Hi Mr FJC,
Apologies I have been away with work so no time to tinker with the Atari, just been on it.
Glad you mentioned the PAL/NTSC master clock jumper's being reversed as I only get an image when its on NTSC which mean's it PAL which is what my Atari is.
Okay, things I have tried since I last posted,
(1) Tried a different CD4050 chip from an 800XL, made no difference.
(2) Desoldered the CD4050 and replaced it with a CD47HC4050 chip (Found after googling and reading about an Atari VCS mod) apparently its a faster version of the CD4050, which gives me a more stable image when taking csync off of pin15, however the board is still providing artifacts on the screen. Fine on blue boot screen when I load VBXE game Nightshade there are artifacts on the bottom left of the screen. If I run the output back through gate Pin 9 and take the output from pin 10 it is still a little cleaner but still not great.
(3) Do mod number 2 above, then putting a 100nf cap across the connection to gnd doesn't really improve the situation, the picture deteriorates if anything. Still using Nightshade game as a benchmark for image quality - not sure if this is sensible or not.
(4) With the CD47HC4050 installed and i take comp video from the monitor port, then use a 100nf cap to clean the image, Yes the grainyness goes but then you load nightshade and the black parts of the screen look like a "Car Crash", 200% more artifacts.
I will tinker a bit further over the weekend.