many moons ago i started a project and ran a mac analog board at VGA resolution. problem was, the tuned circuits in the horizontal deflection stage needed re-tuned and redone. there was so many foldover and linearity issues in the horizontal, it wasn't even funny. I used a local PLL locked horiz oscillator. then i used a national semiconductor video amplifier IC using the back porch flyback pulse from the local oscillator and a tap off of the flyback. its been long ago, i cant remember exactly how i did it.
but the V sync could directly drive the Vertical stage no problems. it was the horizontal and video amplifier stages i had the most fun with.
But i could see a very decent picture on the screen of 640x480, 32bit grayscale. problem was, the horizontal linearity was messed up, and the picture was "rippled" in the horizontal stage. the yoke and everything just wasn't tuned or impedance matched at the higher 31khz.
But it did work. I tried replacing some caps and changing the linearity coil from one of an old VGA monitor, and it did improve the picture alot, fixed the linearity, and removed some "waves" in the picture. but the picture just wasn't that great as it still had some ripples in it from the "mis-tuning" of the yoke. But i guess if i would have put a pi-filter network on it, it would have fixed it, but it wasn't worth too much more effort. Also the flyback got hot, dangerously too hot, probably from core saturation. so i never finished the project.
but the V sync could directly drive the Vertical stage no problems. it was the horizontal and video amplifier stages i had the most fun with.
But i could see a very decent picture on the screen of 640x480, 32bit grayscale. problem was, the horizontal linearity was messed up, and the picture was "rippled" in the horizontal stage. the yoke and everything just wasn't tuned or impedance matched at the higher 31khz.
But it did work. I tried replacing some caps and changing the linearity coil from one of an old VGA monitor, and it did improve the picture alot, fixed the linearity, and removed some "waves" in the picture. but the picture just wasn't that great as it still had some ripples in it from the "mis-tuning" of the yoke. But i guess if i would have put a pi-filter network on it, it would have fixed it, but it wasn't worth too much more effort. Also the flyback got hot, dangerously too hot, probably from core saturation. so i never finished the project.