In A1707 the location of the mosfets is right under the keyboard connector (oposite side of PCB). In my case the components were still there, but the left fan was running at full speed all the time. Did a reflow (apply solder paste and then hot air with SMD solder station) but it did not work. So, I bridged the Drain pins of both mosfets and now both fans are controlled by the right side driver. There are test pads for the Drain pins, so solder is easy by bridging those pads. The laptop seems to be working fine with both fans controlled together, but you can install Mac Fan Control or similar app to assign more sensors to drive the good mosfet.