In Cura when I try to move the print head down from home in manual mode it does not respond. Printer will home and will move in x and y from home but not z.
If it homes up to the top of the machine then your RAMBo is probably damaged. Try turning both Z drive rods counter clockwise 3-4 full turns and see if it goes up and hits the upper limit and stops. If so then preform a end stop status check M119 and see what the results of that are in the control window log area.
Problem solved (I think). I was using the Lulzbot version of Cura that came on the USB drive of this Mini I bought on Ebay. So I tied Simplfy3d instead and with it had full control of x,y and z going into “jog controls” So then I thought I would delete Cura and reinstall it. When I reinstalled Cura wouldn’t even boot up. I think Its a compatibility problem with the latest beta of MacOS High Sierra. In any case Simplify3d works fine.