LCD working only when battery is fully discharged

Hello everyone,

I have an iPhone 7 and it had some problems with LCD before - there was some stripes and noise on the screen sometimes. But now after changing back cover it looks like screen is not working when phone is booting nor when phone is fully booted. I have some positive feedback like phone vibrating when home button is pressed or recognition by PC, sound is working but screen is just black without backlight.

Only time when screen works is when battery is drained and phone is showing charging icon. When battery gets to current where iPhone turns on then screen is dead.

I tried different screen but same result. Problem has to be on MB. Have anyone ever seen something like this before?

Thank you for any ideas.