Re-visiting the revised video output section.
In order to better ascertain if my simple transistor buffer design would work, I built a little test board to take the place of the UAV on one of my 1088XEL's.
I just noticed I stuffed a 1K resistor for R1 instead of the spec'ed 1.5K resistor.
Hmm... after checking on a scope, the output looks good, so I think I'll keep it that way.
After firing it up I noticed that there were evenly spaced vertical lines in the S-Video display. Argg the dreaded vertical banding problem has reared it's ugly head !!!
Example of what those vertical lines looked like (image courtesy of this POST) ...
This is caused by chrominance bleeding over into the luminance line. I had thought by adding an independent transistor buffer stage for the composite video output prior to injecting the chrominance signal, that I would avoid this problem. Well I guess the answer to the million dollar question is "No it didn't".
So for now I eliminated the entire composite output circuit, but the real culprit is capacitor C2. Just clipping this out of the circuit solved the issue.
And now for the comparison test results (These are not video captures. Taken with a camera looking directly at an LCD monitor)...
The S-Video results are very good indeed. And for all practical purposes looks identical to the UAV's video output in this regard. This I am happy about .
In order to solve the chrominance bleed-over caused by adding the composite video output circuit, would likely take a true video buffer amplifier IC to isolate that part of the circuit from the S-Video outputs. Unfortunately those video buffer ICs have gotten pretty scarce and expensive in a single supply thru-hole device. So I'll need to put on my thinking cap to see what alternative approaches could be used to satisfy the requirements. for the time being I like the S-Video results, and will be keeping that part of the circuit in my 1088XLD design.