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Model A1419 / EMC 3070 / Mid 2017 / 3.4, 3.5 or 3.8 GHz Core i5 or 4.2 GHz Core i7 Kaby Lake Processor (ID iMac18,3) / Retina 5K display. Refer to the older iMac Intel 27" Retina 5K Display (Late 2014 & 2015) guides as the system is very similar.

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No startup after CPU and SSD replacement, diagnostic LED confusion

2017 iMac 27 Retina 5K, i5 3.8, 8GB VRAM EMC 3070

I just swapped my CPU to the 7700K and changed out the SSD to a Feather Turbo 1GB. The Feather is supposedly loaded with High Sierra and listed to be compatible. The HDD is wiped and formatted. Expected to boot into a restore or have to restore from USB.

Followed the documented procedures and everything seemed to go well. Go to power up and nothing happens. Pull off the glass and find the diagnostic LEDs. There are FIVE.

Plugged in, there is definitely power. LED 1 lights up green and steady.

When I push the power button though, LED 1 just blinks as long as I am holding it down. When I release, LED 1 is steady. Nothing happens beyond that when I push the power button. I removed and checked the powder supply to ensure all connections were secure; they were and the problem persists.

I have looked around a ton now and cannot seem to find any reference to a blinking or flashing LED 1 when the power button is depressed. LED 2 does not come on at any time.

I can find the basics on the LED meanings for the main FOUR but this is not covered and nothing seems to be said about the fifth one.

Any ideas? Does this sound like a PSU or Logic Board issue here?


Update (09/20/2019)

Tore it back down and in the process of reattaching the heat sink and that insanely overbowed tension spring, I had accidentally unseated the CPU.

Unfortunately, this also seemed to bend a single pin in the socket. With some phone magnification and a needle, I managed to get it back in what appears to be a reasonable orientation and think it might be OK.

I won’t be able to test as in the process of removing the heatsink, the processor delidded (I bought it used, previous owner had already delidded and added liquid metal, but it appears the reseal was weak), SO, now I have to wait for a rocket 88, and some Grizzly Cryonaut and Conductonaut to arrive Monday to repair the delidded CPU before I can put things back together and see if that socket pin is OK.

Pretty likely that this is why I never got the 2nd LED to light. At least I hope so…CPU was almost certainly unseated….definitely cockeyed when I opened it up and was careful to note that....will have to see once I get the parts sorted.

Update #2 (09/20/2019)

Re-lidded the processor (Used Conductonaut, for now I am not going to concern myself on the long term implications of that).

Reassembled everything and was very cautious to maintain the alignment of the CPU in the socket. I also managed to realign the bent pin to a point where it appears to be nearly indistinguishable from the surrounding pins, so hopefully we are going to be ok there.

After reassembly, I now get diagnostic LED 2 to illuminate, but no further. Fan starts spinning and you can hear the HDD spin-up and the head moving. There are no chimes and there is nothing on the screen.

The Feather SSD is supposedly loaded with High SIerra so it should boot. It did not. I tried booting into recovery mode, safe mode and off of a USB with the Mojave installer and it will not recognize anything. I installed Mojave’s in full on the HDD and tried that, nothing.

Keyboard does not seem to connect, no power on caps lock light even when connected by cable, maybe Inhibiting recovery boot cmd?

Beantwoord! View the answer Dit probleem heb ik ook

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@drdavebourgouin - Time to put back the original CPU to see it the logic board is still working.


Indeed, that’s today’s project. Thanks Dan...will update on the results. Fingers crossed!


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Reinstalled the i5 and all is functional again. Looks like I killed the 7700k with my mistake or it was DOA when I got it.

Logic board diagnostic LEDs will not progress past LED 2 with a bad CPU.

Fledgling Feather Turbo SSD working perfectly. Looks to be a great option for PCIe blade upgrade.

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Not good ;-{

Clearly you’ll need to get a real virgin CPU Vs a hand me down. As clearly that’s cost you! Between the damage and the risk of the liquid metal dripping as the chip orientation on edge puts this in a direction that over time will fail from gravity pulling on the liquid metal as it heats it gets thinner! Loosing its adhesion to the chip and its lid surface.

Don’t get me wrong I have no issue using liquid metal! As long at the chip is flat not on its edge as well as on desktops not laptops.

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Thanks for the reply. Never considered the orientation and potential leakage of LM from a vertical processor...still working on this one, update to the thread.


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This is a good lesson for those who believe they can “save a few bucks,” as I did repeatedly when I was young and had more initiative than brains.. I was proud of not being a quitter, but really I was just slow learner at times. Stubbornness = ignorance and pride. That lil’ combo is downright dangerous. Many times it actually costs you much more than if you spent the money upfront the first time and just bought the best. I learned this from buying basses. I bought 4 or 5 basses that were ok, but every one ended up having some issue. I knew I should just buy a Fender P bass and get it over with, but no. I bought a Gibson EB3 instead. The night before our biggest gig to date, it shorted and squealed in the middle of a song. l lifted it over my head and in the way of the “Who,” slammed it on the concrete floor breaking the neck into 3 pieces. The band looked at me, and said, “so whatcha gonna do now,” laughing at me. The next morning I went to the music store and bought that P bass. That was 1973. I paid $325 for it. Today it’s worth about $3k, and it’s never broke, always sounds perfect and alive and people specifically ask for that bass on gigs. I spent probably $1000-$1200 on basses that didn’t do the job I needed them to, when I could have saved that money and been happy all those years. Lesson learned, happily:). Now, when I want something, I research first, then. try it, then buy the best one possible, and here’s the beauty of it. I always go 2 steps up from what I believe I can afford, and somehow it always works out. Being flexible, having a can do positive attitude, being teachable, and looking for options while working as a team with the salesman, instead of against him will yield amazing results.

Btw @drdavebourgouin, MacRumors has a thread on upgrading your iMac’s CPU and ssd, if you don’t know. Many great tips and problems solved on that thread.

Good luck. I just thought there are so many young people doing these repairs, I don’t want them falling into my behaviors, so the commentary, please forgive me, if this isn,’t you:), haha.

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I’m absolutely no novice at this, having upgraded the hardware in iMacs before. I have done a pile of research in advance, including that thread you posted. This was not about taking a cheap approach to boost the system, it was a reasonable project for me and something that I wanted to take on as I enjoy these kinds of things. Clearly something went wrong and I made a mistake. I can deal with that. I’m taking a systematic approach to correcting the problem. I’m just here looking for opinions of those who have more experience than I with these systems.

Thanks for your perspective.


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drdavebourgouin zal eeuwig dankbaar zijn.

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