Absolutely right. How many times have we 'condemned' an appliance only to find (eventually...) that it was just the fuse?
Re the cooling fan mod to my router, I have now found that a 12v fan on a 9v battery doesn't run for very long so I have rejigged it to run from a 12v mains adaptor.
As I said, it's not pretty but it sure does keep that old router cool!
Cheers,
Roger.