Chosen Solution
Hi to everyone! This is my first time here posting a question, although i have always been a regular user of iFixit, helping me with a lot of issues. However, I’m having a strange problem and cannot find a specific answer for it. As a start, sorry for my english not being it my first language. I have disassembled today my iMac to add an Apple SSD Drive 128Gb so I would enable Fusion Drive (having a 1TB HDD 7200rpm). Everything went smooth, but when I put everything together, there was no image on the screen. Having disassembled notebooks, computers for about 12 years, tried the usual troubleshooting and came to the conclusion, with a torch in my hand, that the LCD was working, the iMac booted fine, but there was no backlight. So i took out again the LCD, tested the cables on the back of the LCD thinking i had torn any of them. Tested the display cable, the power cable of the lcd, everything ok. I then thought it was maybe a problem with the light sensor, or maybe the light was dimmed at it’s lowest value, nothing. Reopened the iMac, removed the SSD drive, still the same. Has this thing happened to anyone of you? I can’t seem to find nothing about the new iMacs, only about the older ones. Hoping for an answer.
Finally i got my iMac working. The problem was that 1 pin of the LVDS cable (Or the DisplayPort Cable) was disconnected from the cable. So for anyone that might have a problem like this, with no backlight, on the iMacs 2012 or newer that have the backlight controller integrated on the motherboard, make sure that the Cable that connects the display data to the motherboard, is not damaged. I had to put it under microscope, because there was no way to find it out just looking at it, considering how small those pins are. Although the LEDs have a power connector, if the DisplayPort cable (LVDS) cable does not send the command to power on the LEDs, it will not power them. Take a look at the picture.
While I can’t offer you much of an answer here: The reason you can’t find much on the newer systems is they are harder to open than the older units, which is why many people have not ventured inside. As to your problem: Check your displays power ribbon cable connecting to the logic board and its connector did you damage it? Also if you did not seat it fully before powering it up you could have blown something.
