Hi all,
finally, I took time friday evening to put the printer on a table in front of me, opened a beer, rolled a cigarette, and did some adjustments on the printer. Especially the pulley of the plate, Y Axis. And now it's working very fine with Cura, I had a great surprise with a really good accuracy.
I also checked some screws like those fixing the vertical supports. I moved the filament spool holder at the left most extremity (I noticed that the spool is making some small vibrations when it rolls when the filament is extruded). Maybe I will build a better spool axis to ensure smooth rolls.
For me, now, I can say that problem is solved. Thanks a lot for help and posts.
Tom.