Call AppleCare at 1-800-MY-APPLE, and state your case. A logic board reset is quite common, and is sometimes a good fix for freezes, boot problems, and a few other types of strange hardware-like symptoms. It's also a way to claim a small warranty reimbursement if no real problem is found, and the unit passes other hardware tests. If the service center also charged you a troubleshooting fee, then you might be OK in trying to reclaim that.
Sorry to say, some hardware problems are not going to be found easily at a service center, as they can be heat-related, or can only be seen when other hardware that you have at your site are connected, and the service center may not be able to test with everything that you may have connected.
As Diablo stated, if your system is now failing a video test, then the only likely fix is to replace the logic board. Apple might offer a repair exception if a reasonably short time has elapsed since the first checkout, say less than 30-45 days.