Valentin Berlinsky retired from the Borodin Quartet in September 2007 . His place was taken by his pupil , Vladimir Balshin , but Berlinsky still continued to help the quartet . Valentin Berlinsky retired from the Borodin Quartet in September 2007 , and was succeeded by his protÃ gÃ , Vladimir Balshin , but he still remained the group 's mentor .