Recently acquired an iPhone 6 with weak 2.4 and 5GHz wifi, Bt, GPS, and cellular signal. After studying the design, there are few ground and antenna contact points that needs attention after drops or just age. Generally, no new parts are necessary (likely just remaking better connection while replacing parts) In my case, just fluffing up a couple of ground contact patch area fixed it. Here is a pic and link to the summary
https://drive.google.com/file/d/1lLlRpKdSlORiMFwZLOj1fFIYmIqWF6xv/view?usp=sharing
[image|2301858]