I had the same problem and was just able to fix it.
By pushing the charger-jack to the direction of the display or pushing on the phone close to the same jack sometimes the GPS still got some fix. So it seemed that my GPS antenna was somehow disconnected.
The antenna seems to be a plate which is located in the inner frame of the phone (see here https://www.youtube.com/watch?v=zeBC3pcs434 on1:24). I cleaned the contacts located in the frame as well as on the side of the maonboard and bent them a little bit towards the frame. I guess the most important one is the golden one right under the charger-jack (see 1:41 on the very right side).
Since then its working again ;)