computer components & hardware - CMOS setting reset itself after cold boot

cpliu wrote:
This P4/Asus P4P800 DELUXE system works fine for a while. It's my
secondary system so I don't use it often. Lately it has the following
message when booting cold:

CMOS setting wrong
CMOS Date/Time nto set
New CPU installed. Please enter setup to configure your system.
Press F1 to run setup.
Press F2 to load default values and continue.

The date would become January 1 2002. I have to set the time. After
reboot, it remembers the setting and the message does not show up. If
I turn it off for a while, then it always reset itself.

What is the cause of this problem? How can I fix it?

Thanks for the information.

liu

Change the CMOS coin cell. It fits into a socket on the motherboard.
Note the orientation and put the new one into the socket the same
way as the original.

http://data.energizer.com/PDFs/cr2032.pdf

The CMOS battery is only used, when the computer is switched off or
unplugged. Thus, if you put a computer in storage in your closet,
the battery will be under a slight load (measured in microamps).
If you know a computer will not be used for a long long time, you
might consider recording the BIOS settings, and then removing the
battery from its socket, so it doesn't drain. Then put the battery
back before plugging the computer into the wall again. (Affix battery
to chassis as a reminder to put it back.)

As long as the +5VSB is running on the motherboard (signified by
the green LED on the Asus motherboard glowing), the CMOS battery
is not being used. When the battery is not being used, it will
last for whatever period that is the shelf life for that type
of battery (could be 10 years or less).

The last fresh battery I checked, read a bit more than 3.0 volts.
If you connect a multimeter to the top of the battery, and connect
the ground on your meter to the computer chassis, a reading of
less than 2.4V means it is time to change the battery. The
Southbridge typically needs 2.0V and there is a Schottky diode in the
path that wastes another 0.4V, so that is where the 2.4V
end-of-life value comes from. When a Southbridge has a publicly
available datasheet, you can actually look up the minimum CMOS
voltage for it. Each chipset could be slightly different, and
the end of life value could be different as well. The 2.4V
number is an approximate value.

Paul