Atari 2600 A/V Mod problem (NTSC - 4 switch)

Hello Atari owners and modders.

I'm trying to add an audio / composite output on my "new" atari 2600 (NTSC 4 switch), but I can't obtain any image...
The console worked yesterday with RF output, but with no sound and a really weird/dirty b&w image.
That's why I decided to add an A/V mod to permanently solve the problem. I think I choose the cheaper solution: 2 resistances and 1 transistor, similar to the easier-7800-composite-video-mod

My circuit is the same as the solution proposed by brighty83 for a PAL version here (down of the page):http://retro.mmgn.co...ari-2600-AV-Mod
I found the same cicuit on ebay, sellers detail the process on their installation guides for NTSC versions:
http://www.ebay.com/...Upgrade-Kit-DIY (see Installation Guides for atari 2600 4 switch)
or
http://cgi.ebay.fr/A...it-NTSC-PAL-DIY
installation guide: http://www.filedropp...stallationguide (page 10 for NTSC 4 switch)


Here is the circuit (sorry for the poor image quality):


  

Video out and GND ---> Video RCA
Audio out and GND ---> Audio RCA

As mentionned on guides for NTSC 4 switch, I removed the RF box, Q202 and R209:




The sound works well, but no images, it's so sad...

I don't know what to do, and I'm dying about playing with it, in good conditions I mean.
Some of you tried this mod?  any idea ?

Fujisama