jay123035 wrote:I am wondering what let the smoke out.
the Zener diode?
First off, do any of those look like they suffered?
How could a cap go faulty? Either short or open circuit.
If either cap went short, the output would go to zero, so it wasn't that.
If Cin went open, it's possible for the chip to oscillate, going from 0 to 13v and back rapidly. Probably not sit at 13v permenantly.
If Cout went open, the result would depend on what's being fed - the Pi's C6 may be enough to smooth the o/p, or maybe not.
If not, the feedback would immediately tell the chip the o/p was too high, and switch off, so (probably) you'd get spikes of 13v separated by 0v, which would be smoothed out by the Pi's caps to less than 5v
How could the choke go faulty? Again, either short or open circuit.
If it went open circuit, you'd get no output at all.
If it went short, the result would be somewhat similar to Cout going open, but the chip wouldn't like the large current into Cout, and would either shut down or fail.
It isn't a zener, for a start, it's a schottky diode - different thing.
If it went short, you'd get 0v (and a blown chip)
If it went open, there'd be no path for current during the part of the cycle where the chip output was off. That would mean a large negative voltage being driven back into the chip.
It would also mean (probably) low output.
So we're left with the chip.
Or a bad connection on your circuit - such as the feedback pin being open circuit.