Thanks again here Peter and Graham ..
So about 200 lines are the limit in mode line ? is that with 50 or 25hz framing ?
I wonder why i would think it would be the other way around trying higher line rates .
Its a pity we could not test different brands to see unless some one else on the forum has a different one to test this .
Graham as you know most tvs use the horizontal for the eht generation ,i went a different way with my monitor i am constructing ,has its own inverter which is independent of the horizontal so just a matter of what the yoke can cope with frequency wise which is wider than i would of expected but do have to put up with adjusting screen size raster position .
Peter so if 200 lines is the lowest limit we would need some thing like my circuit Steve Anderson came up with for me on my monitor feeding this to a 4040 ic out put would divide by 2 4 8 16 so on to get the lower line rate's down to the NBTV standards 256 lines or higher would be some thing to try this way to get down to 64 and 32 lines .
Chart showing line frequency left with frame rate top resulting line numbers
Can the framing be dropped to 12.5 hz ?
again a divide by 2 circuit can fix this and mix the sync to a composite video or just feed to a scope circuit as think you did for the 240 line experiment.
so one way or another electronics will find a way
I looked into the video card some sellers a pretty cheap i should be able to order one in a week or 2 .