i have a sa 250, with the perkins and have noticed that the machine doesnt want to weld when the fine current adjustment is at about 25 or lower regardless of where the current range selector is set.  when i say it doesnt want to weld i mean that i get spark but you can tell the amperage is way low.
for example when using an 1/8 7018 and the current range selector is in the 120-190 position and the fine current adjustment is at anything below 25, it wont weld (way to cold)
as long as your on the upper end of the fine range it works great, everything else works perfectly too, i have checked the fine current reheostat by measuring the ocv, and its fine.
anyone had this problem before ?  or are the models just like this?, just doesnt seem right to me