Could be anything from a loose connector, a blown fuse, a bad display*or a significant failure in the transmitter.* Transmitter repair would entail removing the antenna (where the transmitter resides) and sending it to Raymarine for their flat rate repair service.* Here's their out of warranty repair page:
If you buy the boat then the first thing to do is to check cables, fuses and reseat any circuit boards inside the antenna housing.* Many times it can be as simple as reseating or cleaning a connection.* You will also need to determine if the unit is not transmitting or if the display is not functioning (two different faults).*
Alternatively, you may want to consider upgrading to a new, integrated chart plotter with overlaid radar or a new color radar.