A little bit more progress. I added a voltage reference (TL431) in the video comparator circuit to get a more stable threshold and tightened up the wiring. That seems to have eliminated the vertical bars on the left side of the image.
For the video signal, I also took U1 (the 7438 NAND/inverter) out of the circuit and hooked up the video comparator output straight to its output. My guess was that the 7438 might be too slow for higher-res video. Removing it seems to have helped a bit with the dark image problem at higher resolutions.
Here's a VGA input now. The overall geometry is cleaner, but it actually makes some of the smaller imperfections more obvious:
A couple notable issues. First, each video line starts in a slightly different place, which you can see when looking closely at the edge of the picture. Also, some lines are brighter than others which shows up as horizontal stripes in the image. One or both of these is probably now from the lack of phase lock between the flyback circuit and the yoke driver circuit. Some kind of PLL is probably the next step.
Here's 832x624 now. Still needs more width, and it has some rollover, but at least the video is visible:
techknight, that's a helpful piece of info on the split horizontal systems, specifically the fact that they all have an extra transformer or inductor. I wouldn't be surprised if it was just a straightforward inductor which serves the same function as the flyback primary in a combined system. I plan to do some experiments with adding an inductor for this purpose, which will let me add the DC-blocking capacitor (C15) back into the circuit. If that works it will get rid of the horizontal offset problem and save some wasted power.
For increasing the voltage, that just takes a different power supply. The benchtop supply I have right now tops out at 20V, but the circuit could easily be run at a higher voltage and will undoubtedly need to be for the higher resolutions.
I also just bought a Radius Pivot SE/30 PDS card (plus a IIsi Radius card and angle riser card) so once the higher res is working I should be able to drive it from the SE/30 itself rather than the external video source I'm using now.
For the video signal, I also took U1 (the 7438 NAND/inverter) out of the circuit and hooked up the video comparator output straight to its output. My guess was that the 7438 might be too slow for higher-res video. Removing it seems to have helped a bit with the dark image problem at higher resolutions.
Here's a VGA input now. The overall geometry is cleaner, but it actually makes some of the smaller imperfections more obvious:
A couple notable issues. First, each video line starts in a slightly different place, which you can see when looking closely at the edge of the picture. Also, some lines are brighter than others which shows up as horizontal stripes in the image. One or both of these is probably now from the lack of phase lock between the flyback circuit and the yoke driver circuit. Some kind of PLL is probably the next step.
Here's 832x624 now. Still needs more width, and it has some rollover, but at least the video is visible:
techknight, that's a helpful piece of info on the split horizontal systems, specifically the fact that they all have an extra transformer or inductor. I wouldn't be surprised if it was just a straightforward inductor which serves the same function as the flyback primary in a combined system. I plan to do some experiments with adding an inductor for this purpose, which will let me add the DC-blocking capacitor (C15) back into the circuit. If that works it will get rid of the horizontal offset problem and save some wasted power.
For increasing the voltage, that just takes a different power supply. The benchtop supply I have right now tops out at 20V, but the circuit could easily be run at a higher voltage and will undoubtedly need to be for the higher resolutions.
I also just bought a Radius Pivot SE/30 PDS card (plus a IIsi Radius card and angle riser card) so once the higher res is working I should be able to drive it from the SE/30 itself rather than the external video source I'm using now.