Component A is a 1uH inductor in early versions of the Duet WiFi. In later versions of the Duet we use a ferrite bead instead, part number MFB-201209-0011PW . Component B is a Schottky diode, part number DB2W40300L.
I suggest you measure the voltage at the junction of the 10uH inductor (the grey square marked 100) and the 1uH inductor. If there is 5V at that point, then you should only need to replace component A. Otherwise you will also need to replace the diode and the square black chip U3.