iMac 27" Retina 5K i5 3.2Ghz no chime, no display, LED 1 and 2 on

[moritz1992]

Good evening guys, im new to this forum and searched around it to find a way to fix my broken imac 27 retina late 2015. Logic Board is 820-00292-A
Here´s the problem :
After i changed the blade ssd with an NVME SSD and accidentially bent some cpu socket pins (managed to get them straight up again, one pin broke but seems to be N/C) while trying to get some fresh thermal paste, i hear no chime and have no display. LEDs 1 and 2 are green but 3 and 4 not. I did some measuring and it seems that gfx_ok, is ok but dp_ok, is not okay. Checked some caps and diodes in circuit but everything seems fine. I changed internals to orginal but same issue. Looks like the Graphics Card crashed or maybe a problem with the smc?! smc switches the DP_ok line . SMC reset doesnt work because i only have bluetooth keyboard and my usb keyboard seems to have no connection. I am no professional but have basics in smd soldering and even managed to repair all kind of electronics in the past. Also excuse my bad english, iam from germany and know only the english i was thaugt in school.
Maybe some of you guys can help me out with some advise. Thank you very much

[reformatt]

Re: iMac 27" Retina 5K i5 3.2Ghz no chime, no display, LED 1 and 2 on

If you have CPU Vcore present, but its not POST'ing (no chime), then it's highly likely your problem is your CPU socket. CPU never needs to come out unless you are upgrading it. Why remove it to change thermal paste?

[moritz1992]

Re: iMac 27" Retina 5K i5 3.2Ghz no chime, no display, LED 1 and 2 on

Hey,
thank you for your reply. You´re absolutely right! I studyed the schematics and boardview i got from another post and found out that the broken pin was for RAM Slots "A" . (exactly it was the 6th one from the right side of the socket if you look at it with Ram slots facing downwards)
I then removed the Ram sticks and tryed the "B" slots and the Imac started posting again . I heard the chime and after refitting the Panel everything worked.
It´s sad that i can only use 2 of the 4 slots now, but im really happy i didn´t crash the entire system. After mounting the Ram i disassembled everything and fitted the NVME i bought. After a fresh install with Monterey the IMac runs incredibly good. It´s fine for me now. I watched a video where a guy removed only one broken pin from the socket and changed it with one from a donor board. Maybe, when i got time and enough skill, i will try it too.
Thanks again and have a nice evening

[moritz1992]

Re: iMac 27" Retina 5K i5 3.2Ghz no chime, no display, LED 1 and 2 on

Sorry i overread the question about why i removed the cpu..
Its just like i´ve never seen a cpu socket without any tool to hold the cpu in place. I did it many times and there is always a lever or something like that to push the cpu to the socket. In case of the IMac logicboard there is nothing like that, so when i pulled up the heatspreader the cpu comes with it and dropped after like an inch or so... Aplle Hardware is new to me. I will never do the same mistake again...