STEVE JOBS DID IT at . Lou Gerstner and Sam Palmisano did it at . But tech turnarounds are rare. John Chen, CEO of BlackBerry since November, is trying again. BlackBerry is Chen’s second major turnaround attempt. His first was Sybase, a database pioneer that had been crushed by . Chen came in, found a niche in mobile data and sold Sybase to in 2010 for $5.8 billion.