This problem has baffled everyone...

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

http://www.motherboardrepair.com/

"Nick G" ignore @ nospam.com wrote in message
...
Bad Caps.
Can you expand on this?
thks
n

thanks. caps on both boards look fine. no leaks or discolouration.
"BigStan" wrote in message
...
He means bad capacitors. Sometimes they go south and cause instability.
Link
here -

http://www.motherboardrepair.com/

"Nick G" ignore @ nospam.com wrote in message
...
Bad Caps.
Can you expand on this?
thks
n

"Nick G" ignore @ nospam.com wrote in message ...
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.
--
Mantric

Nick G wrote:
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.
--
~misfit~

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

"Mantric" wrote in message
...

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.
--
Mantric

Nick G wrote:
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.
--
~misfit~

"BigStan" wrote in message
...
He means bad capacitors. Sometimes they go south and cause
instability. Link here -

http://www.motherboardrepair.com/

"Nick G" ignore @ nospam.com wrote in message
...
Bad Caps.
Can you expand on this?
thks
n

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

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.

--
DaveW



"Nick G" ignore @ nospam.com wrote in message
...
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.

Components tested (all of which have, in every configuration, replicated
the
problem):

M/B
Asus a7v333 latest bios
Asus a7v8x-x v06 bios - rejects flash to latest 08 bios
temp problem? No. M/B temp under 35 degrees c at time of power-down (have
been staring at PC probe's temp montitor as it has gone down on 2
occasions.
Immediate boot-ups after power-down reveal no discrepancies in bios-based
temp monitor i.e. also reports 35 degrees c or under)

CPU
AMD Athlon 2100+
AMD Athlon 2500+
temp problem? No CPU temp under 40 degrees c at time of power-down (have
been staring at PC probe's temp montitor as it has gone down on 2
occasions.
Immediate boot-ups after power-down reveal no discrepancies in bios-based
temp monitor i.e. also reports 40 degrees c or under). Bios-based
auto-shutdown set at 95 degrees c

HD
8GB Seagate- freshly fdisked/formatted but fails to complete winXp install
(lasts between 15mins and 25 mins) before powering off
20GB IBM- Win98SE - exhibits power-down symptoms every time, works fine on
other machines. Lasts the longest time, up to 30 mins, running in 640x480
res
80GB Maxtor - Win Xp Home - lasts the shortest time, rarely more than 15
minutes, power-offs can happen without any apps running but tends to
happen
within a few seconds of 3Dmark03 running and within 15 minutes of Norton
AV2K4 running
Software problem? No. problem replicated with winxp install on fresh disk.
Also run each HD in isolation to others, i.e. with no other no HD
IDE/power
connections

Graphics
Radeon 9800pro - exhibits power-down symptoms every time, works fine on
other machines
Radeon 9700 Pro exhibits power-down symptoms every time, works fine on
other
machines
GeForce Ti4600 - exhibits power-down symptoms every time, works fine on
other machines
Graphics card problem? maybe, but three different cards have replicated
the
problem. Run with default VGA drivers and latest drivers

Memory
512Mb PC2700 Apacer CL2.5
512MB PC3200 Infineon CL 2.5
Memory problem? maybe, replicated with both DIMMS though. Could it be a
voltage issue? everything set to default in bios and no voltage setting
tampered with at any stage.

PSU
300W unbranded, came with case
400W high quality, multi-fan
Power problem? Dont know. the brand new 400w PSU immediately replicated
the
problem. Have tried 4 different power cords in two houses on 5 different
sockets (!). All replicated the problem.

Others:
case - generic, have tried running the pc out of the case without any case
jumper connections or any other connections other than PSU housing, using
screwdriver to boot.
CD, DVD, Floppy, Soundcard, USB expansion card, game card expansion, other
USB connections - taken out/disonnected (ide, power etc) but problem still
exists
I have even tried, once an app is running, diconnecting mouse, keyboard
and
monitor (!!) with the problem still taking place.

I have effectively changed PC entirely with these tests and still get this
problem!

One idea that was thrown out was a bios-residing virus. is there such a
thing (i cannot find mention of one anywhere let alone scanning or removal
methods)?

Does anyone have any other ideas?

Any help very much appreciated

Nick
ps Please post reply (e-mail address is false)

On Wed, 11 Feb 2004 12:43:21 +1300, "~misfit~"
wrote:

Nick G wrote:
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.

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

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

"~misfit~" wrote in message
news
Nick G wrote:
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.
--
~misfit~

"BigStan" wrote in message
...
He means bad capacitors. Sometimes they go south and cause
instability. Link here -

http://www.motherboardrepair.com/

"Nick G" ignore @ nospam.com wrote in message
...
Bad Caps.
Can you expand on this?
thks
n