How To Check CMOS Checksum Error and How To Fix | With Video on POST


A CMOS checksum error is an error of computer motherboard (MOBO) that will cause to halt during power on once the Power On Seft Test (POST) will display. This will cause your computer not to preserve the time and date module using the BIOS and other important settings of your computer. Like the shared memory of the display or the VGA. And this will probably cause to hang up your computer and expelled in the browser because of invalid time and date. Learn here what is the cause, how to check, and how to fix.

In this post you will learn how to check and fix this problem of computer. Just follow the procedures below:


After you press the power button the computer will conduct Power On Self Test. When there are error found during the process the computer will halt and it will display CMOS CHECKSUM ERROR. So to test it and what is the problem. See it below or use the video post above here.
  1. As a safety procedure, turn off PC and unplug the power cord.
  2. Then, if you can remove the motherboard from the system case, remove it. Or you can remove directly the 3 volt lithium dry cell CR2032. This battery is used to power the CMOS/BIOS IC. So that the computer will preserve the default settings like the time and date modules. See the video above here.
  3. Then check whether the 3 volts is exist using the multitester or volt meter. Then calibrate your tester to the DC volts. And test the battery, remember being sure the correct orientation of the probe tester. The battery has a positive and negative part. So the black probe of the tester puts it at the back or rear part and the red probe puts at the top that there is a plus (+) symbolic.
  4. Check the 3 volts using the multitester meter scale if pointed to the 3 volt scale. 
  5. If the meter scale pointed below the 3 volts, you need to replace the battery with the same part number I stated above. 


  1. After you replace the battery, you need to setup the BIOS settings using the BIOS interface. Power on your computer, after the POST will display, press the "DEL" or the "F1" key. Check also the setup key of your computer BIOS. Because every motherboard has a different setup key. Check the video above here.
  2. Then go to main menu or find the menu where the date and time you can setup into the current date and time. You can disable also the drive that doesn't use, like the micro floppy diskette. Check also the detection of all drives you connected to your motherboard, including the detection of main memory (RAM) and the processor information.
  3. Setup and change also the shared memory capacity of your video display or the Video Graphic Adapter (VGA).
  4. Then setup also the boot sequence of the drive. If you're using multiple drive, probably you will encounter a "boot up" error. Because the POST can't find the startup files during the bootstrap of the operating system. 
  5. Then don't forget to save the BIOS settings you made. You can press the "F10" or the exit menu to save.
  6. Now the computer will restart, then check whether the POST will not display the "CMOS Checksum error". You can also turn off the PC, then power on again and check if the error will not exist. If there are no errors, the computer will boot immediately to the Windows as your operating system. Note: If the error still exist even the CMOS battery is new, there is still a problem with the motherboard, probably on the circuit connection of the CMOS or the CMOS socket alone. To fix this check the below procedure or see the post video above here.

  1. Power off and unplug PC, then remove the motherboard. You need this because you need to find what is the cause of the error.
  2. Then when the MOBO is pullout now in the system case, remove the CMOS battery. Check any dislocation or cut of the CMOS socket IC.
  3. You can also check the connection of the CMOS circuit using the multitester resistance check. Check the deplection of positive (+) and negative (-) pin of the CMOS socket that soldered at the top and the bottom part of the board. Check the post video.
  4. If this is connected, probably the battery is loosen to the positive pin. You can tighten it by pushing it to the battery. Be sure whether it is tighten now.
  5. You can clean also the CMOS IC by removing it, if it is socketted, you can clean all pins. Note: be carefull in removing this IC and be sure to remove the CMOS battery before doing this procedure.
  6. Then discharge the CMOS/BIOS to back the settings to the factory default. Follow the procedure on this link: Check on the CMOS/BIOS Jumper procedure part 11 of Parts and Functions of the motherboard.
  7. Then connect again the PSU, don't connect the HDD. You can power on without the system case by grounding the 2 pins of power_on of FRONT Panel connectors. Check on the Post Video.
  8. If the problem still exist, repeat the procedure here.

This problem will exist in most cases of the old motherboard. The main cause is overheating the CMOS/BIOS parts, dust buildup and corrosions of the CMOS IC pins. Some motherboard also needs to update the BIOS system. If you want to use again your old motherboard, you can fix this problem by doing the procedure above until it will fix.

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How To Check CMOS Checksum Error and How To Fix | With Video on POST combinebasic 5 of 5
CHECK CMOS CHECKSUM ERROR A CMOS checksum error is an error of computer motherboard (MOBO) that will cause to halt during power o...
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I'm a husband, a blogger and Biomedical Machines Specialist, also a computer instructor and technician and a crazy writer, I like to write and build blogs and avid fan of social media. I have built this blog just to help others through information. Follow us on Facebook and Twitter.

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