Hi, vgeorgiev, i have atari clone based on the same controller 6591, i got it two months ago in condition "dead".
I tried as you connect it via coaxial to my tv and didn't find anything, so i just took mixed chroma and luma signals after the transistor, that's worked perfectly, i connected it to my oldschool tv, also i took sound from the coupling capacitor connected to pin 20, that's all worked, but after some time of use it is instantly died and i didn't find out how it happened for now, maybe it is my fault.
For you i can say, that 17.734475 MHz crystal resonator is OK, i have the same, as you can see, 17.734475 divided by four is 4.433618, same value as PAL's carrier frequency, you can check it by Google.
Sorry, if my English is very poor, i'm from matryoshka mother Russia. :3 My advice is to first: check you chroma-luma signal and sound, second: if OK, then you can wire some stuff and f*ck that coaxial, else try to fix it (but this may be a little more tough way).
P.S. i think that my atari might have died by overheating input linear regulator LM7805, because power supply was not original (didn't mesuared real output voltage ), maybe that has created killing power surge.