I must be the unluckiest person in the world my new Humminbird 899ci HD SI unit was bought 1/31/2016 and was made in 05/14/2014. I should have known something like this when I had to update the unit from 6.900 to 7.650. By reading and looking at the dates of the posts mine was made about this time frame when the units were having trouble. Well the only way I will be able to know for sure is to just try it and see if it will works on 800 khz.