Do I have a logic board issue?

My black macbook won't sync with ipad2 or iphone4 after latest updates. Both get stuck upon beginning the backup. After a long period I get "unable to sync because ipad was disconnected", same with iphone4. Mac Genius told me it was a software issue at first. Kept my macbook overnight, next day said it a was a logic board problem, $300 to replace. skeptical at this point. Any ideas or suggestions?