Had the same issue, but I got better results by removing the resistors on the combined sync output. I ditched the 1k-to-ground resistor as well as the 470 ohm resistor and it worked great when run directly into the GBS' VGA input. The circuit has pretty significant voltage drop vs. the original voltage of either sync line; I realized those two resistors on the C-sync line attenuate it even more, which is totally understandable for the original application but it's overkill for the GBS board, *especially* if you're already using a 100 ohm terminating resistor on the GBS. (I don't even use the 100 ohm terminating resistor, tho, since I don't need it.)NoAffinity wrote:I tried integrating the simple sync combiner circuit talked about on retrorgb, into the vga input, and didnt have any success. Jumbled image, never did get a good synced image, from either rgbs or rgbhv sources.
It's amazing if you wanna use something like the Retrotink 2X in passthrough mode! Slap a passive HDMI-to-VGA in there, throw on the sync combiner and you're upscaling S-Video and composite signals easily.
Would not recommend it on signals that are already RGBs though. The resistors + general behavor of the transistor will scramble a C-sync signal. I could see wiring up a DPDT switch in a slightly convoluted way so that one position will run the H-sync pin through the circuit and the other position would run it through a resistor straight into the GBS, though, if you want the adapter to be the last link in the chain before the GBS. That's what I'm gonna be doing eventually, because my current RGB/RGBHV switcher requires a minimum sync voltage of 1.7v and the combiner circuit drops it below that once it's connected, due to the switcher's own terminating resistance.