Motor running while off

[crazyTony]

I have just assembled my Crazyflie Nano.

Motor M2 comes on full speed as soon as the battery is plugged in.

Other observations:
- does not connect when battery only is plugged in
- when USB cable plugged in while battery is plugged in:
* M2 on at full speed
* radio connects
* motors M1 & M4 appear to operate as input is applied
* M3 does not come on

[poizone]

I had the same problem on my M4 motor. See: http://forum.bitcraze.se/viewtopic.php?f=5&t=1283

Contact Seeedstudio about replacement mosfets or having them repair it. You can also purchase new mosfets. The part number from the wiki is PMV31XN, and an alternate option is PMV30UN. Both of these are End of Life products, meaning availability may be spotty. The best choice would be the PMV30UN2, the replacement for the PMV30UN. The PMV30UN2 is only available from an Asian supplier so far, with a minimum order of 3000. Mouser has the PMV31XN and PMV30UN still. If you don't replace with the same MOSFET, be sure to replace all four so they're balanced.

EDIT: Saw you weren't getting anything from M3. Check that solder job for any shorts, because a motor not spinning is harder to diagnose. The MOSFETs are connected to the battery plane, so when one burns out it simply gets stuck ON, leading to constant power to that motor. I would honestly try to get the solder off the M3 pads with some braid and then redo it, just in case.