Quite a few people are seeing a variety of USB problems - some of these might be related to insufficient voltage on USB devices due to drops along lead, connector and internal fuses on the Pi. There's a long discussion about these issues (192 posts) in the Feedback and Requests forum, under "Design ...

OK, some actual measurements breaking into the USB leads (ambient temp 25C, a nice warm day up here in Newcastle) USB PSU (iPad) off load 5.18v on (Pi) load 4.96v This drops to 4.82v at the Pi itself, then 4.68v after going through F3. USB keyboard (Logitech K120) and mouse (IT works MCO 05, quiesce...

I've measured (accurately) F3 on two Raspi - 0.2 and 0.3 ohms, so I agree F3 won't be a problem if current draws are kept within spec. After popping F1 it returned back down to about 4 ohms when the Raspi had completely cooled down. So, they are doing the job as intended - just that they can throw u...

I should have posted I was using the Raspi "headless" i.e. without keyboard/mouse/monitor having previously set up SSH and a web server on it, so the USB memory stick was the only USB device plugged in. BTW the polyfuse didn't pop immediately, just after a couple of minutes. I agree with other posts...

Just found this post after popping the F1 polyfuse with a Kingston DataTraveller USB memory stick. I hadn't expected any problems using a memory stick to transfer data to/from the Pi :cry: BTW I measured the remaining polyfuse - it's 5 ohms. Such low current polyfuses at least rate a clear warning f...