Port COM2 may not be the MBD; that was a guess based on similar timestamps, but the guess could definitely be wrong. Bottom line is, I still don't know what this port is.
The procedure I used to install the Chinese clone driver (for the CH340 chip) is here:
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http://www.instructables.com/id/How-to-fix-bad-Chinese-Arduino-clones/
The procedure includes a close-up picture of the chip.
I have only USB 2.0 - hopefully USB 3.0 will be supported in the future because it will become more prevalent
Today's troubleshooting and results:
- I installed IDE 1.8.5 on my wife's PC. I could successfully program the Arduino and monitor the Serial port.
- I took the Arduino back to my PC, and now it could program the Arduino and monitor the Serial port. Don't know how/why this fixed anything, but it appeared to do so.
- I reattached components for my application to the Arduino and attempted to load the application. Appeared to load, but the application didn't work.
- I replaced a HC-12 transceiver module that I had a hunch could be defective. Apparently it was, because now the application works.
Today's summary:
- I don't know what COM2 is, but it was there before the problem started and it's still there, maybe harmless
- I may have had multiple hardware issues, but especially the HC-12 transceiver could have been masking or at least confusing some of the problems. In addition, maybe hardware defects stressed polyfuses or other components that took awhile to heal?.
- I really don't know how the process I used healed anything, but it appears to have done so.
I really appreciate the feedback - it feels good to have your support.