We have investigated the whole phase diagram of PbSc1/2Nb1/2O3-PbTiO3 (PSN-PT) solid solution by Raman scattering and compared the results to our recent x-ray and theoretical study on this system [R. Haumont , Phys. Rev. B 71, 104106 (2005)]. Changes in the vibration bands associated to the sequence of phase transitions R3m-Cm-Pm-P4mm by doping PSN with Ti4+ were evidenced, especially between the two monoclinic phases. The detailed analysis also pointed out that the monoclinic order probably already exists into the rhombohedral and the tetragonal phases on a local scale which makes the morphotropic phase region (MPR) more extended than it was reported. Moreover, besides the polar states this Raman analysis evidences the strong chemical inhomogeneities existing on a nanometer scale in such relaxor-based system such as the Ti-rich and Sc/Nb-rich regions.