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The Lenovo ThinkPad T490 was released in October 2019, and has 2 different versions. The T490 has an Intel CPU, while there is a T490s with an AMD CPU.

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Screen does not display but display on tv HDMI

Laptop in on but does not display on screen but display when connected to tv with HDMI

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When did this start? Has the laptop sustained any damage, either physical or liquid? Did anything happen around the time the screen quit displaying a picture?

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Hi @kahisomotake

With the laptop turned on and the display switched back to the laptop screen i.e. black screen, try using a flashlight at an angle close to the screen to check if you can see any images on the screen at all.

They will be very faint if they are there to be seen, so trying this in a darkened room may help to see them.

If you can't see any images then there's a problem, either with the LCD cable, e.g. loose connection either end LCD panel or motherboard, damaged where it passes through the hinge to get from the board to the LCD panel or with the LCD panel itself.

Here's the hardware maintenance manual for the laptop.

Go to p.90 (96 of 117 pdf) onwards to view the procedure to remove the LCD panel etc. This will allow you to inspect the LCD cable and the connections.

If you can see images then there's a backlight problem, with the screen. Either a faulty backlight power supply on the motherboard (blown fuse perhaps?, a faulty LCD cable/cable connection (cable connection, one end of plug not fully inserted into socket, either end motherboard or panel) or a faulty LCD panel.

Here's an image from the schematic showing the motherboard's LCD panel backlight power supply circuit.

As can be seen fuse FS102 supplies power to pins 36-39 of the LCD connector. Check if there's voltage seen when measuring on those pins. Be careful not to short them out with the test probes.

Block Image

(click on image)

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