I'm fairly new to Arduinos. What is a loop back test? How do I run it? What results should I expect?
In the meantime, I tried another board that used to work - a feather. It just locked up continuously on upload, of the ultra simple "Blink," so its beginning to look more & more like the IDE 1.8.5 may somehow may be corrupted. What do you think - should I delete it & start over with a fresh download?
Also, if you think this is the problem, please respond to my questions about the loop back test. I need to learn everything I can about Arduino IDE!
Many thanks for your help.