Thank you though for all your help, even though it might not be satisfactory i just throw the damn thing out .. Must be a reason no one sells north q psu´s anymore

Found this on wiki

Cheaper and/or lower quality power supplies do not follow the ATX specification of a separate monitoring circuit; they instead wire the power good output to one of the 5 V lines. This means the processor will never reset given bad power unless the 5 V line drops low enough to turn off the trigger, which could be too low for proper operation.

Dwarf said:

That sounds reasonable enough to me. Hopefully your new PSU will perform as expected. If you want a decent unit, see if you can get hold of the model listed in My System Specs. The actual unit itself is manufactured by Seasonic, who are one of the leading PSU manufacturers, and whose units are typically rebadged and sold by the likes of PC Power and Cooling (as recommended by Scott Mueller of Upgrading and Repairing PCs fame) as well as others (including mine, XFX).

850w is a bit much though,and the same model but in 650w cost the same as the corsair i ordered. I already have a corsair,and it is working great,which is why i ordered another corsair,plus it has 5 year warranty.

And i am sure the new psu will power this system nicely,unless i fooked up something and fried the rams or cpu or something,but if that has happened,i would still need a new psu,so either way,it is all good