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CMOS Checksum Bad
Description
The CMOS memory checksum is bad, typically indicating the CMOS memory data is corrupted or lost. You may also see the secondary message that the Date/Time is not set.
The BIOS will automatically use a set of defaults that normally work fine, but you will often be forced to go into the BIOS setup to make sure the settings are what you want and set the date/time.
Sample Screen
CMOS Checksum Bad CMOS Date/Time Not Set
Key Facts
Full Title
CMOS Checksum Bad CMOS Date/Time Not Set
Type
Fatal BIOS
Windows
All
Vendor
Unknown
Solutions and Fixes
Solution 1 of 2 - Save and Exit BIOS Setup
On some systems, if you press reset or disconnect the power during the early startup or power down process, the CMOS memory is corrupted. Proceed into the BIOS setup (BIOS Access). Check that the date and time is correct and update it if not. Make any other changes you wish or just use the defaults, and select the Save and Exit option. If the problem does not reoccur, consider it solved.
Solution 2 of 2 - Replace the CMOS battery
If you performed solution 1 and the error occurs again after a complete power down (i..e. removing the power cord), the CMOS battery is likely bad. Most systems use a small coin style lithium battery. These often last 3-6 years, but at some point run out of juice and need to be replaced.
For desktops, your system manual or motherboard manual should specify the type of battery and location on the motherboard. For laptops, it is often very difficult to access and may require a professional to replace it.
To replace the battery on a desktop system:
Turn off the system and remove the power plug.
Remove the case or side panel to access the motherboard.
Look for a round silver coin cell, typically in a black holder.
Remove the battery while noting which way the battery is located. You may need a small flat screwdriver to release the side clip.
Install the replacement battery with the same battery type, being careful to insert it in the same direction as the removed battery (or using the polarity marked on the holder or manual).
Reassemble the case and power.
Turn on the power. You will get the CMOS Checksum Bad error once more, but it should be the last time. Go into the BIOS setup and set the date and time, and any other options you prefer.
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