I have been wanting to do this for awhile but have not gotten around to it. I took my Open Bench Logic Sniffer and sniffed the e (in picture from top to bottom) of the Atari 7800 MARIA chip. This is what the signal looks like before it goes into the video mod (D/A converter).
I am still learning how this translates into a picture on the screen. If anyone has any insight into this let me know.