HB 998C SI screen freezes at depths less than 8 ft

I just purchased a 998c si unit and set it up per instructions. The unit works good in 10ft or more deph; but the screen freezes any time I get into water less than 8 ft. also the depth reading goes crazy recording 950ft to 450ft in a lake 18ft max depth. When this happens, I move to deeper water 10 to 12 ft and the unit recovers. I have contacted HB and they have sent replacemets for both the transducer, and the head and still the same problem. They are still reviewing photos I sent. This problem has been going on for a month. Does anyone have information on this type problem? Please help.

Do you have it linked to another unit? If so, they could be on a different frequency and messing each other up. Just a thought.

Thanks Super Do, No I have a very simple system, just the power, transducer and gps ant. connected to the head. I have run just the bow mount, and just drifting and it still has this problem. Humminbird has had my info since early May and say their techs are looking into the problem.

I live in Amasa, MI in the UP of Mich. Is there anyone near me that has a 998 that perhaps we could get together and compare components? I would drive to your location.

What version of software is in it?

When in shallow water go into the depth finder menu and turn off aaaaaaaaaa if I remember, I don`t have me unit handy I want to say switchfire. That may take care of the problem.