My fear of having to pay for a potentially expensive repair motivated me to learn all I could to isolate the possible cause of the malfunction. Bottom line was there was a cable end that wasn’t fully seated. It runs from the CSP (central signal processor -the brains) to the PS (power supply unit). I’m a very happy camper as they say. No need to read further unless you’re interested in some of the specifics of the journey.
I found a PDF copy of “Disklavier IV/Pro Series Maintenance Handbook” online and it included some post delivery checks as well as some field servicing info. I learned that one could access the Service Center app on the PRC100 pocket controller that interfaces with the Disklavier. And there is a Maintenance Mode one can enter with a key sequence.
Long story short, not being able to “read” info that’s resident in the CSP, nor initiate any “piano response” that gets the solenoids to “play” keys nor move the pedals, I feared that the CSP was faulty. Again, worrying about how much a professional diagnosis and CSP repair (or replacement) could set us back, I crawled under the piano again and inspected the ends of every cable that plugged into it. That’s when I found the loose connection at the PS end. Yes! Now everything works!