CMOS battery failure

san_kvs February 1, 2009 at 04:15:14
Specs: Windows Vista
Hi everyone,
Actually my PC is only six months old and has been running with no problem, but two days before when i switched on the UPS then suddenly one or two seconds the CPU automatically turned on and off,,,then i as usual turned the cpu on and i got an error message like CMOS battery failure and i had to change data and time, then aftewards it happens once in a while and i've noted that this error message only occurs when the aforementioned UPS behavior happens..i am totally confused whether its CMOS battery problem or UPS problem, plz help me guys:)))

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February 1, 2009 at 05:46:46
For a start it is not a CPU, it is a computer. The CPU is a single chip on the motherboard. The largest one there with a fan and a heat-sink on it.

It is not unusual for a computer to come on then turn of when power is first applied. There are settings in the BIOS that will prevent this but its not a problem.

The CMOS battery failure is something you can fix very easily. The CMOS battery is a small coin battery on the motherboard that retains settings like time and date in the CMOS memory when the computer is shut down.

The fact that it only happens when the UPS is turned on is to be expected as modern PC delivers a small amount of power to the motherboard even when they are switched off. It is this small amount of power that is retaining the settings in the CMOS memory.

The only way to remove all power to the computer is to remove the power cord or turn the UPS off. That is when the CMOS memory loses its contents.

The solution is to replace the CMOS battery and all the problems should disappear. The battery is cheap and can be got for any computer shop of photographic shop. The same type of battery is often used in cameras.


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February 2, 2009 at 04:58:59
Thanks man, i dont know anything about these kinds of stuffs and ur comment was really helpful, i will change it as soon as possible

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February 3, 2009 at 11:50:24
Hi there san_kvs

I recently had a similar problem with a new motherboard that worked fine for about 2 months then suddenly started giving an error at startup:
and losing its settings and time. I replaced the battery taking extra care to ensure it was properly seated, but all to no avail. I started keeping the power supplied all the time (with the machine switched off), which allowed the PSU to trickle power to the CMOS so it didn't lose its memory.

In the end I contacted ASUS, who agreed that is probably faulty motherboard and I have returned it through the vendor.

Good luck


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