Mapping fishfinders

[RIKen822]

It looks like my 20 year old Hummingbird fish finder has died. It reads around 420 ft even though I'm in about 10-50 feet of water. Head unit and transducer pass built-in diagnostics.

I'm considering buying a $300 mapping fish finder. I've really only used my old finder as a depth sensor. Since I'd prefer to not haul the boat to install a new transom transducer, any thoughts as to if the mapping capabilities are good enough to give my a rough idea of my depth? If so, I figure that I can mount the transducer in the fall.

Thoughts?

Any suggestions on how to resurrect from the depth my old unit?

Thanks