Furuno 1724 radar image size

[Mickeyrouse]

I have what I hope is a set-up/adjustment problem on our Furuno 1724 radar/plotter. The operators manual doesn’t seem to address the problem. This is a dis-continued system, and Furuno doesn’t seem to be interested in discussing it.
The chart plotter works fine: charts appear as expected, range zooms in and out as expected, when used with FAS-50 AIS targets display appropriate data, etc,etc. Plotter performs okay.
However, when I switch to radar display, the image size of the swept area is so small as to be useless: approximately 3/8” in diameter. The rest of the screen is white. The range circles respond as requested on the range increase/decrease buttons, but the radar image remains at thumbnail size. The radome is obviously sweeping, because the intensity of the colors change in a sweep style, meaning a bright area that progressively dims in a sweep fashion until a rotating radius line suddenly brightens. It’s just too small to be useable.
So: can I do anything about this? And how?