1.CS
2. CPU
3. COMBO FLASH
-1. It may be in "contact service" so, it's on good place i hope
You should check it on Wintesla, or eeprom tools, sou you get reason for CS if any.
-2. Badly soldered CPU/or bad CPU by it self.
-3. Same for combo flash.
Try writing good full backup fron working phone first.