Two of us on a recent trip to Brazil experienced failure of our 550EX. It was hot and very humid. My flash made a loud popping sound, very similar to a burned out light bulb (large), and the lcd display flashed twice before the whole unit went dead.
Any similar experiences?
Any idea what went wrong?
Cost to repair?
Suggestions for replacement?
Is the 580 more robust for travel?

Thanks,
Marv

580II's your best bet.