Hi,
thanks, its still a little janky!
i read somewhere that the blanking signal for SCART RGB enabling is taken from pin9 of the PAL encoder. so i decided i should fit a more suitable monitor port that has sufficient pins for this and audio too. then i can re-try using the SCART connection instead of the RGBtoHDMI device.
the green signal is the one thats amiss. when the parts arrive for the above, i will desolder the PAL encoder and fit a socket. if there is still no joy then i will get the oscilloscope out!