Chosen Solution
i always repair u2, but this first time i get this mysterious case,, the problem before iphone 7 not charging pp5v0_usb only 4.5 volt removed tristar but not fixed remove the mosfet Q4001 i get 5 volt direct jumper pp5v0_usb to pp5v0_usb_rvp the problem back again and i get only 4.5 volt and 100 percent u2 problem,, change u2 problem fixed but i get no imei in *#06# and no modem firmware,, this baseband issue this board “never” repaired before and im first hand repair this board i use 350 temp for take off this ic and 280 temp for installing new ic u2,, i always do that and never get problem for baseband what next step for repair this?
From the information you have provided it is highly unlikely you have damaged the baseband CPU. There is a pad under Tristar that sends some kind of data to the baseband CPU. I would start diagnostics by checking the power rails on the baseband PMU than reflow Tristar and give it a slight nudge.
this happens when you cold joint the tranciever. The tranciever for the intel modem sets the rffe clocks. If the clocks are distorted the frequency changes hense no service or functioning modem. Reball the tranciever and you will be back up and running.
