Garmin screen brightness problem

I have an older Garmin Echomap Chirp 94sv chartplotter/sonar unit. To adjust the screen brightness, you simply push the power button to cycle through the different levels of brightness. But for some reason when I try to change the level it cycles from 100%, to 90%, to a black screen, then back to 100%, and so forth. Anybody run into this before? Would updating the software or returning the unit to factory settings be wise? Is there a downside to that approach?