The speed controller of a lathe I have has exploded. I have located a replacement, but while that is shipping, and before I install it, I want to understand why the speed controller exploded. Here is a partial schematic, the most relevant bits, deduced from the circuit board. Visual inspection shows a rectifier diode used its anode leg as a fuse, and one small surface-mount capacitor disintegrated itself.
What I do not understand is why the controller failed in this way. (I am not an EE engineer, but I can understand the basic idea behind this controller.) I can understand the rectifier failing if the motor shorted out. (Its rated 8A while the gated diodes in the bridge are rated 15A) However, so far the motor checks out, no obvious shorting, but its still being tested. And I do not understand why C6 failed, or how it could have caused the rectifier to fail.
Any enlightenment or suggestions would be appreciated.