I just recently sent my Lowrance 520c off to lowrance for service because it locked up and the keys quit working. On receipt of the fixed unit they included a new power cord in the box and said that was the root of my problem. I changed out the power cords and the problem seemd to be repaired until i inserted by hot maps plus card into it. Then, it locked up and did what it was doing before i sent it off. Is anyone else familiar with these products? Is it the card thats causing the problem?