I am in a similar situation - interface won't connect to PC and upon inspection there is discolouration at this same D1. I have attached photos I have taken for your reference.
[image|3302417]
Although I suspect this diode is defective I did some continuity tests captured here in this image:
[image|3302418]
[br]
[br]
I too am trying to identify and replace this diode so if you have any luck please let me know too!