Check resistor damage in line home button to ram u0201, this line connect 1,8v sdram. This line problem iphone not power on "dead". If there is a short-circuit capacitor, then the home button is automatically always in a closed state (keep pressing). This results in GPIO failing in reading input data in other words error. For lcd replacement, the socket to the connector should be precise, because for the lcd line the voltage used is quite large, even without the battery the capacitor still supplies the residual charge when loaded. Keep the spirit and always be careful. Learn about ic that is sensitive to '''esd''', maybe this one cause. Tq