USB not working after wiping SD Card

Question

I've recently re-flashed my Pi, wiped the whole lot and put 'NOOBS_LITE_V2_4'. After plugging it back in, it powers up correctly, i get to the Noobs installation screen but the USB ports don't seem to work at all! So i cant install 'LibreELEC' because theres no power to to my keyboard.

I used to use my phone to control the Pi - but since wiping i cant do that either.

Anybody know why this would be happening, or if theres a way to tell if the ports are dead or just has the wrong software installed?

Any help is appreciated, cheers guys.

jlangbridge · Answer

That is indeed how they work. A USB port can supply a small amount of current, and depending on the device that has the USB port, this value changes. The Raspberry Pi can't deliver much (actually, there were stories of simple USB keys that would make the Pi reboot when inserted due to power drain). If a device pulls too much power, it is simply deactivated, which might be the case here. If your keyboard is pulling too much power, then the RPi shuts it down, and nothing works. By plugging in a powered USB hub, the Pi doesn't actually need to supply any energy, so everything connected to the hub, and powered by the hub, should be visible.

I'm not too sure how to debug your situation. I have a wireless keyboard/mouse combo that I use for my RPis, and I've never had a problem. I have had the USB key problem (which is a long story), so I know from experience that RPis can be a bit tricky, but a standard keyboard (not a flashy model with RGB LEDs) should work... Do you have a multimeter, or some way to test if the USB port is powered?

clem57 · Answer

Go to a powered hub which can be had for a few $$$.

rew · Answer

Small addition: The pi 1 has a sort-of-fuse in the USB that shuts off stuff when it draws too much power. IIRC this worked shitty and was removed quite quickly. So it might have been: "early raspberry pi 1 boards"....

The latest pi 3 has a dedicated chip arranging power for the USB ports. It powers up the USB port only after booting, and the chip will monitor the port for too much power and shut it down if that happens. I'm not entirely sure what the pi2 has.

(I have a many-port powered hub (15A power supply... plenty!), which I use to distribute power to several pi's on my desk. One of them is the "master" of all the other devices in that hub. So it has one cable for power, and the other from the USB port on the pi to the input port on the hub.... So when I unplug the pi's power because it needs to be powered down... it stays up. The hub will back-feed the pi. But when I unplug the input to the hub, the pi shuts down and doesn't come back up when I reconnect the USB-output-to-hub-input cable. It needs the power cable for a few seconds to enable the downstream USB ports....)