CPU Clock slows down to 400MHz when the Laptop plugged in. It works normal while using battery.

[emirhan1]

Hello everyone,

My HP Pavilion Gaming laptop suddenly started slowing down about a week ago. I have been trying to fix the issue since then, but I am still not completely sure what the problem is. Below is the troubleshooting process I have followed so far:

• I installed HWMonitor and observed that the CPU clock speed drastically drops when the laptop is plugged into the charger. When running on battery, the CPU works normally.

• I checked the BIOS settings and version, but there are no advanced BIOS options related to power management. HP seems very strict about hiding BIOS settings from users.

• I ran the HP PC Hardware Diagnostics UEFI tool to test the power system, and it reported an error: "This is not an HP AC Adapter."

• I also tested the battery, which returned an error stating something like "This adapter is in bad condition or it is not original."

• Before these steps, I already had set the Windows power plan to Ultimate Performance using PowerShell, and manually set all power settings to "Maximum Performance."

I would greatly appreciate any help or advice to identify and fix the problem.

[Max3Aj]

@emirhan1, Welcome to HP Support Community. 

Thank you for posting your query, I will be glad to help you. 
Based on your detailed description and the diagnostics you've already run, the issue you're facing, CPU throttling to 400MHz when plugged in, is most likely due to the AC adapter not being recognized as genuine or functioning properly. Here's how you can resolve it:

Root Cause

Your laptop is detecting the AC adapter as non-HP or faulty, which triggers a power protection mechanism that severely limits CPU performance to prevent hardware damage.

Recommended Steps to Fix

Replace the AC Adapter

• The error message from HP UEFI Diagnostics (“This is not an HP AC Adapter”) strongly suggests the adapter is either:
  • Not original HP hardware, or
  • Damaged and not delivering the correct wattage.
• Solution: Purchase a genuine HP 150W Smart AC Adapter which is compatible with your model. 
  Check here

Update BIOS and Chipset Drivers

• Even if BIOS settings are limited, updating the BIOS and chipset drivers can help resolve power management bugs.

Official HP® Support

• Download and install:
  • Latest BIOS
  • AMD Chipset Drivers
  • HP System Event Utility

Reset BIOS Defaults

Sometimes, BIOS settings may get corrupted:

• Restart your laptop and press F10 to enter BIOS.
• Choose "Restore Defaults" or "Reset to Default Settings".
• Save and exit.

Check Windows Power Settings Again

Even though you've set it to "Ultimate Performance", double-check:

• Go to Control Panel > Power Options.
• Click Change plan settings > Change advanced power settings.
• Under Processor power management, ensure:
  • Minimum processor state = 100%
  • Maximum processor state = 100%
  • Do this for both Plugged in and On battery.

Inspect for Overheating or Dust

• Clean the vents and fans using compressed air.
• Overheating can also cause CPU throttling, though in your case, the issue seems tied to power input.

Optional: Test with Another Genuine HP Adapter

If you can borrow a compatible HP adapter from a friend or service center, test it before purchasing a new one.

I hope this helps. 

Take care and have a good day. 

Please click “Accepted Solution” if you feel my post solved your issue, it will help others find the solution. Select "Yes" on the bottom left to say “Thanks” for helping! 

Max3Aj

HP Support