Anthony Zara, You say the whole assembly was replaced, was the flex also replaced? It’s a pain, yes, but you’ll have to open it up again.
When problems like this arise, I start by opening it back up and do a close inspection of all connections. Even the tiniest of dust particle in the wrong place, can prevent a connection from being made.
Use some >99% isopropyl alcohol to really clean the connections. Rubbing alcohol and such aren’t good enough, as they contain many additives. When it’s dried off (only takes a minute, as IPA of that concentration evaporates quickly) reseat the connections (making sure to get a good connection) and test the iPad again. Test it before closing it back up.
If it still doesn’t work, take some good quality and up close pictures, then update your question. [guide|21499|Adding images to existing questions].