The ordeal of DIY iMac upgrade

Last two days was an ordeal for me, I upgraded my Late 2015 5K iMac that originally came with Intel Core i5-6500 processor, the infamous 1 TB Fusion Drive with 24 GB of NVME SSD storage and 1TB of spinning hard drive (Apple, this is a crime), AMD Radeon R9 M390 2GB graphics.

This model of Mac should be more than adequate for most users if Apple didn’t do the whole Fusion Drive thing. Fusion Drive is Apple’s way of combining SSD to a traditional spinning hard drive. When this concept was first introduced by Phil Schiller, the 1TB option paired a 128 GB SSD with a 1 TB 5400 rpm spinning hard drive, and in the 2nd iteration, Apple being Apple, slims down the 128 GB to merely 24 GB. This change made iMac unusable, for most cases, slow disk speed is the bottleneck. So I decided to upgrade the 24 GB blade SSD to a 500 GB Samsung 750 EVO.

The parts I got was:

  1. Samsung 970 EVO SSD 500GB – M.2 NVMe Interface Internal Solid State Drive with V-NAND Technology (MZ-V7E500BW), Black/Red.
  2. Sintech NGFF M.2 nVME SSD Adapter Card for Upgrade MacBook Air(2013-2016 Year) and Mac PRO(Late 2013-2015 Year) Note: The model number for this unit is ST-NGFF2013, they also have ST-NGFF2013-C with the same port but better insulation and a back panel to support the SSD.
  3. Intel Core i7-6700K CPU (used unit from eBay).

The tools and I got was:

  1. Apple 6pcs iMac LCD Screen Adhesive Open/Cut Wheel Tool 21.5” A1418 & 27” A1419 (eBay Link). Note: not really necessary if you have a pizza cutter, but be careful if you use actual pizza cutter, you do not want to insert it too deep to cut the cable.
  2. Apple 076-00009 Adhesive/Tape Repair Kit for iMac 27” Retina Late 2014-2015 (eBay Link).
  3. Apple 944-4365 iMac Display Service Wedge 21.5” A1418 & 27” A1419 2012-2019 (eBay Link). Note: Completely unnecessary.

I did ample research on the entire process, but the whole thing still became an ordeal, while I was doing it, I kind of wished I never had the idea of CPU upgrade in the first place. I’ll elaborate, but before that, the tutorials I followed were:

  1. iFixit: iMac Intel 27″ Retina 5K Display Blade SSD Replacement.
  2. iFixit: iMac Intel 27″ Retina 5K Display CPU Replacement.
  3. iFixit: iMac Intel 27″ Retina 5K Display Adhesive Strip Replacement.
  4. MacRumors: A list of successful iMac 27″ (2012-2019) SSD upgrades.
  5. MacRumors: iMac (Retina 5K, 27-inch, 2017) CPU and NVME SSD Upgrade Pitfalls and Tips

These tutorials and online forum posts were really helpful. I don’t want to repeat what they have said, so the main obstacle I met were:

Broken power button cable when getting the left speaker out.

This is me being not careful and too agitated in cracking the whole thing open. In the iFixit guide, they specifically said to be careful not to rip the cable off. In order to fix this, you need to use a heat gun (or hairdryer) to heat up the adhesives on the power button. Solder the wire back together and stick the power button back. It’s worth noting that the power button send signal 1 (two cables connected) to the power supply when pressed.

CPU metal bracket and the effect of unsecured CPU

So this was the main thing that I wish I knew before I decided I can do the CPU upgrade. It haunted me for 12 hours straight, and it’s all because of this metal bracket.

Loaded CPU bracket on the back of the motherboard. Photo Credit: me.
CPU bracket picture from MacRumors user sebastienc

When you place the CPU on the LGA 1151 connector on the motherboard, the CPU is not secured on board at all. When you put the heat sink on the CPU with thermal paste, the CPU will be picked up by the heat sink, when you load the metal bracket on the back side of the motherboard, the CPU will have a chance to slip a bit and misalign. If you failed to notice the unevenness of the heat sink and keep loading the bracket, the PCB board on the CPU will be bent and you will be damaging the LGA 1151 connector.

But how do you tell whether you have the CPU properly installed? What will the system behave when you try to boot it up with a not properly installed CPU? For me, I have two kinds of behaviors: (Note: about diagnostic LEDs and diagnostic ports on the mother board, there are plenty of documents easy to find on the internet)

1. The diagnostic LED 1 on the motherboard lights up when I connected the iMac to power, LED 2 3 and 4 was off and remained off when I pressed the power button. In this case, the power button was okay, the power supply unit (PSU) was okay, the control cable between PSU and motherboard was okay, the diagnostic terminal on the motherboard could not read 12V signal between port 1 (GND) and port 11 (power up signal).

2. The diagnostic LED 1 and 2 was on when I connected the iMac to power, the fan starts to spinning low speed, the LED 2 may briefly turn off and went on again even without pressing the power button, the fan is spinning up till its at full speed. The diagnostic terminal reads 12V between port 1 (GND) and port 11 (power up signal)

For case 1, its tempting to replace the PSU because according to the diagnostic LED, PSU is having trouble sending power up signal to the motherboard. For case 2, it’s really strange but we can tell its a CPU problem, because no LED 3 means motherboard is not talking to the graphics card, and the CPU should have working graphics card. Could it be a motherboard issue? I really don’t know.

These scenarios were rarely discussed online, I was panicking for few hours before I saw sebastienc’s reply on MacRumors. In one particular entry, he said:

Getting LED 1 or LED 1-2 both means CPU issue. Ultra fan speed also was due to that…

So I recollected myself and started to take the CPU off the motherboard, only to found out that the PCB is slightly bent and the CPU moved a little bit to the right, the CPU had connection issue. Some of the LGA 1151 pins are slightly bent. I spent few hours straighten them out and reloaded the CPU, put everything back and plugged in the power again.

The LED 1 is on…

The LED 2 is on… (wait, I didn’t even press the button yet wtf did I fail again)

The fan starts to spinning up. (oh that can’t be good, I am going to press the power button because why not)

The LED 1 is on, LED 2 is on, a dimmed LED 3 is on?

I heard the power chime. The fan is still spinning like crazy but I figured that’s because I haven’t connect the hard drive and the hard drive thermal sensor yet.

The rest was a blur, by that time I was 18 hours in this project and I haven’t ate anything for more than 24 hours. Before that power chime, I was worried and I was broke, I checked prices for PSU, for new mother board, for new Mac Pro (haha), and I checked my bank balance.

The outcome

After macOS reinstallation, the system is super fast and I can feel it. The SSD benchmark is blazing fast. TRIM is automatically enabled and the drive is operating under X4 link width. The only catch is, I have to set the hibernate more to 25 to be able to resume properly from sleep (for 2017 iMacs and later models, you don’t need to do this), the command is: sudo pmset -a hibernatemode 25 standby 0

For the CPU part, I didn’t really experience much difference cause CPU was honestly not the bottleneck of this machine, I still ran a few benches nonetheless, the CPU temperature is hotter to my taste but I could not be bothered to go through that process again if I don’t have to, so I’ll leave it as it is.

This project was challenging and I thought I did pretty good research beforehand, turns out it was way harder than I thought, in hindsight, I wish I stopped when I installed the NVME drive, the CPU upgrade was waaaay harder. I don’t think I want to do this in the future. It was fun, but the uncertainty and the amount of mental stress I have been through was not good.

I understood that people may have the same issue, and I hope my article can shed some light in your situation, and I sure hope Google can take you to the right place. For me, if I didn’t read the post from sebastienc, I would order a new PSU and wasted bunch of money already.

If you have any questions, feel free to comment or to contact me and I will be very happy to help you with that.