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I recieved a crazyflie nano as a christmas gift, and just took the time to solder it up today. It was flying perfectly fine for roughly two hours until the M4 motor started to spin even while the board was powered off. The motor does not spin when connected to USB without the battery, but will spin continuously when both are connected, even after the battery is removed. If thrust is given after disconnecting the battery, but leaving USB connected, the motor stops.

I did a search, and the consensus seems to be that the mosfet went bad. I'd been charging and discharging pretty much since I put it together. I checked my solder job, and it doesn't seem that the pad shorted to the nearby ground pad either. I contacted Seeed and am waiting for a reply, but I'm wondering if there could be any other issue. I had to contact Seeed through customer support because I didn't have an order number, not sure if that affects anything.

If I'm stuck fixing it, can I have some suggestions for alternative MOSFETs? NXP has put the EoL out for the current one. It looks like mouser has these available, but they're out of stock on digi-key, so we'll probably need an easy to source alternative for the community anyways.

The person who gave it to me explicitly said "Try not to break it the first day." Irony at its finest.

As you already suggested it is most likely a broken MOSFET. The replacement MOSFET is the PMV30UN. Keep us updated about the progress.

The motors are connected to the battery supply so that is why it spins when the battery is connected and the MOSFET is broken. The charger circuit is also connected to the battery supply and when you connect the USB you can fool the charging circuit that there is a battery that needs charging and it will then supply the motor with power to make it run.

Was the part number changed between revisions, or is this the "next best thing" so to speak? The wiki mentions the PMV31XN which has slightly higher tolerances across the board based on the datasheets.

EDIT: I checked the PMV30UN on DigiKey, and it's not just EoL, but marked obsolete. Does this mean the crazyflie is going to be unrepairable soon due to the lack of suitable mosfets?

I checked NXP website and they actually have the PMV30UN2 as replacement now. The difference between these MOSFETs are very small and the new ones actually have a little less RdsOn resistance, which is good. You will not notice any difference using PMV30UN or PMV30UN2 as a replacement.