Raymarine C80 Chartplotted with 300 DSM issue?

[Paulus]

Hi,

My Raymarine C80 "head unit" screen, only as part of the Fish Finder function, displays random multi-color scatter slowly moving across the screen, as if functional, while the digital depth reading is stuck on 7.2... at times flipping back and forth from 7.2 to 7.3 or 7.1ft.

The thru-hull sonar/transducer seems functional as I can hear its usual rapid ticking while powered on - it is connected to the binnacle mounted head unit, through a DSM 300 mounted inside near the Transducer.

The DSM, with the head unit on in Fish Finder mode, shows a solid "on" amber LED indication; that same LED flashes 2x amber with the head unit disconnected.

This condition suddenly appeared while otherwise functioning normal, last June 2017 - it has not reversed itself since then, even after powering up and down; disconnecting the DSM and re-connecting; conducting a factory reset at head unit; and my latest attempt to wake it back up by re-wiring all power connections to ensure full battery power (12.8V) is received at all components.

Everything else works just fine - Charts, Radar, GPS receiver...

With this, I am hoping someone can point me in the right direction to get the depth/finder unit up and running again.

Thanks,

Paulus
CAL 2-34
Perth Amboy, NJ