Old Lowrance 3400 depth finder
 

My ol Lowerence depth finder started flashing '0" today. The buttons work but it won't display the depth. Doesn't matter if I'm anchored or on plane. Engs running or not.
Hoping I don't have to mess with the transducer since I'll have to pull an eng to access it. Is there an easy fix for this? I'm having a hard time finding any Lowrance replacement that will fit in the 3 inch round hole.
Here's a pic from a old post:
https://www.offshoreonly.com/forums/...nder-quit.html

Thx!