I have a helix 7 g2 and have had a similar problem with the down imaging cutting off past a certain depth. I called humminbird about it and they told me to do a factory reset, and to update the software. I havent yet updated the software, for one thing because I dont have a micro SD card reader. I did the factory reset and it didn't fix it. But I would try those 2 things and see if it helps. Does the 2d work past 40 feet down? For some reason my down imaging has that problem but the 2d doesnt.