Default [Q] HTC desire SV random crashes and reboot!!!

Hey guys..I bought an HTC desire SV in Dec 2012 nd after 4-5 months it started giving random reboot issues..first time they ( the service center geeks :P) reinstalled the OS..it stopped for few days and then started crashing again. In the 2nd servicing they changed the main board. It stopped for 1 or 2 months ( little longer this time) and then started again. Phone storage, internal storage and memory utilization is under normal conditions. I have only 3-4 external apps installed. Any help is much appreciated.