My 1621 mark 2 radar will only show images/ targets on the display only when the range is zoomed out 1 mile or greater. Even if the target is closer than 1 mile. When I see a target with in the 1 mile outer ring, I decrease the range less than 1 mile and the display is blank. Has anyone had this issue? I’m just curious if it’s the display, cable, or bad magnetron?