N_Cook wrote:

http://home.graffiti.net/diverse:graffiti.net/sf2.jpg
No markings, a black potted box 7x7x 15mm external dimensions.
If a stepup transformer , why so small?

As per the other poster, it's likely the trigger transformer.
They're usually quite small, as they have few primary turns, lots of
secondary, and since the wire is quite thin (impedance isn't a problem as they
don't supply any appreciable current), they end up quite small.
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