Ami bios problem

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I have a WinXP machine with an MSI 875P series motherboard, and Ami
BIOS. The computer has been running perfectly happily for about 18
months with no problems.

It's developed a problem with the BIOS over the last few days that's
baffled me.

The symptoms are as follows:

On power on (from cold) the BIOS logo screen comes up, and the BIOS
announces the CMOS is corrupt.

I've checked the battery, and it seems fine. I out a new one in anyway,
after first disconnecting the AC and leaving the CMOS reset jumper set
to ground the CMOS for about an hour.

On booting I loaded the BIOS defaults and entered the same settings it's
always had (and that have worked fine until now - I'm not overclocking
by the way). PC booted OK.

Later same day PC had gone to standby mode (S3) and on trying to wake it
up it failed to load Windows or give a screen display. I rebooted.
Corrupt BIOS.

Re-enter settings, warm reboot, all OK - but still refusing to wake from
standby, and on rebooting from standby - corrupt CMOS.

On checking the BIOS settings I found that the clock is running OK even
after the PC's been switched off overnight - and if I set it to shadow
the BIOS in RAM it starts to boot then halts before the screen display
is set, then repeatedly tries to boot. Clear the BIOS and it's fine
until either standby or power off and it corrupts again.

It seems to be retaining some settings even after power-off (clock,
shadow BIOS to RAM) and will warm reboot fine after I've configured the
BIOS - but a cold reboot/standby results in it losing settings.

I'm pretty sure  can rule out the PSU, CPU, RAM and just about
everything else, as once it's up and running it works fine - it boots
fine once the BIOS has been reconfigured, and there's been no recent
hardware changes.

Any ideas?
Tim Willets

Re: Ami bios problem

On Wed, 29 Mar 2006 17:02:28 +0100, Tim Willets

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Since you have not had to reflash the bios, it is still
stored intact in the EEPROM, what *appears to be*  happening
is the system itself is too instable to decompress or run it
at boot-time.   That it is bios is somewhat coincidental in
that it is just the first thing the PC is trying to do in
it's instable state.

If the system had been allowed to sit long enough that there
was significant change in it's temp, it had cooled over
several minutes, it could possibly be a mechanical
connection problem or a manufacturing flaw (such as poor
solder joints) or damage like a (possibly near invisible)
crack in a board that becomes intermittent after a while.
This seems unlikely but a marginally working part can later
fail from such problems too, it's not "always" evidence a
board was manufactured or handled perfectly simply because
it works initially.

I would tend to suspect it is instead the capacitors, either
on the board or in the power supply and they are degraded
onto the point where when cold their function is degraded
(as it always will be, but now degraded below a stability
threshold) or they have actually hit a more obvious failure
threshold such as venting, which would be visibly obvious
(examine the board capacitors and unplug the PSU from AC
then inspect it as well.

Re: Ami bios problem

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On a close look, there's signs of venting on a PSU cap (I've a 30+ year
old Marshall guitar amp so I know what venting capacitors look like).
Problem solved (I hope). Many thanks.
Tim Willets

Re: Ami bios problem

On Thu, 30 Mar 2006 23:50:30 +0100, Tim Willets

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Out of curiosity, what make and model power supply was it?

If this is the only failure point, it might be viable to
replace that (probably 12V rail cap) and the corresponding
5V rail caps.  About $1 each at major electronics houses
such as Digikey, preferribly a very low ESR part such as
Panasonic FM or Nichicon HE series in at least same voltage
rating and same (or better, higher) uF, so long as it
physically fits in the alotted space.  IE- many PSU are
limited to 10 or 12mm diameter but tallest available.

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