First of all thanks a lot Anemos for the tip!!
I tried the connection in post 1, and it did not work for me (I might have made some mistake when soldering the cables, so it may still work). However, I tried another connection, and it DID work!!! Atarti 1040 STF to Commodore 1084 S-D2 (with Female DB9 in the monitor). Instead of connecting Atari ST Pin 2 to DB9 Pin 7 (V+H sync composite), I connected Atari ST pin 9 to DB9 Pin 8 (H-Sync) , and Atari ST Pin 12 to DB9 Pin 9 (V-Sync).. And it worked!
In practice, instead of building a new cable (after my failed try), I used an Best Electronics Cable (http://www.best-electronics-ca.com/monadapt.htm
) and built a DB15 to DB9 adaptor adaptor with these terminal breakout connectors:
I ConnectedDB15 ----> DB9
Red (Pin 1) ----> Pin 3
Green (Pin 2) ----> Pin 4
Blue (Pin 3) ----> Pin 5
H Sync (Pin 13) ----> Pin 8
V Sync (Pin 14) ----> Pin 9
Ground ----> Pins 1,2, Ground
I did not use the resistors mentioned by Anemos, although maybe there are some in the Best Electronics cable..
Thanks again and good luck if anyone is trying this!