Try to find diode readings for the fpc connector the lcd is connecting too.
Meter in diode mode and put red on ground and black on fpc connector. Careful not to damage pins. Sometimes their is OL on the diode readings and you can have a missing filter on one of those lines and not know it. If you don't find anything wrong in the diode reading. Inspect and trace back any OL pins and look for missing components
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If that is all ok, you might want another testing working lcd to test with. I believe completely dead battery can cause no display as well.
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If that is all ok, you might want another testing working lcd to test with. A completely dead battery can cause no display as well, putting device into dfu mode and leaving plugged in to a computer overnight can help charge battery
Try to find diode readings for the fpc connector the lcd is connecting too.
Meter in diode mode and put red on ground and black on fpc connector. Careful not to damage pins. Sometimes their is OL on the diode readings and you can have a missing filter on one of those lines and not know it. If you don't find anything wrong in the diode reading. Inspect and trace back any OL pins and look for missing components
If that is all ok, you might want another testing working lcd to test with. I believe completely dead battery can cause no display as well.