Thanks again rama for all your work on this. I finally got around to moving my previous lash-up into a
project box. Much less of a trip hazard than the mess of cables I had before and good to have everything running off one power supply too!
The insides look like this. I've got the SCART connector wired directly to the scaler input with a 100Ω resistor from composite input to ground. I'm using a Mini VGA2HDMI inside (based on the MS9282 VGA to HDMI chip) as my TV doesn't like 50Hz VGA signals and I'm in a PAL region. All in all I'm very happy with the picture quality. So far I've tested with the following consoles, all working well: Mega Drive, Mega Drive II, Saturn, Dreamcast, PlayStation, PlayStation 2, Xbox, GameCube. My Master System is a bit temperamental, losing sync occasionally on very dark or very bright images, though when I previously had this connected via an LM1881 sync stripper circuit it didn't work at all so I think there might be something amiss with the Master System itself (I'll need to check the capacitors near the video circuit at some point).
The one issue I really have is with my capture box, which can't see the signal at all. It's
one of these generic "HD Video Capture" boxes which normally works fine with the Mini VGA2HDMI's output (when the VGA source is my Dreamcast, Xbox 360, or a PC). I've tried a range of different output resolutions and modes from the scaler and though these all work flawlessly with my TV they will not pass through the capture box.
One technique I've used in the past to resolve issues with HDMI signals is to send the signal through
one of these HDMI/SCART scalers which outputs a consistent 720p/1080p signal that the capture box will always handle (even if the input HDMI signal is changing resolution or in a resolution the capture box handles badly). If I do this here the HDMI output is heavily degraded, with speckly pixels flashing through the image, something I've not see in other configurations.
Do you have any idea why the output from this setup might not work through this capture box? I've tried resetting all settings to default, trying different resolutions, changing frame locking options, anything that looks like it might have an impact on output signal support, all to no avail.
Edit: In case it's of any use, I unplugged the jumper and microcontroller to revert to the stock firmware and can get a picture through my capture box, just with all the problems that the gbs-control firmware fixes. I've tried a number of different screen modes within the gbs-control firmware that I know my capture box handles fine (e.g. 1280x720 and 1920x1080, at both 50Hz and 60Hz) and they all show up fine when directly connected to my TV but when the capture box is in the middle it can't see the signal, either to record or pass on to its HDMI output port.