"Paul" <> wrote in message
news:iseb64$qrn$...
> Joe J wrote:
>> 6 month old Acer desktop and starting today when it shuts down and
>> restarts, it comes up with the Bios screen and an error reading CMOS
>> checksum error. If I escape it will reboot into Win7. Goggling, it talks
>> about this error being caused by a bad battery. Is that likely after
>> only 6 months? My other two desktops have been running for 6 and 8 years
>> w/o changing.
>> Any other ideas. Case has never been opened.
>
> There are enough amp-hours in a CR2032 to power the clock and CMOS RAM
> for 3 years (with the computer turned off and unplugged). I have a few
> computers
> here which remain un-powered, and the calculated value agrees pretty well
> with the observed time period.
>
> If the computer remains in standby suspend to RAM (power supply still
> switched
> on at the back and +5VSB available), then the battery isn't used at all.
> The
> shelf life of the battery is around 10 years in ideal conditions, and if
> the
> computer remains powered all the time (stays in Suspend to RAM when not
> being used), then you'd expect to see ten years.
>
> I've purchased "flat" batteries at the mall, so it happens. You can get
> defective ones. That is less likely with a brand name (that happens
> to not be a counterfeit).
>
> Leaving the "Clear CMOS" jumper in the wrong position for too long, can
> drain the battery. Accidental contact with some battery circuit, might
> also drain it. There have been defective motherboards, where the battery
> drained faster than it should, implying there is something connected
> to the circuit that shouldn't be there.
>
> Using a multimeter, you should see a bit more than 3.0V on the battery.
> You can measure the battery, without removing it from the socket. Clip
> the multimeter ground onto a chassis screw (like in the I/O plate area),
> then touch the (+) terminal on the battery with the red test lead on
> the meter. Make a volts reading, and verify the value.
>
> If you don't own a multimeter, my local RadioShack used to have a battery
> tester at the counter, and you could take a reading there. That would
> require popping out the battery, then driving to the mall.
>
> The CMOS is good to 2.0V roughly. Since there is a Schottky dual diode
> in the path, that drops another 0.3V or so. At the battery, that means
> 2.3-2.4V is as low as the battery can reasonably go, before it is getting
> too low.
> The "knee" on a CR2032 is pretty sharp. Once the battery voltage starts to
> dip, the battery may provide the 10uA operating current for another three
> weeks,
> before it's entirely flat.
>
> A gratifying second symptom, would be the RTC clock being reset to its
> origin value, every time you switch off the computer completely. Then
> you know for sure, the battery is at fault. If time keeping is still
> perfect,
> but you're getting reports of a CMOS checksum error, then you'd be a
> little
> less certain you'd nailed it. It's certainly possible, that the RTC
> oscillator
> will run at a lower voltage, than is required to run the CMOS RAM, so
> seeing
> something like that happen isn't impossible. But if you wait a week or two
> (with
> the PC switched off at the back), you'd hope to see the CMOS clock also
> foul
> up when the power is switched off.
>
> The CMOS RAM is a portion of the Southbridge chip on the motherboard.
> There have
> been cases, where the CMOS is temperature sensitive, or there is a defect
> which
> causes less than ideal storage characteristics. On one chipset, I got the
> impression they were cheating, and to shore up the defective silicon, they
> were writing the CMOS values into EEPROM instead. If the computer was in
> an extremely cold room, that might have something to do with it. But it's
> been a while since I've seen hints, that a Southbridge design was broken.
>
> Some users, who are outside the warranty period, and find themselves going
> through one battery after another, sometimes use a larger battery in a
> holder,
> and connect that in place of the coin cell. That may be cheaper, if the
> discharge rate is way out of line.
>
> 1) Replace the battery. If all is well, you might see a long life on the
> replacement. If you leave the switch on, at the back of the computer,
> the
> battery may last even longer than 3 years (the expected runtime if the
> computer was in storage).
>
> 2) If the second battery goes flat too, try to contact Acer before the
> warranty expires. If it's a motherboard issue, consider how many
> dollars
> per year the problem is costing you, before doing something more
> drastic. If you're replacing them every two weeks, then it's time
> for some warranty work.
>
> When you buy the battery, buy it from a "high traffic" source. If the
> battery has a "best before" date, that can help you determine whether
> they're fresh stock.
>
> 3) If you have a multimeter, you can also check the battery, to confirm it
> is
> defective. You can use the services of RadioShack or equivalent, to
> verify
> the condition of the battery. Note that the motherboard is not allowed
> to
> "charge" the coin cell, and the leakage spec is around 1 microamp. If
> more than 1 microamp flows continuously into the battery, gas pressure
> may
> build up. They've set the battery up on purpose, so it won't get
> charged.
>
> 4) If you're seeing reports of corruption, and the battery still reads
> approx
> 3V, then you know it's warranty time.
>
> Paul
Paul, thank you for that very comprehensive answer!
Who said newsgroups are dead.
Joe
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