depth finder problem

[dbell]

I have an '06 220 Select with the Smartcraft gauges. The depth finder just starting giving trouble. It will work fine for 15 minutes when we launch it and then read "_._" The little icon with the boat with waves under it is still there. I can shut the boat off while we're in a cove and when I start it up, the depth will read for a minute of so then go back to the _._ . I would appreciate any help or ideas.
Thanks