When I plug in my keyboard's bluetooth dongle to the USB port, my Raspberry Pi boots up. When I take it out, the power seems to instantly cut (screen goes black, Pi unreachable by ping/ssh). Note that this is the opposite of the normal not-enough-power situation - again, having the USB device plugged in seems to enable the power, rather than draw too much. This does not happen every time (last time the Pi did not have the device attached it was up for ~250 days) but is very frequent.

What could be causing this?

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This is an acknowledged defect of the A/B models that is corrected in the +/2 models. When you connect certain things to the USB ports -- a common culprit is wifi adapters -- there is a current surge and corresponding voltage drop (power = voltage * current, or voltage = power / current) which causes the pi to reboot.

Unfortunately you need to have such things attached when you boot. In my experience removing them is okay.

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  • This sounds related but not exactly right - my Pi goes off on removal (and stays off, so probably not momentary disconnect/reconnect -> reboot). Any link to further info? – Sam Brightman Jan 14 '16 at 14:08
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    raspberrypi.org/forums/viewtopic.php?f=28&t=17611 I can't say that removing them won't do it, just that I don't recall that happening to me (but I usually leave such stuff attached). To speculate, it could be that removing them may cause a quick off/on/off event. – goldilocks Jan 14 '16 at 14:13
  • I would not bother getting too into the solutions contemplated in that (3+ year old) thread -- I don't think any of them work (better power supply, etc) and the problem could not be solved without changing circuitry on the board. – goldilocks Jan 14 '16 at 14:15
  • Marking as accepting for now, seems sufficiently closely related unless someone else has a better answer. – Sam Brightman Jan 14 '16 at 14:23
  • Someone out there certainly understands this in better detail; I've never even tried to read the schematics. – goldilocks Jan 14 '16 at 14:25

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