Chosen Solution
A few days ago I tried to install an SSD along with the original HDD, using the tools and instructions from here: OWC Internal SSD DIY Kit for All Apple 27" iMac 2010 ModelsHow to Install a 2.5" SSD behind the optical drive of a 27" iMac Mid 2010 Everything went smoothly but, sadly, when I closed back the computer, it would not power up at all. I opened it again to look for anything that might look off, but I did not found anything obviously wrong. Of course, I also tried disconnecting the new hardware and try to revert to its original configuration, but it would still not power up. The symptoms are: The diagnostic LED #1 does light up whenever the computer is plugged in.No other diagnostic LED lights up at any time.When I push the power button, I can hear a faint “pop” from the speakers, I think.When I push the button to power the computer on, it does not turn on, but I do get 12 Volts between pins 1 and 11 of the logic board (Apple Technician Guide, p. 36, step 7). This voltage remains indefinitely until I hold the power button for a few seconds, as if to forcibly power it down.As long as the computer is in this “on” state, the PSU makes very faint periodic chirp sounds. I do not know if this is normal because it could have always been making them during normal operation and I probably would not have heard them. Anyway, I did make a recording of these sounds: Chirp Noise Any clues as to what may be wrong and how to fix it? Thanks!
I don’t know a ton, but according to the Apple Technicians Guide: LED 1 Indicates that trickle voltage from the power supply has been detected by logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. The LED will remain ON even when the computer has been shut down or put to sleep.The LED will remain OFF only if the AC power source is missing or disconnected, if the logic board is disconnected from the power supply, or if the power supply board is faulty. So your getting power. But there is still a chance the PSU could be bad. Try unplugging everything from the motherboard and PSU that isn’t needed (So pretty much just the hard drives) and then try to boot.
I’m wondering if you might have pinched the SSD’s power cable. The route it takes can put it at risk of a pinch. Loosen the logic board a bit and see if that changes anything. I would carefully pull a bit on the cables to be sure they are loose. Adding a SSD as a second drive shouldn’t have effected anything unless you damaged a connection. Did you have a hard time popping off any off the connectors?
