ending up in bios

  • Thread starter Thread starter Linea Recta
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L

Linea Recta

I recently replaced the coin cell on my mainboard because, when booting the
PC, I often ended up in the bios setup. For some time things were OK, but
now and then I'm having the same symptom again.
Would this coin cell (5 euro!) be exhausted again?!



--
regards,

|\ /|
| \/ |@rk
\../
\/os
 
Linea said:
I recently replaced the coin cell on my mainboard because, when booting the
PC, I often ended up in the bios setup. For some time things were OK, but
now and then I'm having the same symptom again.
Would this coin cell (5 euro!) be exhausted again?!
Click to expand...

You can measure the voltage on the coin cell, while it is in circuit.

To do so, connect the black lead of the multimeter to some shiny metal
on the case. I use an alligator clip and clip the meter lead to an
I/O screw in the I/O area on the back of the computer. The benefit
of doing this, is only having to handle the red meter probe while
making readings.

Set the meter to "volts" and make sure to use the pair of holes
on the meter intended for "volts/ohms" readings. The nice shiny
surface of the cell, with the "+" on it, makes an easy target
to touch with the red multimeter probe. So you don't need to remove
the battery to check it.

The CMOS coin cell (CR2032) should be 3.0V when new. Below about
2.4V, the board won't be getting enough voltage to guarantee correct
CMOS settings storage or RTC clock operation. Replace the battery
if it is below 2.4V. The "knee" of the discharge curve is sharp
enough, that in a matter of days, it'll be at a much lower voltage.
So once it decides its time is up, it will relatively rapidly
discharge towards zero.

The CR2032 could last anywhere from 3 years to the shelf life of
the battery (10 years?) depending on the user's computer usage
pattern. Switching off the power supply at the back, after each
working day, heads you in the "3 year life" direction.

The computer does not charge that battery. Neither should you try
to charge it. The CR2032 is not designed to be charged.

Paul
 
Linea said:
I recently replaced the coin cell on my mainboard because, when booting the
PC, I often ended up in the bios setup. For some time things were OK, but
now and then I'm having the same symptom again.
Would this coin cell (5 euro!) be exhausted again?!
Click to expand...

It's possible that you put in a weak new battery. More likely is that you
did not reset the BIOS after replacing the battery, especially when you did
so to replace a dead or weak battery (i.e., you waited until you had to
replace the battery, not by replacing it before it was needed).

The BIOS in EEPROM gets copied into CMOS. The battery keeps alive the CMOS
copy. If the battery gets too weak, it is possible the settings get
corrupted in the CMOS copy. You put in a new battery but that merely
provides the power to keep alive whatever settings are currently in the CMOS
table. If the settings are wrong, they'll still be wrong after you put in a
new battery.

Record any modified settings in the BIOS. Replace the battery. Reset the
BIOS (how depends on what you have which was never mentioned). This copies
the hard copy of the settings from the EEPROM for the BIOS into the CMOS
table. Then re-input your modified settings (there are some utilities to
save the BIOS settings but often that takes more work than just recording
the few that you changed and restoring them after the CMOS reset).
 
VanguardLH said:
It's possible that you put in a weak new battery. More likely is that you
did not reset the BIOS after replacing the battery, especially when you
did
so to replace a dead or weak battery (i.e., you waited until you had to
replace the battery, not by replacing it before it was needed).
Click to expand...


Your reply might be relevant in this case. Indeed, I have not reset the
bios.
I remember the wrapping of the battery had a date of several years in
future.
However, I have to point out that the flaw is incidental...


The BIOS in EEPROM gets copied into CMOS. The battery keeps alive the
CMOS
copy. If the battery gets too weak, it is possible the settings get
corrupted in the CMOS copy. You put in a new battery but that merely
provides the power to keep alive whatever settings are currently in the
CMOS
table. If the settings are wrong, they'll still be wrong after you put in
a
new battery.

Record any modified settings in the BIOS. Replace the battery. Reset the
BIOS (how depends on what you have which was never mentioned). This
copies
the hard copy of the settings from the EEPROM for the BIOS into the CMOS
table. Then re-input your modified settings (there are some utilities to
save the BIOS settings but often that takes more work than just recording
the few that you changed and restoring them after the CMOS reset).
Click to expand...


I'll give it a try.
Thanks for the explanation.



--
regards,

|\ /|
| \/ |@rk
\../
\/os
 
VanguardLH said:
It's possible that you put in a weak new battery.
Click to expand...

This is rare but it happens . . . to me at least once, viz. a CR2032
CMOS battery failing within 3 to 6 months of replacement. They
usually last 3 or 4 years.
 
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