Having problems with NESRGB mod (sync?)

[bmwsvsu]

I'm about ready to give up trying to figure out how to fix this problem, so I'm hoping one of the experts in here can help.

First, here is a video demonstrating the problem (you must play it at 1080p, 60fps to see the problem):

https://youtu.be/pg9UHf7KhyM

This is my modded NES (etim) connected via an XRGB-3. Towards the very top of the screen, there is a horizontal wobble that goes back and forth between 2 different positions very rapidly. When my XRGB-3 is connected directly to a CRT monitor, this back-and-forth oscillation happens so rapidly that it looks basically like 2 separate images superimposed over each other on the screen. When routed through my capture card, the effect looks different, with only a few wobbles per second (as seen in the video when played at 1080p, 60fps).

I think the back-and-forth oscillation though is happening at exactly 60hz because if you play the video back at half that rate (30fps such as at youtube's 480p setting), the wobble disappears completely (suggesting that it goes back-and-forth once in the time of 1 frame at 30fps so you never see the alternating wobble) and all you see are the curvy lines when I'm adjusting the AFC settings. I can correct this to some degree with the AFC settings, but even when at the max stable picture (setting of 6), there is still wobble in the top of the image. On a direct CRT monitor connection, there is no instability below the top 4 or 5 rows of pixels so its no big deal because I can simply move my image up until the wobbly part is no longer visible, but on my capture device, it still makes much more of the image unstable - probably the top 20 percent or so. So I can't capture video like this.

I've tested two different modded NES consoles, and also have done so with an XRGB-2 and XRGB-2 plus. Same problem across the board with all tests.

Any ideas? I'm guessing it is sync-related since I can reduce the effect somewhat with AFC.

Also worth noting is that the same problem is present in the S-video output as well.

[viletim]

The NES/Famicom removes one pixel from the first line of every second frame. The reason is that it changes the look of the dot crawl to make it look less ugly on CRT television sets of the time. It causes the symptoms you describe on scalers that aren't expecting the tricky timing. It's not really NESRGB related specifically because an ordinary NES does it too.

[bmwsvsu]

Thanks for the info.

Are there any known scalers out there that do a better job of handling this signal? So far the XRGB-3, XRGB-2, and XRGB-2+ all suffer basically the same with the XRGB-2 maybe handling it marginally better due to the more precise AFC control settings available.

EDIT - is there any way to pre-process the output from the NES before feeding it into the XRGB scaler such that the very first line of output is not fed into the scaler? Like a device that can slightly over-scan the signal to be output to the scaler? I know some Extron devices have vertical position control, I didn't know if inserting something like this between the NES and the scaler might correct the problem.