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ThinkPad NotebooksThinkPad T400 / T500 and newer T series Laptops Knowledge Base

T420s - Screen refresh rate drop to 50Hz when on Battery


The T420s screen refresh rate is dropping to 50Hz when on battery despite setting "Never" change Refresh rate when on AC on Lenovo Power Manager.


This symptom  has been resolved through the latest version of video drivers and power manager on the support site.  Download and install the latest version for your specifc OS. Here is the link to the drivers for T420s


After installing, reboot system and test functionality - you should now be able to change refresh rate settings.


Intel GPU.png


The following steps should now no longer be required and are included for historic reference:


A previous work around solution was to change some values in the inf files by follow steps provided below:


  1. Download latest display driver on the support site.
  2. When the "exe" file is downloaded, double click the file, Accept the agreement and extract it to path (C:\DRIVERS\WIN\VIDEO\INTEL\Graphics)
  3. Once the extract is complete, untick the "Install ThinkPad Video Features now"
  4. Click Finish
  5. Click Windows Button, type "run" on the search bar
  6. Paste the following "C:\DRIVERS\WIN\VIDEO\INTEL\Graphics\kit32889"
  7. Open file named "kit32889.inf" - The file size is 87kb
    Capture 10.JPG
  8. In notepad, press Ctrl + F and search for 0xF900 and press enter
    Capture 11.JPG
  9. Change 0xF900 to 0xF940
    Capture 12.JPG
  10. Press Ctrl + s to save the changes and close the notepad.
  11. Once the file "Kit32889" has been changed. Go to Programs and features and uninstall the previous version of the graphic card driver before you install this modded version.
  12. Once the previous version has been uninstalled and the laptop has been rebooted. Follow the steps provided below.
  13. Click Windows Button, type "run" on the search bar
  14. Paste the following "C:\DRIVERS\WIN\VIDEO"
  15. Double click on the "Setup.bat"
  16. Press Yes to install the driver, select the language you want Catalyst to display then click Next.
  17. Click Install
  18. Tick Express and click Next.
  19. You will receive a prompt that Windows can't verify the publish of this driver.
  20. Click "Install this driver software anyway"
    Capture 5.JPG
  21. After clicking install this driver software anyway, the installer will continue to install the drivers and you will receive a prompt to reboot the laptop once it is done. Click Reboot.
  22. The Intel GPU's refresh rate would not change to 50Hz when running on battery.


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