Chosen Solution
Today something very strange happened to me, I bought a SSD for the PCIe connection and leave it for the operating system and leave the HDD for files of the Late 2012 21.5" iMac (13.1) But after testing the SSD already connected when restarting the iMac I get a black screen but the iMac turned on normally because even with a black screen I can see the image I have when I log in I really don’t know if it is the LCD backlight flex cable that is damaged I hope it’s just a temporary thing.
I’m a bit confused, you state you have a back screen but can see image when you log in. Are you using a flashlight shining it into the screen so you can see the faint image of your desktop and its icons? If thats the case then your backlight connection is messed up. Review Step-19 in this guide iMac Intel 21.5" EMC 2544 Display Replacement Did you damage the connector or the cable?
