Archibald Tarquin Blenkinsopp Esq wrote:


Thank you, it suggests that there may be an inherent problem as mine
blew on switch on too, both of them.

Clever these Chinese :-)

Could the problem be tin whiskers ?

Maybe a second attempt to use them will find them functional.

Or, maybe a fault other than across mains will reveal itself.

Before the ROHS era, we had an experimental assembly at work
which did this. Some genius changed the previous generation
gold-on-ceramic design to a pure-tin-on-ceramic design. You
could plug them into equipment, and roughly 365 days later,
a short would develop. Once we knew what to look for (it was a low
voltage assembly), we could take a microscope and a hobby knife
and cut the whiskers and reinstall the module. They would of
course, grow back. Cutting them, is a workaround.

What I don't know right off hand, is if tin growth needs bias.
And whether tin would grow if the assembly was just stored
in the box for a year.

The idea is, the Chinese production could do functional test,
the unit could pass, they put it in the box, a tin whisker
grows and shorts mains, you plug it in and it blows.

Try using the module again (if you dare) :-/

Paul