Checksum error after battery replacement

  • Thread starter Thread starter knack
  • Start date Start date
K

knack

After replacing the battery of the ASUS SP97-V mainboard with a newly
purchased battery from Wal-Mart, I continue to get a checksum error during
POST. The error seems to occur after the power has been shutdown completely.
However, if the PC is restarted immediately, then it will usually not
exhibit the problem.

Is the power supply supposed to provide a recharging function?
Should I install another new battery?
Is there something wrong with the mainboard's CMOS?
 
"knack" said:
After replacing the battery of the ASUS SP97-V mainboard with a newly
purchased battery from Wal-Mart, I continue to get a checksum error during
POST. The error seems to occur after the power has been shutdown completely.
However, if the PC is restarted immediately, then it will usually not
exhibit the problem.

Is the power supply supposed to provide a recharging function?
Should I install another new battery?
Is there something wrong with the mainboard's CMOS?
Click to expand...

The power supply should never charge the CMOS coin cell, because
it could explode. There is a dual diode, a device with three legs,
usually near the CMOS coin cell, and it prevents the back flow
of current into the battery. Either +5VSB or the coin cell, power
the CMOS well on the Southbridge. The "well" is a section of silicon
which is separately powered from the rest of the chip, and special
design techniques have to be used for the logic signals inside
the "well", to be accessable to the rest of the chip. For example,
when the computer reads out the battery backed real time clock, that
data crosses the boundary inside the Southbridge.

The spec on a typical Southbridge is the "well" runs on from
about 3V down to 2V. Allowing for some voltage drop across the
diode, that means the battery should have about 2.4V minimum,
to keep the clock running and the CMOS valid. (I'm assuming
a 0.4V drop across the dual diode, at low current.)

Have you tried refreshing the settings ? Write down all your
custom settings in the BIOS, and then do a "Load Setup Defaults"
from the Exit menu. See if that makes the CMOS happy. Clearing
the CMOS is effectively what you did when you changed the battery,
so I cannot see repeating that doing anything positive.

About the only other thing that comes to mind, is maybe the dual
diode is damaged. Asus leaves a ticking time bomb in many motherboards,
in the form of the dual diode. If you do a "clear CMOS" operation,
without unplugging the computer, or at least turning off the supply
so the green LED stops glowing, the computer can be damaged when
you use the CLRTC jumper. If the green LED is glowing, then the
CLRTC jumper shorts +5VSB to ground, through the dual diode. The
dual diode can actually get burnt to the point that the tiny lettering
on it can no longer be read. Once the dual diode is damaged, then
the CMOS well generally no longer get the power it needs. In that
case, you would probably no longer have a working clock between
power off events.

HTH,
Paul
 
Paul said:
The power supply should never charge the CMOS coin cell, because
it could explode. There is a dual diode, a device with three legs,
usually near the CMOS coin cell, and it prevents the back flow
of current into the battery. Either +5VSB or the coin cell, power
the CMOS well on the Southbridge. The "well" is a section of silicon
which is separately powered from the rest of the chip, and special
design techniques have to be used for the logic signals inside
the "well", to be accessable to the rest of the chip. For example,
when the computer reads out the battery backed real time clock, that
data crosses the boundary inside the Southbridge.

The spec on a typical Southbridge is the "well" runs on from
about 3V down to 2V. Allowing for some voltage drop across the
diode, that means the battery should have about 2.4V minimum,
to keep the clock running and the CMOS valid. (I'm assuming
a 0.4V drop across the dual diode, at low current.)

Have you tried refreshing the settings ? Write down all your
custom settings in the BIOS, and then do a "Load Setup Defaults"
from the Exit menu. See if that makes the CMOS happy. Clearing
the CMOS is effectively what you did when you changed the battery,
so I cannot see repeating that doing anything positive.

About the only other thing that comes to mind, is maybe the dual
diode is damaged. Asus leaves a ticking time bomb in many motherboards,
in the form of the dual diode. If you do a "clear CMOS" operation,
without unplugging the computer, or at least turning off the supply
so the green LED stops glowing, the computer can be damaged when
you use the CLRTC jumper. If the green LED is glowing, then the
CLRTC jumper shorts +5VSB to ground, through the dual diode. The
dual diode can actually get burnt to the point that the tiny lettering
on it can no longer be read. Once the dual diode is damaged, then
the CMOS well generally no longer get the power it needs. In that
case, you would probably no longer have a working clock between
power off events.

HTH,
Paul
Click to expand...

Thanks, Paul, for all that very unusual knowledge. I saved it to a Notepad
file.

Whenever I open the cabinet I unplug the power cord. So, yes, the power
supply was deenergized when I changed the battery.

I've had my custom BIOS settings penciled into the mainboard's manual for
several years. I haven't made any changes there since 2000.

I forgot to mention that whenever the checksum error appears, my custom BIOS
settings become lost, so then I must spend 10 minutes reentering the BIOS
settings in order to boot the computer. It never occurred to me to load the
BIOS default settings as you suggested, because if I did my IRQ-jumpered ISA
slot modem will not work. WinNT4 is not plug and play, so I must configure
the modem and set the BIOS to dedicate IRQ-11 to ISA.

This morning the PC started up normally, but if I get the checksum error
again tomorrow, I'll load the BIOS defaults as an experiment.
 
knack said:
After replacing the battery of the ASUS SP97-V mainboard with a newly
purchased battery from Wal-Mart, I continue to get a checksum error
Click to expand...

Did you measure the voltage of the new battery?
Perhaps the battery is too old, or of the wrong type (Ag or Mn instead
of Li).

Tom
 
Did you measure the voltage of the new battery?
Perhaps the battery is too old, or of the wrong type (Ag or Mn instead
of Li).
Click to expand...

To the OP: are you getting a CMOS Checksum Error - or a BIOS Checksum Error?
If the former, verify the battery is putting out roughly 3V. Then, if you can
get into the CMOS Setup Utility, try the "set defaults" operation. If that
doesn't help, try manually clearing the CMOS (read the user's manual for the
procedure).

If the latter, the battery has no bearing on the flash rom contents...
 
Paul said:
The power supply should never charge the CMOS coin cell, because
it could explode. There is a dual diode, a device with three legs,
usually near the CMOS coin cell, and it prevents the back flow
of current into the battery. Either +5VSB or the coin cell, power
the CMOS well on the Southbridge. The "well" is a section of silicon
which is separately powered from the rest of the chip, and special
design techniques have to be used for the logic signals inside
the "well", to be accessable to the rest of the chip. For example,
when the computer reads out the battery backed real time clock, that
data crosses the boundary inside the Southbridge.

The spec on a typical Southbridge is the "well" runs on from
about 3V down to 2V. Allowing for some voltage drop across the
diode, that means the battery should have about 2.4V minimum,
to keep the clock running and the CMOS valid. (I'm assuming
a 0.4V drop across the dual diode, at low current.)

Have you tried refreshing the settings ? Write down all your
custom settings in the BIOS, and then do a "Load Setup Defaults"
from the Exit menu. See if that makes the CMOS happy. Clearing
the CMOS is effectively what you did when you changed the battery,
so I cannot see repeating that doing anything positive.

About the only other thing that comes to mind, is maybe the dual
diode is damaged. Asus leaves a ticking time bomb in many motherboards,
in the form of the dual diode. If you do a "clear CMOS" operation,
without unplugging the computer, or at least turning off the supply
so the green LED stops glowing, the computer can be damaged when
you use the CLRTC jumper. If the green LED is glowing, then the
CLRTC jumper shorts +5VSB to ground, through the dual diode. The
dual diode can actually get burnt to the point that the tiny lettering
on it can no longer be read. Once the dual diode is damaged, then
the CMOS well generally no longer get the power it needs. In that
case, you would probably no longer have a working clock between
power off events.

HTH,
Paul
Click to expand...

The new replacement battery (Energizer CR2032, from Wal-Mart) turned out to
be defective (poorly charged). So I got another new battery (Energizer 2032,
from K-Mart) and replaced the one that continued to result in the error...
no more problem!
 
Back
Top