Upon connecting it up I noticed the fan wasn't operating resulting in the card overheating and shutting down. I checked the fan operation independently by connecting it directly to a power supply and function generator - it was working correctly with variable speed according to the square wave frequency.
I then checked the output with a multimeter/DSO and verified that the GPU was putting out both 12V at pin 2 and PWM at pin 4. However, when the fan is...