Thanks for all the help. I tried all the above advice but no luck. I decided to bring the phone to the shop (not authorized apple repair center). They tried software updates but the phone is not responding to Itunes. Failed hard reset, failed DFU mode. So he took off the back cover, remove more screws and off the logic board circuit. Probe a few points with the multimeter and there he said something about energy/power chips. He then asked me whether I charged the phone with any 3rd party chargers? Car charger? Quite impressive...
He is going to replace a chip and the damage is about USD120 (after conversion). He assured me the information in the phone will not be removed. Holly cow, what else can I asked for. Using tweezer and hot air gun, he then removed a BGA chip near the "A4 apple logo chip". I have the photograph.
He then clean the BGA pad, clean the BGA chip (i suspect it is used chip), used a metal stencil to arrange the flux and BGA onto the cleaned chip, cool off and remove the stencil. Looks neat though. Finally install the chip with the hot air gun. True enough the phone reboot with apple logo, battery remain at about 60%, all information remained as it is.
The whole process took about 30 ~ 40min. Anyway, hope this help. Thanks...
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