How to Fix CMOS Checksum Error | Invalid 502

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How to Fix CMOS Checksum Error | Invalid 502

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How to Fix CMOS Checksum Error | Invalid 502

How to Fix CMOS Checksum Error | Invalid 502


On the motherboard of the computer is a semiconductor chip called a complementary metal oxide semiconductor (CMOS). The primary purpose of this chip is to store BIOS-related settings and data. Additionally, it keeps the BIOS powered on even while the machine is off.

As a result, any changes you make to the BIOS are noted in the CMOS. Usually, the CMOS records a series of numbers when a computer is shut off. The CMOS will compare this set of numbers with the numbers that the BIOS created the next time a computer is turned on. Should the figures not line up, an error message will appear on a black screen.

'' CMOS checksum error - Defaults loaded ''
'' CMOS checksum is bad ''
'' CMOS checksum is invalid ''
'' CMOS Reset ( 502 ) ''

You will always receive the same problem message when you restart the machine. This could be caused by a malfunctioning or dead CMOS chip, or by corrupted CMOS values. Owing to any of above causes, the computer will not only refuse to start up but will also display incorrect times because the CMOS battery powers the computer's internal clock.

I'll be teaching you How to Fix CMOS Checksum Error | Invalid 502 in this article. By the time you finish reading this article, you will understand how to fix the 502 problems in the CMOS checksum that prevent booting.

Now let's discuss the subject,

1. Replace CMOS battery

The tiny button-type battery, or CMOS battery, is often located on the motherboard. It often comes with the CR2032 3V model number. 


The typical lifespan of a CMOS battery is more than five years. After this time, the battery might not perform properly and won't be able to provide the necessary power for the computer to turn on. 


To fix this, just buy a new CMOS battery from a computer retailer and replace the old one. It is simple to locate a replacement CMOS battery for a desktop computer. yet not when it comes to a laptop. 


Certain laptops require expert assistance in order to replace the CMOS battery. However, ensure sure the CMOS battery is fully dead before replacing. 


In order to inspect the CMOS battery,

1. Turn on the computer
2. To access the BIOS Setup Utility, press and hold the F2 or Del key
3. Find the System date and System time on the menu

It is obvious that the CMOS battery has failed if the system time and date are off. 

2. Reset BIOS

Resetting the BIOS is the second method you can try to fix this problem. The BIOS's values aid with the system's bootup. Numerous factors might lead to the corruption of the boot values. 


Among these include malware assaults, incorrect BIOS updates, and unexpected power outages during BIOS updates. For any of those causes, the BIOS values will get distorted and the boot process will stop working. 

Therefore, you can simply resolve this by returning the BIOS to its original settings. There may be a switch on some motherboards that can be pressed to reset the BIOS. 


The BIOS will also reset if the CMOS battery is removed if the switch is not detected. Aside from that, using the BIOS Setup Utility is the simplest approach to reset the BIOS.

To reset your computer's BIOS, 

  1. Turn on the PC
  2. To access setup, press F2 / F8 / F10 / Del (the key varies depending on your computer type)
  3. Press F9 to access Setup defaults and reset the BIOS when the BIOS loads
  4. To save and exit, press F10

You have now successfully reset the BIOS to its original configuration.



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