Is it possible it’s this?
My Screen Turns On and Then Goes Dark
If your display turns on, shows the blue Lowrance screen, and then goes completely dark, most likely you have accidently shut your backlight off while powering off your unit.
To resolve this problem, once the unit is powered on and the screen is dark, simply press the “Power” button a few times until the screen brightens back up. Do not hold the “Power” button down, just quickly press and release the button.
To prevent this from happening again, when powering off your display, simply press the “Power” button one time and then select “Power Off.” This will save all settings and features and safely shut down your display.