New Zealand Vintage Computer Forums

I have this old Apple CRT mono-chrome monitor.
When plugged into a Macintosh LC II, the image is stable and clear.
When plugged into another Macintosh LC III, the image is vertically unstable, i.e., the image moves very quickly from top to bottom, without moving beyond the screen edges.
Any ideas of what can be the problem and how I can fix it?

Is the LC III using a different vsync to the LC II? Could be that.