I have just received an Arduino Yun rev. 2 as a replacement for my original one. The first board was sent back because it would not power up when plugged into a PC with its USB A port. It initally worked for a minute or two, but then stopped. The board still worked fine when powered from an old cellphone charger on its microusb port.
I ran the new board initially using power on its microusb port and it worked fine. Then I plugged its USB A port onto a USB A port onto my Windows 7 PC and it kept working. But I was unable to see any new USB device on the PC. Then I turned off the power on the microusb port, and it kept working, obviously getting power from the USB A port. But still I could not find any new USB device on the PC. So I unplugged it from the PC USB port and plugged it into an older PC running Ubuntu 16.04, using the USB A port. For a minute or so it powered up and seemed to be initialising normally, so I went to my Windows PC and connected via SSH to the Ubuntu box and ran lsusb. There was again no new USB device listed. So I went back to the Yun and by the time I got there, the Yun no longer had power (its LEDs were all off), and I noticed a smell around the Yun typical of a blown capacitor. So it looks like the USB A port has died. I unlugged the USB A port and plugged in power on the microusb port, and the board again worked fine.
I am guessing that the same thing happened to the original board - it worked for a short while using power from the USB A port, then that port died. The second board worked longer from its USB A port, but then that also died. So does anyone have any idea why this should be happening? The USB A ports on my PCs are nothing special, and are working fine with other devices. I did have to buy a USB A to USB A cable to plug the Yun rev. 2 in, but that should not be able to cause a problem like this, should it? Has anyone else had a problem like this?
In case it makes any difference, both the Yun rev. 2 boards were bought from Element14.