I have a raymarine c80 chartplotter onbaoard.It boots up fine,with all functions working.After a half an hour or so,the screen goes to verticle grey lines with no functions working.Rebooting at that time has no positive effect.When I come down the following weekend,the unit will go thru the same procedure.Is it the chartplotter that needs servicing,the microchip,or the gps antennae?Any help would be appreciated.Thanking in advance