Spontaneous power?

Aloha, electricity gurus. I recently decided that my case was too cramped, hot, noisy and ugly and so I moved my system lock, stock, and barrel into a new case with a new power supply.

Those figures:

Lexa NZXT case (mm, nice)
Enermax 480W EG485AX-VHB(G) SFMA V2.0
Plugged into a slightly ageing ASRock K8 Combo-Z with an Athlon 64 2800

Well, I want to futureproof a bit.

All goes well until I plug into the wall and flick the switch. Then, the internal fans spark into life for a moment, but otherwise everything seems to be in order. I can power up and get into Windows and everything. Internal temperatures are nice and chilly at 25-30*C idle. I apparently suffer from no ill effects re random restarts, hardware failures, or sudden bouts of leprosy.

If I leave the system off but plugged in for any length of time, though, the whole thing sometimes spontaneously starts up, fans, HDD and all. Then just a second later, it shuts off and cannot be turned back on with the power button. I have to unplug it for a minute or two and wait for it to calm down.

I've used MBM5 and the BIOS setup to have a look at the voltage readings and get the following on idle and after half an hour of high 3D use:

1) (core) 1.55 apparently stable
2) 2.05-2.10
3) (3.3v) 3.34 apparently stable
4) (5v) 5.19 apparently stable
5) (12v) 12.28-12.34
6) 2.86-3.02
7) 3.70-3.85

These are pretty stable and appear to be within the usual 5% tolerance, but the BIOS reports the 12V to be 12.5 which is on the cusp.

Any ideas what's going on here? Is my PSU a bit overactive, silently hoarding the leccy until it actually powers itself up? Can that even happen?
20 answers Last reply
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  1. I doubt that this is the PSU hoarding trons and then using it to randomly boot your PC - I don't care how much the sucker likes to play Guild Wars. Are you using a UPS? Have you checked the power management settings in BIOS and Windows.
  2. No UPS, just a three pin power cable slapped into the wall with a clean enough power supply. (I've tried it in another socket just to be sure.) The BIOS "power on when..." settings are also disabled. The system even powers up if I unplug the case header pins, so something *somewhere* must be triggering it.
  3. As unlikely as it may have seemed I also thought about a faulty power button. Disconnecting the power switch button eliminates that if you still get the power up with them disconnected. This really sounds like a power management issue. You disabled those functions in Windows, too?. Is it connected to a LAN or broadband? If yes, then try disconnecting both and see if you still get the start ups...
  4. Everything power-related is disabled in the BIOS and Windows, and there's nothing that should cause it to boot other than the power button. I'm currently testing its magic self-powering abilities by, er, having it plugged in while I have a nice cup of tea and a go on Mario Kart, and it has yet to start up like it did yesterday.

    So, currently my system is capable of running on load for a few hours without issue and sitting silently while plugged in without issue. Is it possible for a PSU to take time to "settle in"? Residual current or something? I'm not going to take any chances and leave it plugged in while I'm out, but annoyingly everything seems to be working at present.
  5. Nothing that I know should cause it to boot if all of the power managerment features are turned off. The reason that I asked about the LAN/broadband was in case you had Wake On LAN (WOL) enabled and possibly getting hacked or the feature was faulty... If it continues to happen then I would consider flashing BIOS and definitely post in the mobo mfrs forums or contact them via other means.
  6. That's the thing, though. It's a lock stock transfer of my old (working) components. The only new bits as far as the mobo should be concerned are the huge power cables and exciting new on button. That coupled with the fact that the system appears to be working right now - it hasn't turned itself on in the past few hours - means I don't really have much to go on. I've sent messages to the PSU manufacturer and the reseller. I might try the mobo guys too if it happens again.
  7. pretty interesting scenario you got here. so i think its pretty safe to assume that this problem just started when you started using the new case.

    if you can load into windows and play games then i think your problem would be more cosmetic than your actual hardware.

    double check to make sure your power button and reset button conenctors are correct on the motherboard if they are switched say + to - that may cause problems not like the one you described of it actually powering on.

    try checking all case wiring that plugs into the mobo.

    also im sure its not as simple as this but, how do the power and reset buttons feel when you push them? is there a springy resistance? and do they pop all the way back out after you press them down?

    this sounds like a problem with the case wiring.
  8. The buttons feel buttony enough. Reset is reassuringly clicky, and the power button carries enough weight to make me believe it is doing its job correctly. But it can't be those, because the system auto-powered up in my tests when the buttons weren't even connected. Yesterday, I had a system that either wouldn't power on or would spark into life without human intervention. Today everything is irritatingly stable. And you should never trust a problem that resolves itself.
  9. well its not resolved its just not as aparent.

    and the fact that it powered it self on without the buttons connected to the mobo is beyond me.

    and this wasnt happening in the other case?
  10. In my professional opinion, i think you should get a priest to perform an exorcism on that box. lol.

    Just some things to shoot out there, since all that really happened is a PSU switch, and a case switch:

    1] Did you mount the motherboard to the case using the supplied risers? If you have the motherboard screwed right into the side panel, the it would more likely short out, but ive never seen this problem before so its just something to check.

    2] If you have all the mobo headers (USB, IDE, FDD, POWER, AUX Power [4 pin for CPU if it applies], Front Panel connections incl. power-reset switch) try unplugging them all, and just plug in the power connector (20 or 24pin) to the mobo, if it dosnt start up on its own, try plugging things back in 1 by 1 until it powers by itself.

    I know that this has the potential to be quite the process, unless someone has actually come across this problem before then i think you have a bit of a headache on your hands, as well as a long trial and error session.

    Another thing that you can try...is to mount everything back in your old case (with the new power supply) and see if it happens..then you can somewhat narrow it down to the case or PS if it happens even in your old case.

    Just some thoughts...i have never come across this problem before but I definetly offer any knowledge i have to the solution.
  11. or just use the old psu in the new case, save alot of time and essentially be the same test.
  12. >> In my professional opinion, i think you should get a priest to perform an exorcism on that box.

    No chance. It took me a good many years (and a couple of spoons of blood) to get the spark of life into my system and I'm not about to kill her off now. Maybe she's just freaking out from being put into a new case without warning.

    1) Mobo risen. Like I say, once booted there is no apparent problem at all. No unexpected shutdowns, no sudden hardware failure, no magic smoke.

    2) This is what I spent most of Monday doing. I originally attached the 20p and aux 4p leads alone and couldn't get it to power on, then I found out that using the auxilliary connector won't work if there aren't enough devices installed to suck up the power. I hooked up a few more things and electricity started flowing. The problem is, it sometimes starts flowing without the need for a power button.

    Hooking up the old PSU and/or old case connectors seems to work, but then the new PSU/case seems to work too. It has gone all evening closed in the new case without issue. If I bumped my head and forgot everything that happened on Monday, I wouldn't know there was anything wrong with the system.
  13. In ATX systems the on/off state is asserted by a logic level on a specific pin rather than the button actually routing big power like in AT. There is a pin for this which goes to the on/off button. It is possible that you may have inadvertently brushed some low resistance object between the on/off pin and some other pin which contained the logic level necessary to transition states from off to on.

    Edit: BTW the necessary logic level to transition from on to off and visa versa will be located on a pin directly adjacent to the on/off pin, and so this move is really easy to do. In fact I use this alot when building systems to do preliminary checks before going through the work to hook everything up.
  14. Well, thanks for your help. I'm tempted to put it down to some silly unknown error (bit of dust, dodgy power button, a lead not pushed all the way in) that I've inadvertently fixed along the way. I can't reproduce the problem now.

    If it were anything but the PSU in all of its potential component-blowing data-losing fire-starting glory I wouldn't have been so concerned.
  15. I know you didnt have a problem before from your Enermax but I am getting my 3rd RMA'd PSU from them. first one lasted 2 months, second one lasted 30 minutes. They might send me a different model this time. I hope tired of the EG565- I am so burned on them right now, if it says Enermax , toss in the trash.

    not really but I hate to call it quits on a 109 dollar PSU it would be nice to have a reliable spare even though I have replaced all of my power supplies with another brand.
  16. Ahhh, the wonderful intermittent fault! Has it happened since you pulled/reinstalled the case wiring from the mobo? Maybe you had something on wrong...
  17. assuming you have wired everything ok..and did everything posible in software (bios and os)....you have two options

    1 - remove all the pci expansion cards..modems can trigger your sistem on when you plug the cable .....

    2 - if there are no expansion cards.....you could just replace your psu with another one and see what happens .... psu in on when grounding (Low logic) the green wire (psu_on wire)......14-th pin on 20 pin atx and 16-th pin on 24 atx cords

    good luck
  18. Quote:
    No UPS, just a three pin power cable slapped into the wall with a clean enough power supply. .....

    I suspect this is the source of your problem.
    Go get a surge protector. Preferrably one with a "connected equipment guarantee"

    im also guessing that your house lights dim whenever the fridge or washer kicks in. Power spikes and surges could be triggering your PC to turn on.
  19. I have a surge protector. When the system failed, I plugged it straight into the wall instead to see if that was the problem.

    "im also guessing that your house lights dim whenever the fridge or washer kicks in."

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