Poor wifi signal - not "greyed out"
I looked everywhere for any answer, but didn't find any solution. My iPhone 4S gets very poor wifi reception. I'm able to connect to my router only when I'm literally next to it.
I changed the wifi flex (top right corner), tried cleaning EM shield with alcohol and tightening it's screws.
The phone is not new, and the screen was most probably changed - some screws were missing.
Anyway, which parts (even tiny) and screws are anyhow related to to wifi signal strength? Which part/s of the phone work as a wifi antenna? What else can I try to do to fix it?
Thanks for any advice.