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

[tcapanema]

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.

1. It was suggested to me that since I didn't practice proper ESD precaution when attempting to remove the old HDD from the iMac I could have damaged the logic board due to static electricity.

2. Another suggestion was to try a PRAM Battery Replacement, but I'm not very keen to unmount the whole logic board and replace the battery if there's not a good chance of it solving the problem.

I'm in Brazil (no AppleCare or official Apple support here) and a logic board replacement from an assistance or even importing the logic board and doing it myself would be costly prohibitive.


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

 

[rpmurray]

2. Another suggestion was to try a PRAM Battery Replacement, but I'm not very keen to unmount the whole logic board and replace the battery if there's not a good chance of it solving the problem.

The symptom of the iMac forgetting the startup disk setting does suggest that the battery may be dead. When you were seeing this, did you also need to change the time and date after getting it to boot?

 

[tcapanema]

The symptom of the iMac forgetting the startup disk setting does suggest that the battery may be dead. When you were seeing this, did you also need to change the time and date after getting it to boot?

No need to change date and time... I guess. If that was the case I should've seen this issue on both macOS installs? I had one macOS installation in the hard drive inside it and another one on the external SSD. I can't recall if there was an issue with date and time on the hard drive installation (the date / time isn't updated from the internet?). I never had date/time issues on the SSD macOS install.

 

[rpmurray]

From what I understand the battery powers the real time clock in the iMac. My thought was that if it was dead then the clock would be resetting to some default date. But you're right, once the iMac boots up the clock would be synced with real time via whatever time server is set up in the date and time system settings, if you have it connected to the internet via WiFi or ethernet. Was just trying to think of a way to determine if the battery was really dead, since it could be a reason why you're having this problem.

 

[tcapanema]

From what I understand the battery powers the real time clock in the iMac. My thought was that if it was dead then the clock would be resetting to some default date. But you're right, once the iMac boots up the clock would be synced with real time via whatever time server is set up in the date and time system settings, if you have it connected to the internet via WiFi or ethernet. Was just trying to think of a way to determine if the battery was really dead, since it could be a reason why you're having this problem.

Thanks for replying. According to this technician 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: 2014 iMac Chime Black screen No startup PRAM Battery replacement -- However this model was chiming and mine is not. I think I'll give it a try, but now I need to purchase an antistatic mat to work on it and get to battery.

 

[rpmurray]

Before you go to all this trouble, have you tried doing a Command-Option-P-R to reset the NVRAM? How to reset the NVRAM, PRAM, and SMC on any Mac.

 

[tcapanema]

Before you go to all this trouble, have you tried doing a Command-Option-P-R to reset the NVRAM? How to reset the NVRAM, PRAM, and SMC on any Mac.

No, I didn't try that. I tried now, but no success. 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 screen 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.

On logic board: LED 1 turns on after plugging it to power. After pressing the power button LED 2 turns on and stays on and the fan starts spinning. I can't get past that.

 

[tcapanema]

I tried the NVRAM reset again twice by pressing "WIN + ALT + P + R". I tried using the Magic keyboard also, but it's wireless and there's no visual indication that it's working, I don't even know if it is charged. I plugged it in the outlet and left it there for a day, but I still don't know if it's charged. I don't know if charging works on it with a wall charger.

 

[tcapanema]

Here's the diagnostic LEDs video of my iMac 2017, 21.5-inch, 2017, 4K issue

• LED 1 turns on with the power cable connected
• LED 2 turn on after power button is pressed and the fan starts pin
• There's no chime sound after that
• I checked this scenario with the display connected and disconnected

I just dismantled it almost completely for a PRAM battery replacement. Originally it comes with a Panasonic BR2032, but I couldn't find one in Brazil and found only one seller on eBay that ships them internationally (from Germany). I didn't want to wait for months just to get this battery, so I replaced it with a new Panasonic CR2032. I had two Crucial 8GB RAMs that I bought long time ago so I also did a RAM upgrade. After reassembling it, no dice, I'm having the same issue as before (see video above).

I'm out of options right now since this indicates a GPU failure, which is weird, since I never had any visual GPU issues while using it. I guess that the computer auto-rebooting could be a symptom of GPU failure, though. There are many reports of similar incidents on iMacs rebooting by itself / constant crashes / kernel panic.

I just 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.

 

[tcapanema]

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:

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

• 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

And a culinary thermometer to check for the temperature:

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