for example my GN:
1) tempreture too hot (will feel uncomfortable hot when u calling or surfing more then 10 minutes)
2) Camera having a red Spot when taking photo
3) LCD changing color (especialy white)
4) S PEN!! (no need to touch screen but already written)

IF u having this 4 problem, u have to send in the phone.

For my case (solutions):
1)  tempreture too hot due to the PCB board (replace the PCB)

2) it should not appear red spot (replace the camera)

3) LCD changing color would be special case, in my case my LCD color totally changed, for example white is not white, it appear to be some green, a very light green. (replace the LCD)

2nd case : when u look at the white color, it appear to be flashing, white contain some green and white and green keep flashing (this 1 totally cant be fix by samsung, as what i know so far)

4) S-pen (replace the S - pen)

This is from my experience. MY GN changed this 4 parts.

PCB, camera, LCD (twice to fix the flashing issue, but failed) and S-pen

Note: IF anything wrong please forgive and remind me to correct my wrong.

Thanks