When doing these repairs, sometimes small things can happen to impact the functionality of the device. If you have performed a repair and are getting a black screen yet the phone itself is still making sounds and functioning, the screen itself may have been damaged when doing the repair. The first step in these situations is to identify exactly what has happened. Please clean off the connections both attached to the screen through the flex cables, and the connectors that those flex cables snap onto on the logic board. You can do this using a little alcohol and a q-tip but BE CAREFUL! These connections need to be cleaned delicately as to not damage the brass connection pins. If these pins get broken, bent or damaged in any way, it will not allow the screen to work.
After you have cleaned these connections, please try to re-connect the flex cables stemming off of the screen assembly back onto the logic board. Once connected, move through the steps until you are able to test the phone and do so.
If you are still experiencing problems, please reach out to firstname.lastname@example.org so our representatives may help you diagnose this problem further.