Display problems after screen replacement ZTE ZMax Pro

My nephew replaced the broken screen in my ZTE ZMax Pro. He has done this in phones for me in the past. This is the problem that has us stumped. (I say we, he knows a lot more than I do, but we are both learning) Display is clear and touch works fine, until the screen times out or the devices is restarted or powered back on. The screen is black and white with vertical lines. When I see him, he takes the back off and disconnects and reconnects something on the battery. On restart the screen and display work fine until it times out or is powered off. Any idea what is causing this, or where I might find an answer?