Starting from this thread
http://www.vintage-radio.net/forum/s...hlight=foth+tv
I thought I'd see if I could get 240 line operation working with a similar graphics card. I initially tried using an nvidia 290 with my Win 7 64 bit PC but no joy. An email to Jeroni Paul the author of the Modeline Editor let me know that the nvidia is not compatible with Win 7 but he explained that the ATI cards are. I then bought an ATI HD2400XT and tried loading the modeline from Kat Manton and Jim Beacon
http://www.vintage-radio.net/forum/s...light=240+line
This resulted in a 50Hz 520 line output. I struggled with this for a bit and contacted Jeroni Paul again. He was very helpful and suggested that the very low pixel clock rate could be the problem and he also offered two alternative modeline suggestions:
"If the problem is low pixel clock it is easy to increase, try these:
Modeline "1120x220_25 6,0kHz 25,0Hz" 7.488 1120 1136 1168 1248 220 221 233 240 -hsync -vsync
Modeline "1680x220_25 6,0kHz 25,0Hz" 11.232 1680 1704 1752 1872 220 221 233 240 -hsync -vsync"
The first didn't work and the second gave an image with only about a quarter of the line width filled but it dawned on me that in trying to display 405 lines with RAMBO1152's scheme I had to adjust the aspect ratio of the source material, increasing its width by 20%
In the 240 line case the aspect ratio change needs to be more dramatic and you can see the source and the 240 line 25 Hz image on my HMV901 below. (Yes, it does have an annoying flicker.)
The picture is far from perfect but the old set is doing quite well given that the H and V syncs are just combined by crude voltage addition and it doesn't have the V8 triode fitted in the line timebase.
Very many thanks to all those who whose work has helped me get a result.
Oops! I should also add thanks to Darius whose modulator circuit I used.
Peter