Nuvi 3590 with strange black marks on map, not screen as you can scroll around.

If these black marks were always on the same part of the screen I would say the LCD display (or the connectors to it) are damaged, however as they scroll around the screen I would say there is a block of memory that is corrupted and when the map tries to display that area then the black marks appear

If the map is held on microSD card then it may be that the corrupted memory is also on the microSD and downloading the map onto a new microSD will fix the problem, If the corrupted memory area is 'internal' then I think your only option is to try a full factory reset, but if the map is 'internal' then you could force the map to be written to a microSD card and remove the map from the corrupted 'internal' memory area



The bad news is that screen display memory is probably not the same as the memory that actually holds the map, it is more likely to be an area of internal RAM that is not replaceable, so if the factory reset / new microSD doesn't work the unit would need to be replaced