The AS SIDB Y Cable used with previous core series HB units will not work with MEGA units (there is no DI channel in the AS SIDB Y Cable) ...
MEGA units need the 9 M SIDB Y cable ...
https://www.humminbird.com/Products/9-M-SIDB-Y/
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You do not lose CHIRP by using any of the HB Y cables ... CHIRP is a function of the head unit - and will CHIRP any xducer attached ...
Rickie