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

T420 / T520 - External screen blank during boot up. (Nvidia Optimus & Laptop Docked)

Question

When using the T420 / T520 on the docking station with external monitors connected via DP and VGA ports. The boot up screen is not showing even with the laptop lid close. Boot up screen would only show on laptop screen.

Answer

This is a limitation of Optimus capable systems.

The reason is that the integrated graphics processing unit (iGPU) is providing the signal to internal LCD.
The discrete GPU is linked to the DVI, DP ports (attached screenshot), so that is why the only setting available for Optimus is the "ThinkPad LCD". We have tested all possible settings and we can confirm, that the "Boot Display Device" is always offering the correct available options. Integrated and Optimus settings allows the integrated chipset to drive the internal LCD. Discrete offers the whole variety like analog VGA, digital on dock etc.

If it is important to have the ThinkPad logo displayed at boot in your particular configuration, the BIOS will need to be set to discrete video. 

 

Optimus_calpella.png

 

 

BIOS Setting;  Config -> Display; set Boot Display Device to Analog (VGA),  Graphics Device to Discrete Graphics.

 

Capture.JPG

 

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Comments

PD66 On 2016-11-22, 4:06 AM

hello :) I am having all kinds of problems with my T420 right now my screen is showing : An operating system wasn't found. Try disconnecting any drives that don't contain an operating system. Press Ctrl+Alt+Del to restart. I do and it returns back to this screen. Then I get to startup interrupt menu. Help??? Thank you Paula DeBrackeleire

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