The ones in broken valley are all turned off by activating a lever on on some kind of machine.
if you did some you know what to look for, you must have missed one. Check in all those little walled in areas.
Just fly over and you should be able to see the machines, drop in and see if you can flip the lever.
Make sure to use the various teleporters as well. I think there might be one lever that you can only get to by teleporter. Did you do that one?
