System shuts down randomly and won´t POST for 15 minutes

Som3one · Sep 30, 2013

Hey there,

I´ve already opened a thread for this issue but I thought I have solved it. Turns out I was wrong.

First of, here´s my system:
CPU: i7-4770k @ 4.2GHz, 1.2V Vcore
RAM: 2x4GB Corsair Dominator Platinum 2133MHz @ 1.5V
Motherboard: Asus Z87 Sabertooth (BIOS 1405)
PSU: Corsair AX760i
CPU Cooler: NZXT Kraken x60 with Noctua fans
GPU: Gigabyte GTX 780 Windforce Rev 01
Storage: 1 x 250GB Samung 840 pro, 1 x 500GB Hitachi HDD, 1 x 3TB WD Red, Asus DVD writer
Fans: 1 x Corsair AF140, 2 x Corsair AF120L, 2 x BeQuiet Silent Wings 2 120mm

Now for the problem:
My system randomly shuts down without any error message or BSOD. After that - without having to hit the power button - it turns back on. Which means all the fans start spinning etc. but it won´t POST. Then it shuts down again and repeats the whole process. This usually happens 3-6 times before it shuts down completely.
The only way to get it back up again is to pull the power plug for about 15 minutes. It usually starts up with a "Overclocking failed" error message but works fine after that.
Sometimes this happens two days in a row, sometimes it works fine for 2-2.5 weeks. It happens no matter if I run it overclocked or at stock settings (CPU and RAM). It always happens when idleing or doing light work like word, firefox and the like. But it has never (!) happened while under load.
Also, I am not able to reproduce it which is really depressing.

I´ve already reconnected all the cables and it still happens. And since it won´t even POST after a shutdown suggests it is not a software issue but rather a hardware issue.
And since it sometimes runs fine for 2-2.5 weeks I can´t really check if it works with a minimal configuration.

I am thinking about RMAing it...but the question is...what should I RMA?
My guess is that it is an issue with the PSU and/or the motherboard. But it could be anything.

Any advice is appreciated.

palladin9479 · Sep 30, 2013

Most likely the PSU has problems. Are you able to get a hold of a different known good PSU to check it against?

Som3one · Sep 30, 2013

Unfortunately not. At least not for the 3 weeks or so it would take to test it.

Som3one · Sep 30, 2013

One more thing while we are on it:I always suspected it to be an PSU issue, too.
But how would explain the fact that it won´t POST for 15 minutes after pulling the plug?

palladin9479 · Sep 30, 2013

Capacitor discharge. The PSU and MB have many capacitors that hold a charge even after the system's power is cut, they often take awhile to fully discharge.

Som3one · Sep 30, 2013

I´ve got one (last?) theory besides a faulty PSU/mobo. I could be wrong but I think those shutdowns could have happened only when I had my external HDD hooked up.
I disconnected it and we´ll see what happens...or if anything happens.

If it happens again I will contact the online shop I got the PSU and mobo from and I suspect they will advice me to send both in for an exchange.

joesklar · Sep 30, 2013

The exact same thing was happening to me recently. The best thing that helped me was discharging; to do this remove the kettle lead from the PSU and hold down the power button for around 30 seconds. This was a quick fix so that I could access BIOS, after that I had to clear CMOS and eventually replace the CMOS battery.

Try both of these things including replacing CMOS, the batteries are only a few pennies.

Also, try a KNOWN GOOD HASWELL COMPATIBLE PSU. Refer to this list for full compatibility: http://techreport.com/review/24897/the-big-haswell-psu-compatibility-list

Good luck, be sure to keep us updated.

Som3one · Oct 1, 2013

joesklar :

Already tried that but didn´t work.

joesklar :

Hm....you think this could be the problem? I mean the board is like 3 months old or something.
I think I have a spare battery laying around from my old mobo.

joesklar :

Mine is compatible.

joesklar :

I will. But if the past months has tought my something, it probably won´t happen again for the next 2-2.5 weeks until I feel like I have found the problem and then it will shut down again.
My system is quite sardistic.

Thanks for the help.

Som3one · Oct 7, 2013

A little update:
I ruled out the external HDD as a cause.
Also, just to be sure, I ruled out the wall plug.

But yesterday I was lucky. It happened while my case was still opened up. After the system turned off I performed a self test of the PSU and it didn´t pass. So, it´s obvious now that it really is the PSU.

I already contacted the reseller and will send it back in the next days.
Just thinking if I want a replacement unit or if I should go for a completely different brand/unit.
Currently leaning towards the latter.

Som3one · Oct 11, 2013

Another update:
I decided to exchange my Corsair Ax760i for an EVGA SuperNova 1000 G2...which - for some reason - is also cheaper.
Should arrive today or tomorrow.

Som3one · Nov 3, 2013

Just for the record:
It seems like the PSU really was the cause.

Thanks for your help.

Also, I decided to go back to the AX760i. The SuperNova was too loud for me.

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