In this video we are showing how to fix doesn't power on iPhone 6s plus by re soldering HDD IC.
Once agin the question rises how does i diagnosed this phone?
The user informed me that the phone was bricked by dropping it.so first i Connect it to iTunes and it connected automatically in DFU mode with no serial number.so restored and it ends with the error 4005. Indeed the serial number is programmed in HDD(flash chip).so it indicates that the issue was with HDD(flash chip) because the phone was dropped by user. It means the HDD(flash chip) might be disconnected with PCB so I removed the HDD(flash chip) and resoled (reball flash chip) it.
The whole process of resoled you can see in this video. After this process the phone turned in RECOVERY mode so it need to restore once agin now it completed without any errors and phone turned on .In this process you are going lose all data of your phone.
NOTE :- This work should be done by only professional technicians other wise you gonna brick your phone