Not the first time
I had a similar fault on my 4S, changed the wifi/bluetooth chip and it seemed to work but obviously the wifi didn't because the chip was made by Chin G Knockoff (tm) not Apple.
Did a firmware update hoping to fix it and the phone then went dead, black screen and everything.
I could still see it on Itunes but it was basically unusable.
Previously to this everything else worked so pretty sure my soldering-fu was adequate.
The only interesting problem was two very small missing smd resistors which were just too small to solder back on, apparently they have to do with chip enable.
There are rumors that aftermarket batteries will do this as well, one of the reasons Apple shops destroy their old ones is that the chips can and do get reused so the "knockoff" battery will work correctly despite having a potentially unsafe cell.
Biting the hand that feeds IT
