Are you sure it’s the RPi and not the SD card?
Yep. I tried re-seating it in the old RPi, that had no effect. I tried the card from my other RPi (with wheezy) in the dead RPi. I read the sprinkler card in my reader on my computer with no problems, and the backup RPi is now running with that same card. It is a class 10 Sandisk 8 GB (I think).