Frightening stuff.
I was fiddling with the speaker cables (stupid banana plugs, ahem) when suddenly, pop, smoke...
One fresh BC516 darlington gone in smoke, fried, belly-up, kaput. Overload beacon lit.
?????????
Yes, the protection circuit, the one I repaired, bla bla bla.
Thing is, I had forgotten to test the b(beep)y relay diode. It was shorted! At least it proved that the detection circuit worked—it did, since the BC516 fried!—well sort of then!
Anyway, fixed! Phew!
Another lesson learnt, I should have known better, shouldn't I?