Chosen Solution
I followed the guide to replace the failed (according to SMART) SSD and failed (according to completely not working anymore) HHD. System worked fine before the start of surgery using an external drive. Everything seemed to go well, but once back together (except not gluing the screen back on), nothing happens when I hit the power button. The first green LED on the logic board comes on when power is connected, but nothing else happens. I removed and reconnected all the power supply connectors, with no change. Guess I’ll try a complete strip down and rebuild next, unless someone can give some diagnostic tips. Are there places to measure voltage? Any bad connections or reversed connectors that would prevent booting? If I broke the wire in the power button, could I fake a push by shorting across the switch input?
Bryan, Sadly you can’t use the Samsung blade SSD’s in your system (M.2) you need to use a proper 2.5” SATA drive for the HDD SATA port and if you want to use the blade SSD connector on the backside of the logic board you’ll need either a real Apple blade SSD or OWC’s custom SSD for Apple systems. Apple uses a custom connector and the dialog it supports must be AHCI via SATA. Here’s good reference to see the different interfaces
The Red pathway is whats required in both drives
If you have a LED alight, then the board has power. The bootstrap procedure will be looking where? if you have cleared the firmware by removing the ssd then it will be hanging. Try asking on one of the IMac tech forums. I don’t know, but can you boot an iMac from USB or external device? That would be my next step. If you can get ‘something’ to boot up then you can probably re-install the OS. Or maybe none of this is applicable, for I’m not familiar with iMac.
