I hope this might help anyone who has the same problem updating their firmware. I'm going to go in reverse here, first describing what ultimately worked for me and then describing the symptom/problem.
- Instead of using WinZip or WinRAR to extract the .zip download, I simply used native Windows Explorer
- Instead of copying and pasting an extracted "PCBUFF" folder to the SD card, I dragged and dropped
the "PCBUFF" folder I saw (after letting Windows Explorer open the zip as described above) onto the SD card.
I don't know which of the two made the difference or if both did, but the firmware upgrade on my next Einstein went quickly and smootly and exactly as described.
What was happening before when I was using WinRAR or WinZip and copying
the "PCBUFF" folder to the SD card? I would insert the card into my Einstein, plug the power in, there would be a very quiet and brief "whirr" of power from the unit, and then nothing.
Before having success on my own as I described above, I ended up sending my first Einstein in thinking just maybe there was something wrong with it. The unit came back with a note that the tech loaded the firmware successfully from both his own card AND mine. That suggested pretty strongly there had to be something I was doing differently, and led me to extracting differently and putting the "PCBUFF" firmware upgrade folder onto the SD card differently.
Thank you to the PCB staff for their usual great customer service and for the quick turn around (9 days, door-to-door), and I hope the above information proves helpful to someone.