Hi,
Usually blackening of a part of screen is most probably due to faulty LCD screen.
he Display of a GPS Consists of (2) Separate Devices that Work Together.
# The Liquid Crystal Display (LCD)
# The Touchscreen with Glass
The touchscreen consists of several transparent layers with spacers that are applied with an adhesive to a thin pane of glass. The touchscreen & glass lies on top of the LCD display. The touchscreen & LCD display both have their own flex cables that connect to the main board.
The touch screen has a ribbon flex cable with 4 or more conductors, each conductor representing a direction such as:
1. X-Coordinate, Left
2. X-Coordinate, Right
3. Y-Coordinate, Up
4. Y-Coordinate, Down
Most GPS units use a resistive, analog touchscreen. A voltage is applied to the touchscreen and by pressing anywhere on the touchscreen, it acts like a voltage divider, returning a specific voltage value, based upon the location touched on the screen. The GPS is programmed to read this voltage and it translates it back to a specific position on the screen, which may or may not activate a function.
The touchscreen doesn't have to sit directly on top of the display. If you were able to set it beside the display, you could still press the touchscreen and activate a function. The LCD display has no idea where the touchscreen is mounted, all it is concerned about, is what area is being pressed and whether or not that location matches a particular function on the LCD display menu.
Let me know,if needed further assistance.
Hope i helped you.
Thanks for using ' Fixya ' and have a nice day!!
Hope you have the manual..If not, please feel free to download from the below link:
http://www.navmanmarine.net/Navman/Templates/standardcontent.aspx?id=6356