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A1418 / EMC 3069 / 2017 / 3.0 GHz quad-core i5, 3.4 GHz quad-core i5 or 3.6 GHz quad-core i7 Processor. Released June 8, 2017.

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iMac 2017 don't turn on after switching faulty HD to SSD

Some years ago I bought this iMac 2017 21.5” from second-hand. From day one it was super slow and almost unusable. After trial and error I figured it was a problem with its HD. I connected a SSD via USB to SATA to it, set it as the startup disk and it worked fine – except for the fact that it turned off frequently by itself and restarted. From time to time the startup disk preference was forgotten and it booted to its original HD, but I was able to revert startup back to SSD. At some point last year though after that happened I was never able to revert my startup disk to my SSD. It seems that it booted on its original HD and finally the faulty HD gave up and got corrupted. I wasn't able anymore to load macOS from its original HD and set my startup disk to my external SSD. I couldn't do anything besides opening it, remove the HD and switch to the SSD, which took me very long to do. I did that today and after replugging the monitor and plugging it to power, it wasn't turning on. I'm seeing only two LEDs after pressing the power button and the fan is turning on. According to this "Diagnostic LEDs" post it means that

  • "If LEDs 1 and 2 are on and LED 3 is off, then the backup battery (on the back of the logic board) may need to be reseated or the logic board may need replacement".
  • I also read that "Logic board diagnostic LEDs will not progress past LED 2 with a bad CPU".
  • And lastly "LED 3 Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then video card might be installed incorrectly or need replacement", however I'm not hearing the startup sound at all

I would like to try to figure out what might the issue. I've tried to turn it on with the SSD, went back with its faulty HD and with no HD / SSD. I'm always getting only LEDs 1 and 2 on. I never had any visual issues with its GPU (vertical or horizontal lines etc), but I was never really able to tell what was causing it to reboot itself since I started using it.

I'd greatly appreciate any help or suggestions on this. Thanks in advance!

Update (05/09/23)

@danj Hi, Dan! I just changed the iMac's battery but no dice. I still get LED 1 and 2 on, the fan spins, and nothing else. I tried with the display unplugged and plugged in. No chime sound. Is there anything else I could try? Does it make sense to try to connect to another monitor via USB c to HDMI? (In case I damaged the display connectors)

@danj I also considered doing a GPU reflow process, but since the GPU is integrated to the logic board in this iMac model, that doesn't make sense, right?

Video of the diagnostic LED:

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@thiagocapanema - Well that sucks ☹️

Let’s give this a try first disconnect the drive fully, see if that changes things. Then try connecting a external Monitor via HDMI.

I just can’t see how you killed your system.You did follow the iFixit guide to the letter and used the pizza cutter tool to cut the adhesive? If not you may have dated something that way.


@danj For the SSD upgrade and for the battery replacement I followed OWC guides on YouTube. I have all the tools available on iFixit iMac SSD Upgrade Kit. I used the pizza cutter to cut the display's adhesive. I didn't find that much difficult to change the battery and reassemble the iMac.


@danj What should I expect after turning it on without a HD? I just did that. One thing that changed after I replaced the battery is that after putting the plug in the outlet the two LEDs turns green and the fan starts spinning. If I hold the power button for 5s LED #2 turns off, then turns on again. If I hold power button for 10s only LED #1 is green

I reconnected the original HD to it and after turning the computer on the HD also turns on and starts spinning. I wanted to check if the HD was turning on since I can hear it as opposed to the SSD. I don't know if that means anything though


@thiagocapanema - Did you alter the RAM? See if reseating it solves this.

With a new drive it sometimes takes a bit of time for the firmware to realize there is no OS to boot from, even still you should see the icon on the screen.


Since I have nothing to lose, today I'll try to reflow the GPU using this method:


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Sounds like the button battery needs replacing that powers the NVRAM which holds the settings.

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Thanks, Dan! You're awesome and very helpful. Are you suggesting to do a PRAM Battery Replacement? I don't know if I can do it, but I'll follow this guide iMac Intel 21.5" Retina 4K Display (2017) PRAM Battery Replacement

I went only until step 27 on it. I'll report back. Thanks.


@thiagocapanema - Yes, the battery is used when the system is unplugged. It also is used when the outlet power switch is off.

Technically it’s an NVRAM based system from the older PRAM system. Basically, PAtato Vs POtato still it’s still the same in the end!

That explains the loss of settings. You may still have an issue as depending on what the system was running for macOS the system firmware may need updating this is because the file system was HFS+ and now APFS.


Just one thing, you're considering only the rebooting issue when you suggest to replace the battery, right? Right now I'm facing the two LED only issue though. Someone on reddit commented "did you practice proper ESD precaution when attempting to remove the old HDD from the iMac? If not then there’s a good chance that the MLB could have been damaged as a result of improper ESD safety. Since they’re sensitive materials, it could have damaged the board due to static electricity."

I didn't use an anti-static mat for this job and I'm afraid that maybe I damaged the logic board. If that's the case, there's nothing I can do, I'm in Brazil and this replacement would be costly prohibitive.


@thiagocapanema - Brazil is mostly humid, as such the risk from ESD is very low. So while that is an issue in dryer climates I wouldn’t assume that is the case here.

As far as the onboard LEDs. If you don’t have the display fully connected they can mislead you.

The needed battery is not very expensive, I would take the chance 😊


According to a technician on YouTube there's a 10% chance of solving this issue by replacing the PRAM battery ( The iMac that he's servicing had the same issue than mine, only two LEDs turning on. However this model was chiming and mine is not.

Someone from other forum suggested doing a "Command-Option-P-R" to reset the NVRAM. I connected a Windows USB keyboard to it, then I pressed "CTRL+ALT+P+R" for 20 seconds after pressing the power button. I tried that with the display attached and not attached. I don't think the system is starting up though, I don't hear any chime sound after turning it on, and the keyboard num lock light didn't turn on. I plugged the keyboard to my laptop and the numlock light turned on. I suppose the iMac is not reading the inputs from the keyboard.

I bought an anti-static wrist band and I'll use it to try to replace the battery later this week.


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Update (05/10/23)

After a new disassembly I reseated the RAMs

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I noticed that I was using a CR2025 battery (not 2032), I switched the Panasonic BR2032 back to the logic board (I tested it and it had some charge)

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I decided to remove the heat sink to reapply thermal paste to the GPU. I cleaned it up with isopropyl alcohol 99.8 and a paper towel

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I did the same to the CPU

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(I hope I the CPU is seated in the right position). I also bought a USB C to HDMI converter and plugged the iMac to the TV. I powered it on with SSD, HD and no drives. I got no image in the TV.

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Update (05/10/23)

I tried the GPU reflow route today since I had nothing left to lose. I followed this video: REFLOW GPU CHIP FIX BLACK SCREEN. I covered almost the whole logic board with 5 sheets of aluminum foil, exposing only the AMD GPU:

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For the reflow I followed this guide on reddit: Guide to perform a chipset reflow (0.2) [TechSupport|new_window=true].

  • Preheat at 180 °C for about 3 minutes
  • Crank the heatgun up to 220 °C
  • Point the gun about an inch away from the chip and heat for 1-2 minutes
  • Start dialing down the temperature of the heat gun
  • Keep going till you reach 40-50 °C on the heatgun
  • Let it cool for about 10 minutes

I used a Black & Decker heatgun to heat the GPU

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And a culinary thermometer to check the temperature:

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I reapplied thermal paste to the GPU and after reassembling the iMac.... No dice. I still have the same symptoms: Only LED #1 and #2 turns on, fan starts spinning, I can hear the original corrupted HD turning on and spinining if I connect it.

With that I think I tried everything in my power to get it back to life. A second hand model iMac 2017 21.5" is sold in Brazil for $800-1200 USD (I paid $1.500 USD at the time I bought it). I would love to be able to use it, with the 16 GB upgrade I did and with SSD it could be very useful for the next 5 years at least. I'm posting this in case someone with the same model faces the same in the future.

To sum up everything I tried to get this iMac back to life:

  • Changed corrupted original HD to SSD (then tried several scenarios, trying to turn it on without any drive, with the old drive etc)
  • Changed PRAM battery
  • Cleaned old thermal paste and applied new thermal paste to GPU/CPU
  • Bought a USB-C to HDMI dongle and tried to connect it to TV (no image is seen, I tried with no drives, with SSD and with old HD)
  • GPU reflow

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Thiago Capanema will be eternally grateful.
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