I have a 522c and a 510c and my picture is great. I'm not a bass fisherman anymore so I fish in water deeper than just enough to float the boat.:lol: I have clear deplictions of fish and bottom great color. The GPS and other functions are great.
The Lowrance 500c is a portable GPS navigator for your car. Are you perhaps talking about an LMS-520? If so, try doing a soft reset to get everything back to factory defaults then go from there. I can't remember how to do it but the instructs for hard and soft reset are on the Lowrance forum at BassBoatCentral.