You've already gotten far more "intimate" with your radio than most people. Changing batteries is about as sophisticated as we usually get.

Unfortunately without schematics there's not much you can do to troubleshoot the transmitter at a component level even if you knew what you were doing. Of course since it's proprietary you can't get the schematics.

If you had a DX6i or a DX7 you could simply bind the Vapor to the better transmitter. Of course you're still saving for one, so that's out.

I would recommend you contact Horizon Hobby support. They should be able to take your transmitter and fix or replace it under warranty. In the meantime you can use the MCX transmitter to fly the vapor.