Chosen Solution
I recently replaced the failing HDD in my iMac with an SSD. All was working fine, i started restoring the drive from my time machine and left the machine to do its thing. I came back to an error about the drive and i turned the machine off thinking i would sort it in the morning (i had created a new fusion drive so i assumed it was something to do with that). the next morning i went to turn the machine on and it chimed but the screen stayed black… tried a few times and no change. I reset the pram etc but nothing worked. I thought maybe i didnt connect the screen up properly but all seemed fine… i also had a spare cable and that also didnt work. since then ive noticed that led1 + 2 come on fine, but led3 is very dim… is this normal or is this a gpu issue? Its about 30% brightness of led1 and 2… any help appreciated!
What about LED 4? Is it on? I would think if LED 4 isn’t lit up then your LCD Panel isn’t being recognized. Is the PRAM reset actually working, you hear it chime multiple times? Do you have an external monitor to plug up and see if you can get external video? I would pull power and try reseating the display cables. It’s worth a try. Meaning of Diagnostic LEDs: 1st LED is the indication of a trickle charge. 2nd is an indication of power being received (machine turned on) 3rd indicates the GPU and computer are communicating 4th indicates the computer and LCD panel are communicating.
