Power supply - bang, fizz!

Ever since I was a kid I could detect the strange smell of video arcades.  I would visit my grandparents who lived on the coast of Kent in the UK in a town called Margate that at one time (between 1800 and 1950) was a thriving seaside town that drew tourists and later mods, rockers, and skinheads before its attraction declined to a dreary shell of its former self.  The town was known for its rows of arcades, fun parks and beaches.  In the mid '70s, as my parents drove into the town I could smell the distinct aroma of video arcade machines - the tinny smell of hot metal and electricity.  It was a smell that made the hairs on my neck stand up - perhaps in anticipation of playing Tankzone or Star Wars...

I encountered that smell again yesterday but without the positive excitement.  This time the smell came shortly after a loud bang exploded from a power supply unit.  It's not a noise that I'm keen to repeat but I suspect that there's going to be some investigation required to find a short which is hopefully not associated with a motherboard.  One thing that I'm finding it difficult to identify is the direction that PSU fans should blow - into or out of the PSU case.  In my mind they should be taking heat away from the unit but the unit I'm looking at has two fans that seems to have filled the power supply case with dust and debris possibly causing a short given the sooty black residue that I've noticed.  Anyway, on with the show...

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