I’ve got the dead buggers sat in a box for later depotting and examination, as I’m also confused as to how a relatively small shift in frequency would kill them - can’t be voltage as I monitor that and it’s more stable than the public grid, and it was only after I started using frequency shifting that they all started flickering and ultimately died. I’d have assumed they’d just be using a boring bridge rectifier or something, and that they’d be expected to work at 60hz too - so yeah, agreed it’s bizarre. I can only think resonance might be at play, as in the evenings it sits at a pretty consistent 52.8 hz.