Famicom AV mod - grainy picture with vertical lines and other problems

[FM-77]

Hey guys! I just AV modded my original 1983 Famicom console following these instructions (note: I used a 2N3704 transistor instead of the 2SC1815 suggested on that site).

When I tried it on my modern widescreen PAL CRT SDTV, the video looked really nice. Sharp picture, perhaps somewhat weak colors, but it looked fine.

When I tested it on my older 4:3 PAL CRT SDTV however, the picture was very grainy and there were vertical "lines" all over the screen, and the colors were very pale. It's playable, but the picture clearly isn't very good.

However, after playing some more, I noticed that when the picture gets too bright (I'm guessing), the picture gets all warped and strange-looking, as it can sometimes look when you get bad reception through an RF connection. This occured on Magnet Man's stage in Mega Man 3 (where it is really bright) and outside the mine in Ys III (where it is really bright).

Example of the vertical lines and the pale colors (click to enlarge)


Example of the "warping", the grainy picture is also very noticable here (the sky is supposed to be solid blue, not blue with white pixels all over)


Any ideas what I could possibly do to fix this? I haven't seen any discussion the the Famicom AV mod around these forums so I couldn't find any helpful topics regarding this.

Edit: The picture is perfect (save for the vertical lines) on the aforementioned widescreen TV, I don't really understand why it doesn't work well on the other TV? All other video game systems work fine on it. Anyway, I'd really appreciate some clues to this. I'd really really do.