Darth Sion

ok im on the Ravenger and ive killed "Darth Nihlus" and taken his mask, ive set 3 of 4 mines, kex told me to find a new bomb after his blew up, so found the new fourth bomb and where to put it but the bomb wont set like the others with a video or anything... i know i have it, but ive been to every place i have to set a mine like 25 or 30 times "no joke" and nothing will happen please help me!! P.S. i dont know if its important or not but im on the "Dark Side"