Know of any CPU switch on the logic board?
I purchased a used, but tested logic board for my A1212 Mid 2007 Macbook Pro 17". The video adapter on mine had failed. This used version was "tested" working with a return policy and the seller, Komputech had very positive ratings on eBay.
I followed the guide here on replacing the board and all seemed to go well. I closed the machine back up and when I went to power on, I could hear the fans spinning, The power light on the front of the case came on, but that was it. No beeps, no Mac chime, no display, no nothing.
Worried that I missed a cable connection or damaged something during the process, I started over, removing the board, cleaning the thermal paste and reapplying and reinstalling. Same thing.
So then I did it all again with my original board. The one with the video problem. It booted up just fine, just with the corrupt/pixelated video issue. This told me that I had done the install properly and hadn't broken anything else in the process.
So, I wrote the seller on eBay telling them it looked like the board was defective. In his response to me he asked if I "could look into my CPU, please make sure you are turning the knob to engage it." Whaaa? I almost thought it was a joke. Then I wondered if there was some switch or toggle that I needed to flip. Didn't see anything in the guide about this, or anywhere else I searched online.