The Long: I have an nesrgb (toploader) modded by a well respected person who I believe does great work. The mod is for composite, s-video, and rgb. The board is NESRGB14 T.W. 2015 and my output in the back is multiout. Both composite and S-Video work fine.
The cable I am using is the SNES csync multiout SCART recommended by the modder at the time of purchase (I have no idea what resistors are in it). I purchased two (one for my NES and my SNES) and both cables work just fine on the SNES, so at least the cable functions as it should (but maybe not the best choice for nes?). I also tried a sync on luma and it had the same issue.
Other Factors: I know its not an overscan issue, I am using an original power supply. I used to play on a framemeister and didn’t have this issue. However now I play on a PVM and now I see the issue. The framemeister is long gone, so I cannot go back and test it there again. Also, I have not gotten to play much in the last year, so I couldn’t for sure say that the transition is the main problem, although it seems likely and this would lead me to thinking i’ve got some type of resistor issue in my cable. However, I had a bizarre color issue (where the colors would flash to dark and very saturated) with this same mod a few years back, and I sent it back to be fixed. He replaced the color caps, which didn’t help, so then he says he replaced the entire nesrgb board in December 2016. This new board has the same model number as the old board (that color issue was also only present on rgb while s-video and composite worked fine). That makes me nervous it could be other something else and the PMV timing just coincidental, especially because it has been a good 6 months since I touched the nes.
Looking for thoughts and suggestions. Especially if the cable is actually this issue, could it have worked fine with the framemeister and not the pvm? Thanks!