Lowrance hds7 gen 1 Sonar not working. Help!!

Hello! My depth finder randomly stopped reading depths. The gps portion still works fine but sonar portion only reads 0 feet. This is a boat I bought this year and I didn't install the transducer. I'm guessing it is installed as a through hull transducer bc I don't see a transducer on the outside of the boat.

I'm thinking of installing a transom transducer myself to see if that is the issue. Any thoughts on how to troubleshoot this?

Also - anyone in the Austin area do work on the side to help fellers like me out? Don't gave a month to wait to put it in the shop if I can't figure it out.