CMOS (502) Error Message

[Hornet1027]

Desktop boots up twice; one to a black screen (with a CMOS 502 error), and once I am prompted to press "Enter", it boots up again normally to Windows and then functions normally.

Opened the desktop and there is no CMOS battery to replace.  I have updated the BIOS to the latest version using the HP Diagnostics Tool.  The CMOS (502) error persists.  How can I fix this issue.

[Jerry_57 · Accepted solution]

Hi @Hornet1027,

Welcome to the HP Support Community.

Thank you for posting your query. I will be glad to help you.

The HP CMOS (502) error indicates that your BIOS settings were lost due to a power failure on the Real-Time Clock (RTC). Because your desktop lacks a physical coin-cell battery, it relies on either a specialised RTC capacitor, a dedicated RTC battery chip, or the main power supply trickle.
 

Follow these steps to resolve the issue:

1. Hard Reset the System Board:

A hard reset drains residual power from the motherboard capacitors and forces the BIOS to reload safely.
 

• Shut down your desktop completely and unplug the power cord from the wall.
   
• Press and hold the Power Button for 30 to 45 seconds.
   
• Plug the power cord back in and turn the PC on.

2. Enter BIOS and Reset Defaults:

If a CMOS error occurs, the BIOS settings must be reset and saved.
 

• When the computer boots and prompts you to press Enter, do so to enter the BIOS menu.
   
• Look for an option that says Load Setup Defaults or Reset to Default (usually triggered by pressing F9).
   
• Press the appropriate key to save and exit (usually F10).

3. Check Date and Time:

Incorrect time and date settings are a primary indicator of corrupted CMOS data.
 

• Once booted into Windows, check the bottom-right corner of your taskbar.
   
• If the date and time are wrong, click on them, go to Adjust date/time, and ensure "Set time automatically" is toggled on. 

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