Most likely the transistors or IC's in the output stage are burned.
As suggested earlier, contact the vendor. I am pretty sure it can be repaired, as long as the processor still works OK (and this seems to be the case with yours).
If not, then contact North Group from Nainjing (manufacturer, contact person is Gilman - it is ~200US$ to replace the whole controller and motors).
See here:
http://northgroup.en.made-in-china.c...ope-Mount.html