I’ve been looking for a XI 1521 transducer to convert my Humminbird Helix over for ice fishing and they’re sold out everywhere. Someone had a used one for sale and said it was a 1521. There is nothing stating what transducer it is. There is a yellow plastic piece down towards the plug in and it has nothing on it. Also there is a white label wrapped around it with the numbers 181108870449 and also the number 490313-1. Is there anyway to identify this transducer? All the ice ducers look identical.