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Theros

I had sent this unit in because it was not recognizing the depth sounder and it came back working. Since then it continually jumps all over the chart when I am using it. It will ask if I want to change course. The boat icon jumps all over the screen. The chart will change from the view I want to maximum view at any time. In effect, the touch screen is either unusable or it is jumping all over the place. I is acting like it is possessed if that makes any sense. Is there anything I can do to make this better. I am sailing around the world, cannot go without one again. I need this plotter to work and be consistent. What can you do for me?