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PC Turning off problem - PSU problem

Last response: in Components
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April 30, 2007 10:33:52 AM

Hi, i have a very strange problem. I built a P4 3GHz with gigabyte 945 motherboard about a month ago and have been running without any problems till today.

Last night my computer turned off whilst i was asleep, i tried turning the PC on in the morning by the switch but nothing. I had to physically remove the power from the PSU, wait 10 seconds, plug it back in, and only then would the PC turn on.

Unexpected shutdown was listed in the event manager, i thought it may have been a software problem. Soon after that whilst in windows it turned off (not crashed, i mean straight down to dead). I had to remove the power lead again before i could turn on again.

I then turned on and went into the BIOS to check temps. Then inside the BIOS it shutdown! Whaaaaaaa.

I then left it for 30 minutes, booted up a memory check program and it ran fine for an hour. If it were memory or CPU problem i would expect the PC to crash and freeze, not just turn off. The CPU temperature is 50 degrees and doesnt get over 60 degrees. I hate intermittent faults like this.

I've seen strange problems from building PCs over the past years but this has me a bit baffled. I think it may be temperature related as it was fine after being turned off for a while. I'm thinking the culprit is either the PSU or motherboard?

The PSU is a 700W thermaltake, and the mobo a gigabyte, both were running perfectly. Why the sudden break? I havent moved or touched the PC. I need to prove which componenet is knackered so i can get a replacement.

PS is there any good burn-in test software that runs from a boot disk? I want to try and reproduce the fault but not boot into windows (im afraid the constant turning off will knacker and corrupt my data).

Thanks for the help in advance,

Chris
April 30, 2007 10:52:05 AM

Hi, no brownout as i know it but i wouldnt be supprised! I am on a surge protection plug however. It only happened last night.

Regarding testing of the PSU, i presume the green wire needs to be grounded to turn the PSU on? However, this fault is intermittent, and the PC is turning on -sometimes!-, so this wouldnt test for this case would it?

The PSU crossbar is being activated, which i presume is an overvoltage or overcurrent condition as its only re-enabled after removing the power.
April 30, 2007 12:28:49 PM

I think you try replacing the power supply. If it does not solve the problem take it back to the store.
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April 30, 2007 3:56:09 PM

Quote:
If the PSU can maintain power on its own then it's not the PSU and the fault lies with the motherboard. Just because something is damaged doesn’t mean the problem will be consistent. If you still think it's the PSU then you will have to try a different PSU. It's about the best way to test it. Chances are though it's the motherboard having problems. Even with a surge suppressor a brownout can still damage a system. The surge suppressor only helps prevent surges and only at it's rated capacity. Brownouts are low and inconsistent power and only an uninterrupted UPS can prevent damage from a brownout. Check you motherboard and pay close attention to the capacitors. If any are bulging then that is your problem. This would explain a lot as they would not be able to hold a charge properly and would be discharging at irregular intervals.
Sure, but there is some sensing circuitry inside the PSU. for instance there will be current sensors detecting short circuit conditions. as mentioned when the pc turns off randomly the psu doesnt turn back on until power is removed and pluged back into the psu, this means the psu crowbar is coming in as its protecting against a short. something is drawing too much (its a 700W supply and i dont have a beefy graphics card or lots of drives) so the only thing it could be is a short, OR the current sensing circuitry has gone a bit nuts and is causing it to trip out.

I havent moved the case, and now its been running prime95 fine for the last 2 hours. cpu temp hasnt risen above 52 degrees. if it were a short my prodding and pushing of the motherboard whilst its running would reproduce this fault right? unless im mistaken i strongly suspect the psu electronics inside, OR maybe the ON switch is bust as that has always stuck down on the odd occasion (it would spring back up, plastic got stuck). However, that wouldnt explain why it would go down after an uptime of 15 hours?

very very confused, i hate intermittent faults which i cant reproduce!
May 1, 2007 1:33:08 AM

Make sure the motherboard isn't shorting somewhere did you use all the screw standoffs or just screw it straight to the case ?
May 1, 2007 7:27:24 AM

yeah the mobo is screwed with all the standoffs, and my pushing of the motherboard would reproduce this fault right? No matter how much i push or apply light/medium pressure it is fine.

Its deffinetly a temp issue or similair, its ok to start off with (as with testing last night), i left prime95 running and when i woke up it was dead again!!

Checked the caps all look to be fine. Are thermaltake PSUs a bad make? I checked the voltage from the gigabyte utility and it they remain rock solid even when under full load.

Cheers,

Chris
May 1, 2007 7:32:14 AM

*watches thread like a hawk* [/is having a similar problem in a system somewhere]
May 1, 2007 8:31:38 AM

Mugzy, so you do know there is a hardware section.
May 1, 2007 10:12:25 AM

Quote:
I then turned on and went into the BIOS to check temps. Then inside the BIOS it shutdown! Whaaaaaaa.



Could be one of 3 things when it happens in BIOS.
1) PSU
2) RAM
3) MB

Try only 1 stick of ram at a time...if issue stays then eiter MB or PSU is at fualt.

A bad CPU could do this also....but if that was the problem I doubt you could enter BIOS at all.
May 1, 2007 10:15:23 AM

sure thing however memtest passed 5 times ok, im sure the ram is ok. furthermore, ram would lead to reboots and freezes, not complete power loss right?
May 1, 2007 10:28:33 AM

Quote:
not crashed, i mean straight down to dead


Sounding more like a short or PSU issue now that I re-read that part.

Try unplug everything but the MB and see if it stays in BOIS by it;s self.
Unplug also means all the cards exept the GFX card, If it still crshs at that point swap the GFX card and test.

If it still crashs and you have also used only 1 stick of ram (and changed slots/stick) then either the MB or PSU is screwed.
May 1, 2007 12:38:48 PM

I was going to say ^^^ what he said. I've had hard drives take out a rail along with a bad CD drive, etc. Takes the whole computer down. Unplug everything connected to power except the mobo, CPU fan and keep the ram installed.

I think one of your components might be taking out a leg. Usually if it a PSU, it stays dead. It doesn't "fix" itself for a while, then fails again. I'd be taking a close look at a Hard drive or CD drive - most likely components.
May 1, 2007 7:26:32 PM

thnx for the replies guys. heres what i did

tried both sticks of ram, 1 at a time
unplugged power from all usb headers on the case
unplugged all drives apart from hard-disk
removed all pci cards
removed all case fans

i was left with just the cpu, 1 stick of ram and psu, it still crashed. i have since changed the psu and it *seems* to be ok. fingers crossed. i will let prime95 thrash the system over nite and hopefully it will remain powered by the morning.

i reckon the overcurrent sensing circuitry has gone nuts, fingers crossed this is it. cheers guys
May 2, 2007 8:14:48 AM

This is how I slipped into the club without getting the attention of the bouncers. My first 300 or so posts on these forumz were in Hardware.
May 2, 2007 12:18:35 PM

Have you disabled the, shut down on errors in bios. Second disable any power saving features in bios. These features can cause similar problems
May 2, 2007 1:13:48 PM

The Other?
!