Hi, right i have this issue many times and only recently managed to repair it. I've been fixing iphones for several years but I cannot solder for the life of me.
I found the various pictures around showing you where to make a jumper on the logic board (just above the digitizer connection on the logic board. It's a tiny little metal pin that sticks up slightly from the board (sorry dont know the techincal term for it)
Anyway all the guides and posts just kept saying 'make a jumper here' which to me didnt make sense and as I cant solder i was really stuck.
So my solution : which has worked on 11 devices now with same issue. I bought a Nickel Conductive Pen from ****. I dropped a very small amount of the fluid from the pen on top of the tinny pin above the digi connection and allowed it to dry.
Hey presto it works. The pin is obviously very close to the connector and is very easily damaged when removing the connectors the LCD and digi. Its so small you wouldnt even know you had damaged it. But I can confirm 100% that a Nickel conductive pen with a small blob on the pin makes the cameras work