ESC went up in smoke

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1

I was just hovering when one the motors on my 3DR quad cut out. I tried disarming and rearming and it wouldn’t spin. So then disarmed with the battery connected on my work bench I started checking wire connections, but didn’t see anything out of place. While I was looking up the ESC calibration procedure on my laptop, the motor that had cut out started to twitch a few times. Then smoke came out of the ESC and I unplugged the battery immediately. The other ESCs were all cool to the touch.

I cut off the shrink tube and one of the chips was clearly damaged. See attached picture.

Before I attach another ESC, is there something I might have done to smoke the ESC? I’ve gone through the initial setup steps including ESC calibration and had some very brief flights, but I’m still very green.

I’m using a Pixhawk autopilot with a 3DR power distribution board and the 20A ESCs from the 3DR store:
http://store.3drobotics.com/products/esc-20-amp-SimonK-1

PS: This forum software is too picky about images. I had to down sample my image and then rotate it after I got this error: “The image must be at least 0 pixels wide, 0 pixels high and at most 1024 pixels wide and 768 pixels high. The submitted image is 768 pixels wide and 1024 pixels high.”

2

The lower left chip is damaged has this ESC been in a crash?

3

What you see, is the result of both source and sink FET being closed at the same time, most likely, the most burnt FET lost its gate connection (the pin that have one pad for itself) and remained in last state, then the other came on, had lower internal resistance because it’s gate wasn’t floating, and shifted the circuit.
Seems like just a defective ESC.
But you can, if you want, check the motor for damaged windings. Run this motor at lowest rpm, no prop, and apply load by breaking the casing with a finger, the motor should have no problem starting after being stopped.
If it fails to resume from some position, it’s defective, art least one winding is broken.