OK, finally, HP came and fixed the printer.
Previous tech was a moron and reassembled the machine like a retard.
So now :
- after cleaning heads, calibration scan axis, etc., I have not the horizontal lines I had previously,
- but, there is another catch, instead of horizontal lines, I have now vertical bandings, very regular, 2 mm wide
HP techs suspects printing unit ("printing cart", in french "chariot d'impression"). He will be back and install a
Any advice ?