C-80 stopped displaying Data

I have an old C-80 which seems to be installed using a Seatalk conversion kit powered from the AutoPilot
The Tridata and ST60+ work and the AutoPilot display seems to be OK.
BUT None of the telemetry from and sensors (GPS, Wind, Depth) are being shown in the C-80 display. I've replaced the battery in the GPS antenna and remade all connections.

I'd like a technique to test the 3 wire (Seatalk 1??) at the C-80 connection or ANY other idea to help solve this problem.

Please see the attached file for some pictures of the equipment.
Thanks
Pat
Blue Skies
Portsmouth NH & Newport RI

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