Thanks for all the suggestions, but I'm still having problems...
A few questions:
If the image is perfect with the original board, do I need to fiddle around with the ajustement pots on the monitor to get a stable image with advcfg or should the software controls be sufficient?
I have played with a combination of software controls and the pots and the best I could get is sometimes it split in two horizontally, sometimes it split in four uncentered parts.
The board has "vertical centering tabs", could these change anything? Presently, I'm on the righmost of three tabs (looking at the monitor from the back)