I have over 1/2 dozen Metz 60's and have had this problem a couple of times over the years. It's always the power pack. Not sure how to fix the actual fault in the pack but second hand power packs are fairly cheap so I haven't worried about it too much. Just get another power pack. The CT1/2 packs work just fine on the CT4 heads. I mix and match without worrying about it.