Hitec 5995 servo winch issue

[ecoli]

So I went through the process of modding a Hitec 5995TG into a winch and have run into an issue. Did the basic mods, but now am finding that it will spin in one direction only and sit at neutral. If I fiddle with the self centering pot, I can make it spin in the other direction, so it's not like it's jammed or something. Tried out another servo winch and it works just fine. Not sure if it's got something to do with it being digital or if I'm missing something obvious. Any ideas?

Running a DX3r (and yes, the Aux switch is set to 3p) and just powering it through a 4AA battery pack.