Is he standing in the purple circle?
edit: Assuming he has moved out of the purple, he needs to be topped off and not have Savage Wounding on him.
I'm thinking Savage Wounding might be the culprit as well. And no, he is not standing a purple circle...when our powertech goes down, it's right after "Gift of the Masters" (massive AoE pull in) and before the first "Breath of the Masters".
Perhaps it would be a better idea to just have our tanks swap during his "jumping phases" so that when he does "Gift of the Masters", our tanks are almost topped off.