Hey there, :) a friend of mine is trying to do the black armory quest line to get Izanagis burden. She has already completed the quest steps of the first 2 forges but the vex transponder which is needed to unlock the third forge is not dropping for her. We already made sure that she is on the right character and yes she is also killing the vex on nessus. And we made sure that she has got free quest space in her inventory. Is there any other advice or tips you could give ? Because I did the quest nearly a year ago and don't remember having any problems.
All forges are now automatically unlocked. You don't need to do the legacy missions to unlock them. The forges rotate daily. You can access the current forge by visiting the EDZ map, and selecting it.