I'm upgrading an R2 with a Ramps 1.6+/mega2560 set at 24v. The Z axis A4988 board burned out but not the others. I had tweeked the steps_per_axis with no effect. I tried several different version of the firmware but they all left the Z axis a4988 too hot. Any ideas about why only the z axis a4988 board would be too hot. is it likely something with the ramps 1.6+board on 24 v or in the firmware. Thanks for your help.