Chosen Solution
I was replacing my optical drive in my Mid 2011 27” iMac. I’ve done some repairs on similar models before. Whilst putting the LCD back on I accidentally damaged the CPU Fan Ambient Temperature Sensor Cable 593-1361. I thought it wouldn’t effect the iMac as it was only a trigger for the fans, and that I would replace it later. When I turned the iMac on the fans became very aggressive and the iMac booted halfway and then the LCD turned off but the fans continued aggressively, I tried putting the iMac into safe mode, but it didn’t work. I then tried putting it into Internet recovery mode, and it completed the spinning earth cycle but froze on the Apple Logo. I understand the wire is most likely the problem for the aggressive fans, but surely not for the half-booting LCD? Is it because of the CPU Fan Ambient Temperature Sensor Cable 593-1361 or is there another issue?
Yes! The sensor is needed! SMC requires the input, if it doesn’t see it SMC will push the system into Safe Mode, pushing the fan to the limit and lower the CPU’s clocking to a crawl!
