As such, I guess the WiFi device (the chip on the CPU board) is not broken! But what most probably happened is the small antenna located in the top of the screen is not anymore making a proper connection with the CPU board. Hence the weak WiFi symptom...
Originally Posted by lu
The WiFi (and Bluetooth) antenna is a small metal foil stuck to the touchscreen body. As can be seen on the first 2 pictures, one end is curved so it will make a spring loaded-like contact with the CPU board.
However, the one end of the CPU board making contact with the antenna is not fixed and is subject to vibrations. I guess too many / too big vibrations (a shock) are likely to damage and even break the spring-like end of the antenna (3rd picture), leaving a poor contact between the antenna and the WiFi chip...
Manual fix is still possible, though, if you are "brave enough"... ;-) (I did it, more pictures available if you ask)