Is it a Furuno
? I had the exact same problem and on a model 1621 mk II radar. I sent it to the factory and they upgraded the software
and waived some magic sticks over it. Cost me $200 and everythign is working fine. My radar is a 1996 model and is working very well now.
Between us there was, as I have already said somewhere, the bond of the sea. Besides holding our hearts together through long periods of separation, it had the effect of making us tolerant of each other's yarns -- and even convictions. Heart of Darkness