I purchased a TNC-PI a few years ago and it ended up on the shelf "for when I have more time".
Well, now I have more time, and I can't get it to work.
I have made all the configuration changes to raspbian for the serial port configuration.
The pitnc_get/setparams works fine.   I can even trigger the test tones to check deviation.
There is no data being decoded by "cat /dev/serial0(or ttyAMA0)" or by minicom or any other com program.
Could it be a blown MX-614?   Does it use the MX-614 to generate the test tones?    What handles the actual decoding?   Where do I start with this?