Power supply switch starts computer

magicanthony · Oct 27, 2016

Just build a new computer. Other than some issues I had, all seems well now.

Anytime I would do something inside, I always shut down, turn off power supply switch, pull out plug, and hold case power button for a few seconds to discharge. Then do everything in reverse.

I just installed windows 7, now when I do the above, when I turn the power supply switch on the computer boots without me having to press the case button. I checked the BIOS settings for power on after power failure and it is disabled. I haven't changed anything in BIOS. Any idea why this suddenly changed? Is there a setting in windows 7 that would make the power supply start the computer?

Thanks.

Full specs of PC:

OS: Microsoft Windows 7 Professional SP1 64-bit - OEM
CASE: Corsair Carbide Series 200R Black ATX Mid Tower Case
CASE FANS: (2) 120mm front intake, (1) 120mm rear exhaust, (1) 140mm top exhaust
MOTHERBOARD: ASUS Z97-A LGA 1150 ATX
CPU: Intel Core i7-4790K Devil's Canyon Quad-Core 4.0 GHz
CPU Cooler: Phanteks PH-TC14S, Slim Twin Towers, 140mm
MEMORY: 32gig - CORSAIR Vengeance 16GB (4 x 8GB) DDR3 1600 SDRAM (PC3 12800)
VIDEO CARD: GIGABYTE GeForce GTX 960 4GB WINDFORCE 2X OC EDITION
PSU: CORSAIR AX Series AX860 860W 80 PLUS PLATINUM
OPTICAL DRIVES: 2 x LG WH16NS40 BD Rewriter 16X Speed
HARD DRIVE1: SAMSUNG 850 PRO 2.5" 256GB SATA III (SSD)
HARD DRIVE2: Western Digital Black WD2002FAEX 2TB 7200 RPM SATA 6.0Gb
MONITOR: Samsung S27E650D 27" LED LCD (1920x1080)

greens · Oct 27, 2016

You shouldn't unplug your PC when you're working on it. Turn the PSU off, but do not unplug it. The outlet is the only way for you to have your PC grounded, and a grounded PC is 100% immune to static shock.

It is probably your momentary switch. Disconnect the front panel connectors from your motherboard, and flip your PSU on. If it doesn't start, you know something is wrong with your momentary switch (power button).

magicanthony · Oct 27, 2016

I was using an antistatic wrist strap and always touch the case before doing anything. The thing is, it wasn't doing this before. I tried a bunch of times and once it didn't do it but otherwise it always does it now.

I tried repeating the procedure with the case button disconnected and it still did it so it's not the case button. I also tried disconnecting the hard drive and still no change.
I just don't know why it started doing it when it didn't before.

And I've read it's better to unplug the cable since there is still some power to the motherboard. I have always unplugged computers when working on them and never had this problem.

Thanks

greens · Oct 27, 2016

If you are at an imbalance with a computer, and you attach a wrist strap to it, you will discharge into it, then be balanced. This initial discharge is usually mitigated by the case, but could potentially cause damage. There absolutely are charges in the power supply capacitors. Unplugging it from the wall, switching the Power supply off, and holding the power button, do absolutely nothing to discharge the capacitor or mitigate that risk. Motherboards do not have any dangerous loads.

I don't want you to remove your whole PC from the case... but it sounds like there could be some kind of short. Did you use correct motherboard stand offs in every location for your motherboard? Did you remove all stand offs that aren't aligned with your motherboard? It sounds to me like you have some kind of short - your case is acting as a power button all on its own. I've seen plenty of PCs turn OFF at a touch, but not usually instantly on.

Does it turn off normally? power button works to turn it off? Doesn't turn off if you touch the PC or anything?

magicanthony · Oct 27, 2016

greens :

Ok I tried a few things and I may have figured out the reason. Let me know your thought.

First I'll answer your questions:
- The standoffs were already installed in the case and all lined up with the motherboard. There were no extra. I made sure everything fit correctly and nothing fell under the board. I also made sure none of the I/O shield ground tabs fell into ports (this is actually my 7th PC build).

- It turns on and off normally. Nothing happens if I touch the case while it is on. It doesn't shut off on it's on and doesn't turn on by itself.

This is what I noticed. After doing my procedure, the power light on the motherboard was still on. I just tried twice, waiting for the power light to go off. Then it doesn't happen. So I'm thinking that as long as the motherboard still has charge in it, flipping the switch starts the boot process. But once it's completely discharged, then it doesn't. All the previous times I think I worked in the case longer which gave it time to discharge. The last time was quick, and all the subsequent times where I was testing it I did it quick.

Could that be it? everything else seems good. All connections are good (I unplugged and re-plugged the 24 pin connector), nothing seems like it could be shorted, and the computer seems to work fine.

Thank you.

greens · Oct 27, 2016

magicanthony :

Well, most PCs do maintain a motherboard power LED even when off.

My thought now is that the starting circuit on the PSU could be fried. If you unplug the 24 pin from the motherboard, does the PSU spin up all on its own? If the PSU fan spins without any cue from the motherboard it is certainly the culprit.

You didn't install a jumper on that PSU and forget about it did you? No extra loops on your 24 pin connection?

magicanthony · Oct 27, 2016

greens :

Not sure what you mean by installing a jumper on the PSU. I didn't install any jumpers. I looked at the 24 pin connector and it looks ok. The PSU is in hybrid mode so the fan doesn't spin unless it has to. I suppose I could switch to the other mode which I think keeps the fan on all the time, and then try with it not connected to the motherboard.

However, if the starting circuit was fried, wouldn't it happen all the time? I just tried it 4 times, waiting for the motherboard LED light to go out, and it didn't start until I pressed the power button.

UPDATE: I just tried the same thing with another computer of mine, in which I never had this happen. I shut down (from windows), turned off power supply switch, held case button for a few seconds, and unplugged power supply. I then plugged in the power supply, before the motherboard light went out, and turned on the switch and it automatically booted.

I did it again waiting for the light to go out, and it didn't boot. So it looks like if you turn off the power supply switch, and then turn it back on while there is still power to the motherboard, it will reboot. I've never noticed this before, I guess cause I usually take longer to work inside a computer so there has always been enough time for the motherboard to discharge.

If there is any way for you to test this I would love to know if this is normal procedure.

Thank you.

Search

Power supply switch starts computer

magicanthony

Distinguished

greens

Splendid

magicanthony

Distinguished

greens

Splendid

magicanthony

Distinguished

greens

Splendid

magicanthony

Distinguished

TRENDING THREADS

Latest posts

Moderators online

Share this page