The CFL in the kitchen is left on 24/7 - sometimes they last a very long time, this one not so much.
At first glance it looked as if the windings insulation on the feedback toroid had incinerated, on closer examination; a capacitor next to it had self destructed and sprayed its surroundings with ash.
The capacitor was on the negative end of the capacitive supply splitter in the half-bridge.
All the semiconductors tested OK, but the 2 transistors were heat discoloured.
The 4.7uF/400V electro read about half the rated capacitance and more than the 40 Ohm that the Atlas ESR70+ is calibrated to.
The mains in RFI filter inductor had sacrificed itself to save the fusible resistor.
The CFL was a Philips 18W.