I know there are several threads about this, but none which I have been able to use to help with my problem. I recently removed my screen from my late 2009 imac desktop and accidentally ripped off my LVDS display port from the main system board. I tried to order a replacement and solder it back on, but it was too small to work on, so I ended up buying a new system board off of ebay. When I had the old system board in, the CPU fan was spinning up to a high level as soon as the machine turned on. After replacing the system board, it is still doing this. Is it possible this is just a problem with the CPU fan itself ? I know many people have talked about putting in a resistor to slow the fan speed, but I find it hard to believe that both system boards have this issue. There seems to only be one connector for the CPU fan, but where does it get the reading to spin up or down? I assume this is from the system board. Is there a way to measure (the voltage?) this from the pins on the CPU fan connector ? Is there a way to test this fan ? Other people have talked about a resistor missing from the system board (near the cpu fan connector - R5797) but I looked at mine on both boards and it appears to be there and looks intact. (see attached). Is there any other way to troubleshoot this or correct the issue ? I have tried all of the software based fan speed control apps out there, and it does not allow me to adjust the CPU fan anymore. (app is showing the RPM @ 0 now for CPU fan). The replacement fan is not a ton of money, I just want to make sure before I buy another component for this system that it is going to work. Any help would be greatly appreciated.