This problem has baffled everyone...

[BigStan]

He means bad capacitors. Sometimes they go south and cause instability. Link
here ->

http://www.motherboardrepair.com/

 

[Nick G]

thanks. caps on both boards look fine. no leaks or discolouration.

 

[Mantric]

Thanks for your response. Answers/comments below:

the 400w PSU is made by Q-Tec and is not running the monitor (separate
power). It is the recommended PSU from Maplin (a specialist UK
tech/electronics components company). I dont think i need more than 400w as
i simply do not have enough components to require that power. however, i do
accept that given the symptoms it may well be that the psu or some other
power problem is at the root of this. The chances, however, of encountering
exactly the same problem with two different PSUs seems remote.

Can I just chip in here and suggest a different PSU as maplin know jack sh%# about
anything to do with computers. I have a variety of PSU units here that caused problems
similar to yours and two of them are newish Q Tec 400 watters.

You can get a resonable 400 watt unit made by Nexus from Novatec for 55 quid.

 

[~misfit~]

It was tested in two different properties in different parts of
London and on multiple mains sockets. I am writing this in one of
those properties and on a working laptop which is being mains powered
with no problems. The most bizarre thing about this problem is that i
have replaced every single major component at least once if not twice
and have still got the problem!

Including mobo? I still think you need to study the capacitors, maybe test
them.

 

[Russell]

I agree...get a "reputable" PSU to troubleshoot with. All symptoms point
most likely to a PSU not up to snuff. I recommend an Antec, Enermax or Sea
at 400W or higher, and plug it into a UPS as well.

Russell
http://tastycomputers.com

 

[~misfit~]

thanks. caps on both boards look fine. no leaks or discolouration.

No bulging either? Top or sides? Sometimes capacitors from three years to
about 18 months ago can fail but still look ok. Usually they'll bulge
though, not always. I've had this problem more than once. It only takes one
cap to cause problems.

 

[Russell]

Sorry, meant to say:
"I recommend an Antec, Enermax or Seasonic at 400W or higher"

 

[DaveW]

My wild guess, which it is, is that you have a single component on the
motherboard (capacitor, chip, etc), which you haven't tried switching out
apparently, with a thermal fault that occurs over time during operation. I
think your next step is to replace the board.

 

[kony]

Including mobo? I still think you need to study the capacitors, maybe test
them.

.... but he's tried two different motherboards

 

[Trent©]

Problem: Spontaneous power-offs that take place between 15 seconds and 30
minutes after booting. As if the power cord was yanked out of the back.
Green M/B LED remains on, power cord has to be disconnected for several
seconds before re-boot can take place.

1. Boot to a DOS system disk. Let the machine run for a legitimate
period of time.

2. My guess would be the mainboards. Try a different
board...different manufacturer.


Have a nice week...

Trent

Follow Joan Rivers' example --- get pre-embalmed!

 

[Nick G]

i am currently using the brand new a7v8x and can see no bulging...

 

[~misfit~]

... but he's tried two different motherboards

<G> Yeah, I missed that bit in this extensive thread. That's why I asked
"Including mobo?"

 

[~misfit~]

i am currently using the brand new a7v8x and can see no bulging...

Yeah. Sorry Nick, I missed that bit. <G> I guess I should read fewer
newsgroups and read the ones I continue with more thouroughly.

Good luck with your interesting problem. A great opportunity to learn.

 

[Manny]

The following problem has confounded every IT friend
and support person i have presented it to and appears
to defy logic

Spontaneous power-offs that take place between 15 seconds
and 30 minutes after booting.

home-built 18 months ago, ran fine until last week.
I have been building PCs for 15 years

Asus a7v333 latest bios
Asus a7v8x-x v06 bios - rejects flash to latest 08 bios

Radeon 9800pro - exhibits power-down symptoms every time
Radeon 9700 Pro exhibits power-down symptoms every time,
GeForce Ti4600 - exhibits power-down symptoms every time,

300W unbranded, came with case
400W high quality, multi-fan
the 400w PSU is made by Q-Tec and

What did you learn in your 15 years of building PCs?
You should have measured voltages, lightened the load
(not by swapping one power hog of a video card for
another), and tried a high quality power supply.

Those motherboards rely on +3.3V and +5V almost
exclusively, and combined with a high-power video card,
many power supplies just can't handle the load. It's
possible that your 300W was marginal but weakened as its
capacitors aged, and the Q-tec may have been inadequate
all along. Anyone with 15 years of experience building
PCs should have noticed instantly that the Q-tec was
crap by simply peeking through the vent holes and seeing
all the empty space and small heatsinks and transformer.
Borrow, buy, or steal a good supply, like an Antec
(AKA Channel Well, but only if its +3.3V is rated for
at least 20A and its +12V for at least 15A), Fortron
(many names, like Sparkle, Aopen), or something used
by a major computer manufacturer, except Dell (wires
mixed up, will destroy motherboard when plugged in).

 

[Manny]

Wild guess - something is putting spikes on a power line and
triggering a crow-bar shutdown. At least it fits the facts.

Not even with the Q-tec crap supply. Even it has an RF filter
that'll block almost all spikes.

Name one consumer grade ATX supply made in the past 10 years
with a crowbar circuit in it. All they have is shutdown,
and it doesn't trigger on spikes, except unintentionally.

 

[Trent©]

yes, but only in windows or during the install. it has yet to power off
whilst in the bios

Then you've SOLVED the problem!!!

You just need to find out what culprit is the villain. lol

Good luck.


Have a nice week...

Trent

Follow Joan Rivers' example --- get pre-embalmed!

 

[Trent©]

It was tested in two different properties in different parts of London and
on multiple mains sockets. I am writing this in one of those properties and
on a working laptop which is being mains powered with no problems. The most
bizarre thing about this problem is that i have replaced every single major
component at least once if not twice and have still got the problem!

I'm reading down thru the threads...so there may be more important
stuff down near the bottom...but, here's what I got from you so far...

You don't get the problem if you boot into the BIOS...with nothing
else installed.

So...you now know...

Mainboard is good at this level.

Memory is good at this level.

Video card is good at this level.

CPU and fan are working good at this level.

Mouse and keyboard (?) are working good at this level.

Now...add a Windows 98 hard drive. Run that for a while.


Have a nice week...

Trent

Follow Joan Rivers' example --- get pre-embalmed!

 

[Trent©]

... but he's tried two different motherboards

Exactly.

And the boards work fine...and so does everything else...when just
sitting in the BIOS.


Have a nice week...

Trent

Follow Joan Rivers' example --- get pre-embalmed!

 

[Jonathan Starr]

Hi, I have had a look through this thread but no one seems to have
mentioned the CMOS battery.

I had a brand new motherboard that had these exact symptoms, I tried
everything but nothing made a difference not even buying a top of the
range 'PC power and cooling' power supply rated for huge servers.

I was so sure it was a power issue that I didn't bother checking the
CMOS battery, it was brand new motherboard so the battery had to be
fine...

Sure enough the battery was low (but not that low) and replacing it
cured the problem completely just like that.

It was a co-worker that suggested changing it BTW, I probably would
have never even checked it left to myself and would have probably sent
the board back.

It doesn't seem to be an uncommon problem either after asking people I
know, although most motherboards just forget their settings at every
boot rather than just re-setting randomly.

Best of luck with it,

-Jon

 

[Jay Cousins]

The following problem has confounded every IT friend and support person i
have presented it to and appears to defy logic so i am throwing it to a
broader audience of experts to see if it elicits some ideas. Thanks in
advance for considering it and apologies for cross-group posting!

Problem: Spontaneous power-offs that take place between 15 seconds and 30
minutes after booting. As if the power cord was yanked out of the back.
Green M/B LED remains on, power cord has to be disconnected for several
seconds before re-boot can take place.

PC background: home-built 18 months ago, ran fine until last week. I have
been building PCs for 15 years and have spent the last week running through
every permutation of test i can think of, to no avail.

Hey, Jay here. There is one component of the computer that you did
not replace and has to be constant the whole time. Even if you take
the MB out of the case you still have to plug up the POWER SWITCH to
it. If the power switch is flaky then you can lose power suddenly,
reboot, and cause hard crashes. On just about all PSUs if you just
kill the power like that with a short in a wire you will either have
to unplug the cord or reset the PSU(hold down the power button while
flipping the switch on the back to the - sign). Try replacing the
whole CASE with a brand new Antec PSU and see what happens.