I have a 898 that has GPS, SI, DI and traditional down sonar. Plus LAKEMASTER CHIP which I love( yes love)! I think my unit is dying...you have to turn it on about 4-5 times before it is warmed enough to stay on. I don't know the difference between Mega & Helix!! What model and systems to I buy to get back to where I am with 898? Anybody got a good 898 they would like to sell? Thanks for the help!