So I have an iPhone 6S 64gb bought from eBay. The problems are:
* it would reboot or turn off after lock screen
* can’t update via iTunes(error 9), 3uTools(error -1) or even on iPhone but I can restore it.
* phone heats up quite fast
* battery and LCD have been replace but still the same symptoms
So I suspect is a hardware issue related to the motherboard but where and how much will it cost me to fix this.