With a lot of help, I've managed to get the RGB2HDMI mod working with my STacy.
I bought the complete kit from "SellMyRetro", which includes the 12 bit buffer board.
https://www.sellmyretro.com/offer/details/rgbtohdmi-for-atari-st~~ste-61574
Here's a picture of my STacy's motherboard, with labels showing where the 3 wires
(Blank, Vsync, and Hsync) go. I'm not sure if this applies to all STacy motherboard
revisions but it works with my board, which is the "C103999-001 Rev.B" version.
The next 3 pictures show me setting it up for use:
Currently, I'm using that popular Dell 27" monitor. Why the Dell? Because the brand new,
never used, out of the box replacement screen and controller board I'd bought to replace
the STacy's original screen was dead on arrival. 😐
I've got another ordered but I'll have to wait for it to get here (slow boat from China, ya
know).
<drums fingers>
I'm posting this to hopefully help any other STacy owners who are planning on installing the
RGB2HDMI mod in their machines.
BTW, here is what you get if you leave your SC1224 plugged into the external color monitor port on the STacy, while running in hi-res mode.