Thank you for your interest and care for all those things about the Dragons.
Yes you are right, I wrote on 27 july "The good input of luma is not exactly the output Y of the VDG ...
For his RGB converter, Retrocant must pick up into the PAL machines and adapt with a transistor or other way a signal similar with the one I named "LUM" present on my RGB PAL Dragons pin 7 of PL6 and pin 7 of PL10 (see first schematic on this topic).
By me, it's somewhere after the output of IC 4053 multiplexor. On my RGB PAL Dragons, the logic circuitry before the multiplexor is quite the same as on PAL schematics of D32 and D64.
For the discussion of all hardware related topics.