Slightly dim S-vid output on low serial AES...

I have an AES here with a story. I think it's S-vid output is a tad dim, and I'm looking for ideas. I think it's story is relevant, so read on...

I bought this AES broken. Serial 0121**. When I got it, it had a botched BIOS socket install. I sucked out all of the mess, and rebuilt the many broken traces. At pwer up however, I realized - no power. A quick scan of the entire board yielded that the large green transistor was missing (the one near the power switch). I replaced it with one from parts, and voila, power. However, the video signal was a bizarre yellow static (not the standard BIOS error garble).

Another close inspection yeilded a missing ceramic cap. I replaced it, and had solid yellow. Great.

At this point I'm beginning to think I may be wasting my time. For the hell of it, I pull off it's video daughtercard (the card above the mem slot) and swap it with one from a hatched parts board (serial 0231**). BINGO!!! Away she boots, with the tune we know and love.

So I finish the mod job. I tap composite from the jack, tap the stereo, and do the standard 75/33 S-Video mod written up by the master JMKurtz.

It seems to me, the S-video signal is marginally dimmer (the pure white in the Neo boot up screen seems a very bright grey) than the S-vid the same mod gets me on my personal AES, and it's definitely not as bright as the composite signal, though far clearer and nicer.

I doublechecked the circuit. I tried altering the 33ohm luma values, with no change to brightness. I doublechecked that the circuit was getting a good 5v, and it is.

I'm wondering if this is related to my daughtercard swap.

This problem is not really serious. If I didn't have my personal AES to compare, I wouldn't even notice the slight difference. I'm more curious as to what may be causing this variance, and what aspects of the circuit (on the AES board, or the S-Vid circuit) I may be able to tweak, to tweak the output.

I want to learn more about how this circuit works. Any ideas?

Maybe the trimmer capacitors? The yellow things on the main board and on the daughterboard?

I saw what looked like a trimmable pot/cap on the daughtercard. I tweaked, with no change to composite or S-vid, which seemed odd to me....

I didn't try the one on the AES board...

You could remove the daughterboard and see if you get any difference in the video signals.

Won't I lose composite altogether by pulling the daughtercard?

You need to put the main crystal (24MHz) back in its place on the board.

That's the spot with the silhouette, that the daughtercard has leads going to, correct?

What is that daughtercard really doing? It seems too complex to be a simple amp.

I think there was some interference problem caused by the old crystal/clock, the same 24MHz crystal that you find on MVS boards. The very first AES boards are the only ones to have it. The first fix was the daughterboard that has the main crystal relocated on it with a slightly different frequency (24.167829MHz). The daughterboard should be meant to modulate the clock frequency. Later revisions also have this fix but built-in.