ACC Automatic Combustion Control, not working (North Star, Quadrafire, Consitution)

I have a North Star fireplace with the ACC feature(manufacture date Sept '08), it was working perfectly and I kinda liked it. (North star is very similar, same parent company as Quadrafire and the Heatlator Consitution). I would engage it, it would let the fire get really hot, then slowly choke it off to my set point.

But the other day, it seems to have just stopped working. I can watch as the main primary control linkage pulls the triangle like timer plate cam, and can hear the ticking of the timer The triangle plate cam pushes up on a piece of flat steel with a screw in the bottom of it (the screw that rides the moving timer plate cam), that flat steel goes staight up into a box I can't see into. The timer itself is working too, it slowly returns the timer cam plate back over the course of 45-60minutes or so.
It used to be, once engaged the primary control rod would have little effect on the fire for the first 45+ minutes or so. But now, when I move the primary rod back to where I want to set it, it chokes off the fire straight away, like the ACC just didn't engage.
What does that little flat piece that goes up hook to? I'm kinda ready to just take off the 2 7/16" bolts holding the assembly to the bottom of the fireplace to check it and see what I can see, but is there something specific I can check for? Thanks for any help.