Source 4wrd "off"

I have a good stock of Source 4wrd's in my inventory and one of them is giving me trouble. When I go direct to full it stays on for about 2 second and then turns off. The LED shows "OFF". If I go to 99% and then wheel up it stays on no problem. It's the first in a DMX line of 12 Source 4wrds (which is terminated) and is the only one out of a rig of 50 that this happens to.