Foolproof power supply interfaces

[Peter Coghlan]

>
> I've done worse--used an AC-supply wall wart on a piece of equipment.
> Poor thing didn't stand a chance.
> 
> You'd have thought that after all these years, some sort of keying
> system would have been developed, but I guess not.
>

I'm not sure it would help.  What do we get when we try to make things
foolproof?

A friend asked me to fix his mains powered radio which he said used to work
but had stopped working.  I thought the mains lead looked rather flimsey but
I said I would take a look at it anyway.  I opened it up and found that the
power went directly onto the PCB where there were some damaged tracks.  There
was no sign of a transformer or other evidence of a power supply section.

I asked my friend if anybody else had done anything to the radio before
he asked me to look at it.  He said there used to be a big black heavy lump
of a moulded plug on the end of the mains lead but he got someone to cut it
off and change it for a normal sized plug because it wouldn't fit into the
socket he wanted to use it with which was too close to his worktop.  He
didn't recall hearing a bang when he first plugged in the new arrangement.

Regards,
Peter Coghlan.