Marine Electronics Questions? Ask a Technician for Answers ASAP
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The first thing to check internally to the Humminbird device is, the power plug and its connections/joints to the board inside. If the power cord is yanked on at any time, those connections can (eventually) crack.
If the device is hooked up with a removable power connection (I should hope) can you try another device on the same power connection? it's dubious, but it might illustrate where the problem is for sure (and it's almost surely inside the device.)