When I turn the boat main power switch on my LMS 520 comes on? The last tournament I fished it rained all day so I am assuming it has something to do with water somewhere??? Any ideas? Also my LCX27c was full of water, was this a problem with this model? I have taken it apart to dry and see if I can get it working again.
Sounds like something in the software more than the hardware when it comes to your 520 bud. Try a Hard reset after saving all of your waypoints to a card. When the unit is off hold zoom in, zoom out, and power until the basemap appears on the screen and let go of the buttons. Does it come right back on after you turn it off on its own?
Like all Lowrance units, they are rated to be waterproof, but sometimes in extreme rain or constant rain, the units get water in them. Taking it apart and drying it out is probably the best thing to do for that unit.
I would guess the issue lies more with your on/off button, as that is the only place where the power circuit can close and make it power up. Try pressing and releasing it several times. Fairly common for those to go bad I'm afraid. I would bank that it will soon either not come on, or it will start going off when you do not want it to. Many/many of those and similar models have had to be fixed, by installing momentary switches in place of the power button. Without getting into the reason why, just start with using the button jiggling method. This is simply my 2cents! Maybe the reason!