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Strange PSU behavior

Last response: in Components
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February 21, 2011 11:36:28 AM

So here's the deal, I unplug everything on the PC, bring it in the kitchen install a new fan, replug it and the following happens each time the computer is ''unplugged''.

I press the power on switch, comp seems to boot up (you hear the fans the power led lights up etc) but then it shuts down. It stays down for 5 seconds then it starts back up and the computer boots no problem.

I tested it with only unplugging the PSU without moving the pc and it did the same thing.

I give the PSU 2-3 minutes to fill up it's capacitors too before pressing the power switch, but waiting up to 10 minutes (tried it once) does nothing.

It only recently started to do this too... I had this PC for 2 years and a half and dusted it each month and never had this happen until recently.

More about : strange psu behavior

a b ) Power supply
February 21, 2011 12:43:39 PM

Hi.

What are the rig's components? Can you test with another PSU?
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February 21, 2011 1:46:58 PM

MB: Asus P5Q (regular one) MCH=P45

CPU: Core 2 quad Q9400 (overclocked to 3.6Ghz 2.66ghz original clock) (max temp under load 57C) Stable

GPU: Asus EAH4870 512M memory (ati radeon hd 4870) not overclocked

HDD: 1 Green WD 1TB and 1 Green WD 2TB

PSU: Corsair TX750W

Case: Collermaster CM690

RAM: 2x 2GB DDR2 800MHZ kingston Overclocked to 903MHZ (451FSB)

Windows 7 professional 64 bit (kinda meaningless since it all happens before windows attempts to load though)

I don't have a spare PSU with me unfortunately... I'd have to buy one to test lol.

On another note, my brother's rig is almost identical to mine (he isn't overclocked, has 1 hard drive and windows XP) and his PSU just failed recently so he has to replace it lol.

Have to say I took care of mine alot more than he did, his computer was incredibly dust clogged.
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a b ) Power supply
February 21, 2011 1:54:54 PM

Down clock your RAM and try again.
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February 21, 2011 2:35:01 PM

I took down my overclock from 3.6 to 3.2 which reduced Ram speed to 800MHZ. Ram wasn't overclocked but the problem presisted.

I then loaded setup defaults in bios and changed stuff like boot priority and turned off Floppy drive and the problem went away??

I can only conclude that it's the MB's bios that behaves strangely with certain settings. I'd have to mess around with them 1 by 1 to determine which one does it.

Do you think I should try to correct the problem? Can starting, shutting down and restarting damage my PC's components? (it would happen a couple of times a month (4-5 max))

I was afraid that it meant that my PSU was failing, but I ran OCCT power supply test (loads CPU and GPU to 100%) for 30min no problem so it can't be that it has a hard time handling the load that booting up demands.

Thanks for your help so far, I didn't think that it was linked to my overclocking at all.


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a b ) Power supply
February 21, 2011 2:46:42 PM

or a short between mobo and case.
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February 21, 2011 3:03:32 PM

Since my computer works perfectly except from that it can't be that there's a short somewhere right? And the MB is shorted to the case by the 6 screws (for the GND) but if something else was shorted by some way the consequences would be a lot more dramatic right?

I might have misunderstood your answer though (I'm kinda paranoid lol).

I'll be away for something like 4 hours and won't be able to answer or read posts until then.
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a b ) Power supply
February 21, 2011 3:16:03 PM

Nevermind, it's not a short.

You have a good PSU, but if you can test with another PSU.
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February 21, 2011 4:48:07 PM

If I can put my hand on one I'll try it, thanks for your help.
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February 21, 2011 4:48:15 PM

Best answer selected by thyrokio.
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a c 243 ) Power supply
February 21, 2011 6:01:50 PM

thyrokio said:
So here's the deal, I unplug everything on the PC, bring it in the kitchen install a new fan, replug it and the following happens each time the computer is ''unplugged''. I press the power on switch, comp seems to boot up (you hear the fans the power led lights up etc) but then it shuts down. It stays down for 5 seconds then it starts back up and the computer boots no problem.

I tested it with only unplugging the PSU without moving the pc and it did the same thing.

I give the PSU 2-3 minutes to fill up it's capacitors too before pressing the power switch, but waiting up to 10 minutes (tried it once) does nothing.

It only recently started to do this too... I had this PC for 2 years and a half and dusted it each month and never had this happen until recently.

http://en.wikipedia.org/wiki/Fake_boot
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February 21, 2011 6:24:16 PM

Ooooh! this explains it then lol. Thanks alot.
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!