Hi.
I have a One S with no power issue.
I checked the mosfet, they all read 0.554
I found there was a blown diode near the nand.
Replaced it.
But found out the new one is still heating too much I had to cool it with alcohol.
I also found that there is no 3.3v.
You can see the new blown fuse.
I replaced the u4d4 and all the components around to no avail.