Hi, this is a common issue with the baseband or baseband power management. Ways to diagnose this issue 1) go to settings, general then about and see if you have modem firmware listed 2) type *#06# to see if your IMEI is displayed both of these issues require good board level repair skills.
Hi, when you replaced the screen did you desolder the sleep magnetic induction flex and transfer to your new display, if not this will be the main cause for your problems. A image of the flex is attached. It’s located at the bottom of the lcd
Hi, Are you using the original charging port? A lot of times the replacement chassis come with charging port connection issues, this will cause no service issues and also cause the boot loop your describing. If you transferred over the old port you need to go back and check it for any tears.