Dublin,
Try making a screen snapshot of what you are seeing.

You may also want to try:
- slowing the Chart Speed menu setting down. The arch may be there but is getting stretched out over a wider area.
- setting the SwitchFire menu to the Max Mode setting.
- the various Sonar Color menus settings as the arch may be there but you may not be able to see it due to the lighting conditions and the colors used for the weaker (outside edge) sonar returns.