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[np77]

Hello!
I have just recieved two devices and with both i have the same problem. It works badly with alimentation via micro usb. Even only with ethernet between TP1 and TP2 i have less than 4 volts. But if i connect powered usb hub to usb port it works good even without power via microusb. And between TP1 and TP2 there is about 5 volts. Is there any solution of this problem?
With best regards,
Nikolay

[Roger]

The Pi requires a power supply that will provide 5 volts at at least 750 milliamps.  Some inexpensive PSUs that claim to be 5V/1A actually drop voltage as more current is drawn - if you're getting 4V between the test points then your PSU is probably to blame.  As for the Pi being backpowered by the powered hub, there is nothing much that can be done about it.  It seems to be (sad to say) a problem that is associated with the more inexpensive sort of powered hub.  The question was debated at some length on the Pi forum (www.raspberrypi.org) and as far as I remember, the general consensus was that powering the Pi in that way "might" damage the Pi;  one of the solutions was to open the USB hub and cut the +5V wire to the USB connector.   I'd only recommend that if you know exactly what you're doing!