I was working with a team which was experiencing problems with cortex smoking (luckily it has been resolved). Now that I think about it, I really don’t know what causes this problem, what doesn’t, and how to fix it. Anyone know the specifics?
-Doesn’t seem linked to the cortex, but rather the power expander. We ran a test of the motors solely on the cortex under a load, and no smoking occurred
-I’m guessing if a wire was plugged in backwards, that would cause smoking (black wire plugged into digital). Would a 2 wire plugged from port 1 and 10 cause smoke if plugged into the power expander’s input? Would it cause smoke if it was plugged into output? Would a 2 wire (instead of a 3 wire) cause smoke if plugged into ports 2-8 if plugged into the power expander’s input? output? Would smoke occur if the cortex 3 wires were plugged into the output rather than input?
-Does this relate at all to PTC burnouts and cortex fuse burnouts, or h-bridge motor controller fires?
The magic smoke is caused by heat. Heat will generally be caused by lots of current flowing through something resistive. In the cortex this often occurs when ports 1 or 10 have their terminals shorted by a motor or bad wire. I’m sure there may be other causes but I’m not inclined to figure this one out by experiments.
well, we had a chip fry on the back of a cortex, it resulted from a short in a wire plugged into a sensor port, this then melted part of the cortexes plastic casing, i’m sure that could cause some smoke
It’s either a problem with the battery, cortex, power expander, or wires. Given that the problem was only present with a power expander, is it possible that one of the batteries was defective or had been plugged in on “fast” charge for too long? If so, that is probably the problem. Otherwise, yes, the issue was likely caused by a broken wire or faulty power expander. Like jpearman said, I don’t really want to try experimenting with the problem. I rather like my room in the not-singed state. 
