ST60 Depth Issue

[NeilB]

Chuck,
Purchased the new depth transducer and tested, nothing changed,
eliminating the possibility of transducer failure. Have not been able to
eliminate the ST60 Depth as purchased the i50 but over my experience to install.
Meantime with all the plugging and unplugging the C120 is not coming on and off repeatedly by itself. First the C120 screen came on for 3-5 minutes and then went off and immediately came on as if rebooting.
I finally unplugged power from back, then plugged back, reset to factory default settings on menu and it stayed on and seemed ok. In fact the depth and everything appeared to be working fine. Left on 2-3 hours with no issue. That was a week ago. Yesterday I was working on a non electric item at the boat so I turned on electronics and left them on while I worked. They worked perfect, no problem. Left them on all night. When I returned to boat this morning the C120 was turning itself on and off, this time at 3 second intervals. Also the depth was reading up and down.
I held the power button down but the C120 unit would not power down, just continued to show screen on then off. I had to unplug from back to power down. I still have been unable to get any tech to return calls. There is no field service in this area for Raymarine. Very disturbing. If I had not already sold my Navpod for my RL70C I would just re-install it.
Any ideas what is going on. Could it be a faulty SeaTalk? I just don't know where to turn. One Electronics guy I talked to said he was booked for 10 months out. Sad