Its failure was accompanied by very strange things so it may be the Pi Zero that failed (or both) rather than the AudioInjector.  I may have not taken adequate precautions against electrostatic shock to the boards.  

Specifically a set of commands to record the sound on one pi and send it via SSH and aplay it on another stopped working.   I could SSH (by wifi) into the first pi and could ping the second pi and even ssh from the first pi into the second pi so this was strange.  They are both on the same network with a unifi edgerouter with no intervening firewall so that wasn't the problem.

After several reboots ssh was working normally again but the sound on the pi zero was not..   dmesg shows a set of errors that seem to  relate to voltages not being present --using default regulator (or something like that) and there is no final  message saying the mapping is ok.  I cannot capture a sound file that has anything but silence in it even though I know the AI Zero board is getting appropriate input.   I also cannot get it to play anything to its output.  Nevertheless the aplay -l and arecord -l show entries for the audioinjector and it is the only soundcard in the system.  Alsa settings are what they were before.    Of course I did not look at the dmesg output when things were working so I don't know if this is really different.  

So either I did something to fry the pi or the board or the both, or in trying to fix the problem I updated the OS to a configuration that no longer works., 

I suppose I could start over with a fresh os install and see if that works but at this point I am guessing it is a hardware issue and the pi zero and the AI zero are inexpensive enough relative to my time (and my inadequae software skills)  that it's best to just try a fresh AI zero with a different raspberry pi before trying a new software install. 

Will keep this list posted on the results -- Only posting this now on the off chance someone else has had the same symptoms. 
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