Motherboard keeps giving checksum error after installing new battery

Question

I am repairing a computer with an ASUS M2NBP-VM CSM ACPI motherboard (I am not sure this is the correct description of the motherboard but, at least, this is what gets printed to the screen during boot).

During boot, I get the following error message:

CMOS checksum error - Defaults loaded

Indeed, the time, date, and boot device priority are reset and the values I had set up before switching the computer off are gone.

My first explanation was that the CMOS battery must be empty so I bought and installed a new one. But the behaviour has not changed: after switching off and disconnecting the power cable, the next time I switch on, the CMOS settings are lost and the error message is printed again.

Any suggestions as to what I should check next?

EDIT

Following the suggestions contained in the answers and comments, I performed a few further tests using another computer that I know is working properly, i.e. it does not lose BIOS settings between reboots.

1. Unplugged computer with its own battery on, waited a minute or two, plugged again, booted: settings are there.
2. Unplugged again, removed battery, put new battery (the one I had used to test the bad computer as described above) in, plugged in, booted, set up time and date, shut down, unplugged, waited for a few minutes, plugged, booted: settings are there. So: the new battery is good.
3. Unplugged again, removed new battery, put old battery from bad computer in, plugged, set up time and date, shut down, unplugged, waited for a few minutes, plugged, booted: settings are NOT THERE. So: the old battery is bad.

So, I have ruled out the case that the new battery is bad. I have performed another test on another computer I am trying to repair. Same model as the bad one above. Removed battery and put the new battery in: it does not retain the settings. The reset jumper is also in the proper position (no reset).

So the problem must be in the main boards. Since I would find it unlikely that they have both broken in the same way, I guess the only test left is to flash the firmware on the main board. Only, I do not understand why this should work: the old firmware has worked before, why should the old firmware have stopped working at some point?

Answer 1

Even though it may sound obvious, I will add this answer in case someone in the future needs help.

Be sure the new battery is making good contact on both poles. I went thru several rounds of contact cleaning and pin bending/unbending until it finally worked for me. Even if the battery holder seems to keep the battery firm in place, the connectors might need some extra help depending on their age and how the motherboard is oriented (vertically or horizontally) when in use.

Some people try more extreme solutions like soldering an extra wire to bypass whatever is not working well on the motherboard (there are videos about this on YouTube), hopefully you will not need to do this.

Answer 2

If you've confirmed the new CMOS battery is outputting the expected voltage, then more than likely it's not your problem.

Next steps:

• Reset the BIOS to defaults (option in the BIOS), save and reboot.
• If that doesn't work, try (re)flashing the BIOS with the latest version offered by the Motherboard manufacturer (Asus).
• If that doesn't help, replace the motherboard.

Answer 3

1. Are you setting and saving the settings?
2. Is the new battery good?
3. There is usually a CMOS jumper for resetting. Is it possible it fell out or was placed on the wrong pins?