My friend has a Lowrance 332c unit on his boat. Last year, the depth quit reading. It would just flash 60'. A couple days ago, he replaced the transducer, and it began working again. Today, it stopped working again. Any ideas??

A Louiseville slugger or a 357 magnum is where I would start

They have been known to have issues.  Try finding another head unit you can hook up and see how it works.  You can use just about any other newer Lowrance unit and even older X-125/135 or 520c etc.  That should tell you if it's the unit or transducer.

 

 Probably looking at getting a new unit though.  Lowrance no longer supports the 332c as far as I know so unless you can find somebody to repair it, new or good working used is your only option.