[SOLVED] Unwanted PC Boot when AC applied

Hy guys,

I'm in need of a little help here. I have a Corsair CS650M PSU that's acting up. It's a bit of a less commen set up, so I must give you a bit of a premise.

It's in a PC running a [email protected] @ 1.28V on an Asrock Z77 Pro4, with an nvidia 210 passive GPU, an SSD and a HHD. It's a Pc for audio prodution, nothing fancy.

The whole studio runs on a separate Thermodifferential switch (I am not sure how to call it in english, RCD?) with two separate sub circuits, one for the power outlets and one for the lights. Well, basically the studio owner shuts off the power outlets every day using a 'master switch' in the power box and shuts the lights off with a normal switch (so not to disable the lights in the whole structure).

Well, the problem with the PSU is this: the guy shuts off the PC normally, then shuts off the 'power outlet' master and leaves. When he powers on the outlets, the PC boots up on its own. That is a bit of a problem since the audio interfaces are off and need to be on before powering the pc on (still using firewire unfortunately).

The PC works just fine, the OC is stable and this strange power on behaviour is just a nuisance, but requires the owner to shut down the pc, power on the interfaces, masterclocks and so on and THEN power the pc on again.

I tried connecting the PC directly in one outlet instead than in a powerstrip. No change.

Could the spike from the master switch boot up the pc? Isn't that a sign a faulty PSU, discharging tension on the mobo? It could be worth noting that if the master switch is turned on and off in brief intervarls, the pc won't boot up on its own. It does so after longer periods of 'power off'.

Truly sorry for the lenghty post! Hope you can give me some pointers.


get a volt meter and and read the voltage form the wall when it is turned off and when it is turned on. then plug in a "off" device like a lamp and read the voltage going into it when on and off. my guess is the problem is you are getting a surge when the flip is switched. you only need a small surge to start up the computer then the psu will start drawing more.

BIOS setting, don't remember what it's called but it's for what happens after power outage.
That one is set to power up after loss, just change it to stay off.


That would be my guess too.

Mine (asus) is called, "Power on after AC Loss" and is buried somewhere in a uefi submenu.

Could also be a PSU issue.

FWIW, a friend of mine also has a similar problem with his PC; however, for him, shutting down Windows yields a clean shutdown, while shutting down Mac OS yields a reboot.

My bet is on the uefi setting.

And ain't nothing wrong with firewire. ;)

OK, did some googlin..
Look for "Restore on A/C power loss"
It's under "South Bridge Configuration" on the Advanced screen.
Set it to [Power Off]

Yeah, my bad, I should have said that I did check the BIOS setting first thing, and the restore after AC loss is off.

@fredrich_nietze good idea, I'll try that. But wouldn't the PSU AC inlet line filter (sorry, I only know the technical term in italian for it and I am roughly translating it) use some sort of capacitor array to filter these spikes out?

Cheers boys, thanks for all the answers.

Firewire is a bit... temperamental at times! A long time ago one of the ports on my Focusrite fried because of a bad shoutdown! Still, back then firewire was new! But hey, where would the fun be otherwise?! :P

Thanks for taking the time to answer mate.

in theory yes in practice, it depends on the strength of the surge and corsair may have cheaped out on them or they may be faulty.

Yeah, thought as much... I'll go back to the studio tomorrow and have a little test. Thanks again!

A closing thought on the issue.

After checking for unwanted spikes on the line, I could find none. No strange spikes in tension or intensity. Everything as it should... I took the PC home and it did the same thing on a switched power strip.

I contacted Corsair and the issued an RME, no questions asked. Defective PSU.

Again, thanks everyone for the help! :) :)