Hi This is one that has a bad transistor on the main board, there are many on this one. It really need to be sent to Lowrance to have this fixed.
It is worth the cost of repair in this case.
I wish I had better news for you but I know this problem well after 30 years in marine electronics service.
Please visit : http://www.lowrance.com/en/
They can help set up the repair order ticket, they are excellent and usually not very expensive;-)
In any case, I will stick with you until this is complete.
Please rate my service kindly.
Also it is the only way I am credited for my time and expertise with you.
Once you rate, I will be notified and will add your question to my priority list so you can reach me anytime until this problem is solved.
Then you can reach me by simply replying to this message anytime.
Thank you and have a great day!