I recently repaired an IBM Thinkpad R31 Laptop with an error message about CMOS checksum being bad. This error is usually caused by a dead (empty) CMOS battery. This battery lasts for 3 to 5 years. Some says that it even lasts for 10 years. Whatever the case, you will need to replace the CMOS battery (also known as BIOS battery). The CMOS battery is usually located at the motherboard. Some under the laptop compartment while in other models it's located right underneath the keyboard. In the case of IBM thinkpad R31 laptop, it is located under the keyboard. So, you will only need to disassemble the laptop keyboard to have access to the CMOS battery. Here is the exact error message that show up once you open up an IBM Thinkpad R31 laptop that has a CMOS battery problem:
Error Message: 0251 System CMOS checksum bad - Default Configuration usedScreenshot:
Change the CMOS battery
How to access the CMOS battery of IBM Thinkpad R31:
1. It is advisable to remove the laptop battery first:
2. Unscrew the keyboard. There are two screws underneath the laptop that are holding the keyboard. See picture above. I encircle the two screws that you need to remove.
3. You can now remove the keyboard but be careful because there is a flex cable attached from the keyboard to the motherboard.
3. You can now remove the CMOS battery. It is the one wrapped in a yellow plastic. It is glued to the casing underneath so you will need extra force to remove it. You will also need to remove the wire connection.
4. Cut the yellow plastic to reveal the battery. Change it with the same model (CR2032). It is the same battery used in desktop motherboards. If you have spare motherboard lying around, you can safely use the battery from it provided that it is still holding charge. I use electrical tape to replace the yellow plastic thing.
I hope this article helps you. If you need to access other parts of the IBM Thinkpad R31 laptop or you need the complete disassembly guide or service manual you can download it below:
Download Disassembly Guide | Service Manual | IBM Thinkpad R31: