I've been battling my new 3DR Y6B for 2 days. One motor wouldn't start up. Found that problem, I had the wire from the ESC plugged in upside down. Now that motor was working, but another motor was dead !!!
I remembered reading somewhere on this forum, about a bad connection on the power distribution board. Got out my multimeter, and sure enough, on the underside of the PDB, (+ side), I had no contact. Rather than take the top plate back off, I just soldered that ESC hot wire, to the positive terminal on the PDB. "IT LIVES" However I'm concerned about the rest of the connections on that board. It was VERY hard to plug in the Deans connectors to the board, and perhaps that led to a broke solder joint. I'll make her fly for a little bit, just to know "I WON", then maybe break it back down and re-do that PDB setup.