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Joe J 06-04-2011 08:41 PM

CMOS checksum error
 
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.


Paul 06-04-2011 10:21 PM

Re: CMOS checksum error
 
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

VanguardLH 06-05-2011 03:12 AM

Re: CMOS checksum error
 
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.


"6 month old" doesn't say that you got it new or used. It doesn't say
how long from motherboard manufacturer, storage, shipping, more storage
at reseller, shipping to retailer, more storage, and then you get it. 6
months for you could be years for the motherboard and CMOS battery.

Don't know how old you are but it's likely that you have seen brand new
batteries die before a reasonable expiration in their use. Nothing is
perfectly constructed when mass produced.

What do you have to lose? I've seen a set of 5 batteries (CR2032) sold
on eBay for under $5. That's damn cheap (and far cheaper than getting
them from Best Buy or Radio Shack). Just be sure to ask the eBay seller
what is the expiration date for the batteries. If they don't tell you
for whatever excuse they come up, don't buy them. They might already be
expired so they won't have much life before they start to go dead.

Joe J 06-06-2011 03:34 PM

Re: CMOS checksum error
 

"Paul" <nospam@needed.com> wrote in message
news:iseb64$qrn$1@dont-email.me...
> 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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