Nikon SB-600

A few weeks ago my trusty Nikon SB-600 flash unit stopped working. I
sent it off to the Nikon service agent (700 miles away) and they
reported that after they cleaned the battery contacts it was working
OK.

I tried to use it again today and everything was working properly -
right up to when I try to take a photograph. All the right things
happen in the window, including the little red light blinking as the
capacitor recharges. But no flash.

The problem is probably the flash but I want to prove that on another
camera. The nearest suitable camera that I know is some 30 miles away,
right through the heart of Auckland. The owner works rather extreme
hours so it might be a week before I get to try it. In the meantime I
would be interested to hear from anyone who knows the workings of
Nikon flashes. What is the most likely problem?
--

Regards,

Eric Stevens