Wii u gamepad blue light fades out after power button is pressed

I bought a Wii u gamepad to try and fix it. The blue light fades away after the power button is pressed. I tried a different working motherboard and got the same issue. Tried a new lcd and digitizer, same issue. Tried a new battery, same issue. I read on here that it's a bad lcd that causes it but not sure if that's true. What could be the problem with it?

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