Power for extra fan



I've got OnStep running already on a Fysect S6 and I'm working on a case for it now. I have a small fan laying around and I thought I could use it for this build, but I know little about electronics in general so I'm wondering: is it OK to draw some power from one of the unused connectors in this board?
I read in the wiki that fans are not supported, but I'm guessing this means "you can't control them", and I just want it to be always on. It is a 12v 0.16A fan but I don't want it to run on full speed, so connecting it to a 12v line is not an option. I tested it with 5v on the port labeled as "E0-DIAG" and it works perfectly but, is this safe or I'll fry the board at some point? Also I've no idea whether or how this interacts with the motors (it's called E0 after all). Would the EXP1 or EXP2 ports be a better option?




This should not be an issue.  Your fan may not operate with as high as an RPM as designed, but you seem to be OK with that.  As long as you are not using the E0 Diag slot with a stepper driver, taking the 5V from there should be no different than taking it from EXP1 or EXP2.