If the test firmware is cycling the colors properly (red, green, blue, and white) then the pic and regulators have to be working properly. That leaves the DMX parts...
try swapping the 485 chip with another device
Verify the orange/white-orange wires are not reversed
Check to make sure only the last item in the dmx chain is terminated
Do all of this with the heat sink outside the case. If the behavior changes when you put the heat sink in the case, something is shorting to the case...
If the test software gives you yellow, green, cyan, white, then the green channel is shorting to the case...