Powergraph Light also works this way (via OSSC VGA-connector input but in 15 kHz of course), and the signal is not too noisy in my experience. If you connect MSX video output to SCART and V9990 to VGA input with an audio splitter cable you can use OSSC remote to toggle the visible "monitor" which is handy. You may also need a SCART breakout to steal the audio from there instead of splitter depending on whether the MSX has separate audio output connectors and whether the SCART gets is audio there or from a consolidated av connector on the MSX. In some models you don't need either splitter or breakout
well, first try to connect rgb to vga directly failed, ossc got no signal in the vga input. I guess my solder skills are worst than I could imagine, I may have missed a proper connection in all those gnd pins...will try again.
the cable I ordered (rgb->scart, still waiting the ~15 days of manufacturing) is from RetroCables too.
Did you try RGBS rather than RGBHV setting on the OSSC already?
Also I believe for sync you will need separation with level translation/analogue-to-TTL translation
As mentioned earlier in this thread and in the official documentation, RGBHV and RGBS modes require clean TTL-level sync signals and cannot extract sync from composite video or luma
