[Coco] RGB cable for Samsung SyncMaster 711mp

[Ken H.]

I have built a Coco3 RGB to SCART cable for my Samsung SyncMaster 711mp
monitor but the image is jumping around.  You can see it in this short
video here: http://youtu.be/5Jm2T_HyK5E
What's wrong? Is the Sync signal wrong or perhaps this monitor doesn't
support 15khz RGB? (although I believe it should)
I have used a 74ls02 to create the composite sync.  Scart Pin 8 has 12 volt
and pin 16 measures about 5v.
Can you tell what's the problem based on how this image looks?
thanks
Ken