So, I am embarrassed to post this. Are there diagnostics I can do on a Pi? I was booting up my Pi 3B+ with a 2 amp USB power supply (yes, not a 2.5 amp recommended by raspberrypi.org for the 3B+). I was getting the tell-tale lightning bolt in the corner, the command line complained about under-voltage. Did I take heed? Ummmm, no. But that may not be what caused my problem. Curiosity killed the cat. I wanted to know at what voltage the under=voltage message appeared. I poked around on pin 2 with my Fluke meter to monitor it. And, suddenly, everything shut down. Reboot didn’t cure it. Left it for an hour, still dead. It’s not a bad SD card (i’ve killed a few of those, different topic), because I had already converted the Pi 3B+ to USB boot, using a thumb drive with Raspbian. That thumb drive works fine in my other Pi 3. I get the red LED when I apply power, but nothing else happens.
Anything I can do to revive my Pi?