Howard Nurse, W6HN
I don't blame you for being discouraged, but I have 100% confidence we can get the 857 going.
I'm not clear on why disconnecting the mic would be related to the report of an unknown error...
Let's back up a minute on the mic. You are connecting RigPi audio through the rear DATA connector on your radio. That DATA connector has a audio input that should come from RigPi. It also has a PTT connection. The PTT connection switches the audio input from the mic to the DATA connector. This is done so the radio won't pick up mic noise when you are using the DATA connector as an audio source. Since the current problem is no transmit audio, one possible cause is that the DATA PTT connection isn't switching the audio. My proposed test was to put the radio into SSB transmit from RigPi, then key the mic to see if audio is still getting through that path. If it is, then that narrows the problem.