How to Check for Faulty Components

Hi,

I recently dropped my iphone 6 plus in the ocean when I fell off a dock. Since it's salt water, I took it home and cleaned the logic board. I can't see any corrosion except for one of the antenna wire ends.

So I put a new battery in it and plugged it in after a few days of drying and it "kinda" worked. The screen wouldn't work at all but at least iTunes was now recognizing it as an iphone in recovery mode. I tried to restore it but it would error our and never even start.

After a few days it wasn't even being recognized so I changed the charging port/headphone piece. It still doesn't work and it's still not getting recognized by itunes.

I guess my main question is this.... Where do I even begin troubleshooting for the components that are faulty? All I know is that it's not the battery or the charging port.

I already got a new phone so I'm not in a rush and wouldn't mind learning something but I just don't know where to start. Any help would be greatly appreciated, thanks!