It could be just a simple setting, like someone has turned on "Monitor mode" by mistake in the radar setup. It is very likely that the radar can be repaired but depends on the problem and the radar you are talking about. Same goes for cost. I would say the NavNet series one (2002) is done as a chart plotter because you can't buy maps for them anymore. If you using only as a radar it can still have many years left depending on condition. If plotter is needed, I would recommend replacing the RDP139 for a good used RDP149 (Vx2) that you can still buy C-map charts for. Have you called into tech support to see if the radar might be in monitor or simulation mode?