Chosen Solution
I recently tried upgrading my Late 2015 17” iMac to an Intel i7-6700K CPU and an NVMe SSD. However, when I try to turn on the computer, three weird things happen. First, I do kind of hear the startup chime, but it is very distorted. Second, the main display remains black and does not turn on. Third, the fan ramps up and starts spinning at full speed. The following video shows all of these problems https://drive.google.com/file/d/1M3suMFf… I took off the screen and on the main logic board, the troubleshooting LEDs #1 and #2 turn on normally. LED #3 also turns on, but is a little fainter than the other two. LED #4 does not turn on, but this is normal since I removed the screen. I reconnected and disconnected the speakers, but this had no effect at all. Strangely enough, removing some of the ram did reduce the distortion of the sound. The next thing I am going to try is to take the whole thing apart and reseat all the connectors. I think that the CPU should be fine since LED #2 turns on and I hear the startup chime. I tried searching for this issue, but it seems that nobody has experienced these exact symptoms yet. Any help or insights would be greatly appreciated!
Update: It turns out that the CPU I was using was defective. I returned that one and bought another i7-6700K. Everything is working perfectly now, including the SSD upgrade.
You’ll need to take the SSD and adapter out of your iMac and place it in a MacBook Pro the setup or just replace it with a better drive for your system OWC Aura Pro X2 SSD I don’t recommend this setup in iMac’s given the amount of work that’s needed to get to it and these adapted drive setups don’t work that reliably (as you encountered)
