extracting H/V sync from sync-on-green video signal?

[Jules Richardson]

does anyone happen to have a schematic for a simple circuit to extract
sync information from a sync-on-green video signal? 

I've got a screen here I'd like to hook up to the Tek (I left the normal
monitor I use with the Tek at Bletchley), but it needs either seperate H
and V sync lines hooked up, or composite sync - it won't do sync on
green (which is all that the Tek provides).

I keep on finding sync combining circuits that'll do seperate sync to
sync on green everywhere, but nothing to do the reverse!

cheers

Jules