Original post by: Minho ,
The iPhone has the GSM antenna embedded within the housing. Depending on where you got the housing, it is always possible that the housing is of low quality. The other possibility is that you missed a step when you re-assembled everything back together. All of those tiny screws are critically important when it comes to the antennas because they are what allows the antenna path to connect properly. I would recommend you go back through the various [[Topic:iPhone 7 Plus|guides]] to insure you didn't miss anything. Worse case, you could put things back in the original housing to see if everything works properly. If it does, then the replacement housing may be the issue.