I don't know why it does that, but I did find a work around.  Go under your printer shape in repetier.  The bed left and bed front fields under printer settings will take negative values, so I took a guess and set them each to -40 and printed a 20mm calibration cube.  Doing a little math we can see that the edges of the cube should be 65mm from the edge of the bed.  After printing but before removing the part from the bed, I took out the calipers and measured the actual distance that I was getting.  Doing a little more math, I found that setting both of those fields to -57 results in the cube printing in damn near the middle of the bed (I centered the print).

Since the SD4 bed is 50 mm bigger, I would try that test with your values set to -107 and see if that calibration cube lands in the center of your bed.  Like I said, I don't know why it does that, but I just found a work around for now.  The downside is that under manual controls, where it shows your object being created in real time, it will only show the part of the bed that is >0, so you essentially lose the cool graphic of watching the part being built on your screen.

Let me know if you find a better way to fix it.

I recently upgraded to a Rumba board with Marlin firmware (copied from SD4 configuration except for motherboard selection and E3D extruder changes) and my prints, no matter where I locate and slice them, always print in the back right corner (max x and y.)  Z works fine

I know of 3 places where you need to specify axis values:

-Marlin config.h (min 0, max 200) on x and y
-Slic3r (200x200 x and y, bed center at 100,100)
-Repetier host printer settings (front left at 0,0)

Is there some location that I'm missing?  I suspect its a marlin issue as I've explored repetier and slic3r pretty thoroughly.  As far as I can tell my Marlin configuration is the same as SD4, but is there something that default Marlin has set up incorrectly for SD4?

Any help would be appreciated!
Greg