I have a Humminbird Legend 2000 Deep(made by Zercom) that had the same problem. Mine was in warranty when it happened and they "fixed" it. It worked for two days. I finally took it apart and found the problem. There is no support for the main circuit board and after several cycles of the power switch, the board moves back in the housing and then the power button no longer makes proper contact. I actually had mine get stuck on! I cut a few small pieces of thin wood, glued them in, in strategic places...no more problems since then...3 yrs ago. Hope this helps.
Not sure what the value of the unit is, but in some instances, Its just better to by a new unit due to the repair costs.
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