Hello, This google Pixel 3XL I have had a damaged lcd but the screen was still visible it was just cracked. I went to do...

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It appears that the display would not come on completely until the back cover of the phone was put into place and the capacitive pins on the touch ID sensor were making contact, very strange issue, but once all together the problem was resolved, and the display came back on phone appears to be working fine.

With Face ID on the iPhone you will have to have the original Face ID components from your original display. It is not uncommon for some repair shops to damage these components when they are transferring them to the new display as they are fairly easy to damage if you are not being careful. So if they didn’t transfer the original Face ID components from your display, or if they were damaged when it was replaced then it won’t be possible to get Face ID back on your phone to my knowledge. This is because those parts are paired to your logic board on the phone, the only way to get it back would be potentially repairing the original Face ID components and there are not many places that would be able to do this.

There could be a few causes, the most obvious being the OLED screen could have damage underneath the glass that is keeping the screen from powering on and in this case you would need a display replacement. Another possibility is it could be software related have you tried to do the soft reset of the phone by tapping volume up then volume down and holding the power button until the phone power cycles? I have seen a few instances where this happens and does fix the problem. The only next step that you could take would be opening up the phone and reconnecting the display connections to make sure nothing came loose if that doesn’t work then you definitely need a display replacement.

It seems to be that the issue was motherboard related, something appears to have just failed, I didn’t have the time to trace every power rail and distinguish exactly which part failed on the motherboard itself, but after talking with a few other people and more research it appears to have happened to multiple of these laptops usually after some sort of update. Still not exactly sure what the problem was but replacing the motherboard solved the issue, so the battery was good but somewhere power must have not been going properly.

It appears that during the process of completing the repair for some reason the OS for the phone was wiped. I was able to put the phone into recovery mode, and then applied and update using adb. I downloaded the latest Oxygen OS for the phone and used ADB Sideload to be able to update the phone and now it works like a charm.