NVidia 650 failing repeatedly

September 2013 - the laptop would shut down during graphics-intensive tasks. On reboot, the machine would power on, but with no display. When I connect to the laptop with Teamviewer, I can see in the system report that the discrete graphics card is unavailable. Also, no displays are detected. I tried hooking it up to an external display via HDMI, but it isn't detected. The laptop was under the 1st year applecare, so I had the entire MLB replaced by an authorized service center.

It worked fine for about 4 months. Now, in Feb 2014, the same problem has re-occured. I find it hard to believe that the new MLB can fail so quickly, surely there is some other problem? I suspected some kind of power supply issue, but there aren't any components in between the external power supply and the MLB. Also, did not find any similar complaints or cases reported online. The cost to replace the MLB would be around $700, and I don't want to spend that kind of money if the MLB isn't the real problem.

Does anyone have any ideas? I have read about this problem in earlier MBPs. People have reported that a "reflow" of the GPU is an effective solution. Any thoughts?