Zercom was bought out by Humminbird.The Zercom I have is now called the Hunninbird HDR 610.You can check to see if yours is the same by looking at the picture in an Overtons catalogue or by going to their website.To print or look at a manual,go to Humminbird.com and put your mouse on "support".Go to the right and click on "product manuals".Almost at the bottom of the page,you will find "HDR Series" and click on HDR 600.Hope this helps.BTW,turns out that mine doesn't work.The instrument seems fine.I believe the transducer is not(but I really don't know).If you want these parts,I'd be happy to give them to ya.