Late 2015 iMac 27 painfully slow / faulty

[MrHoobs]

Hi all, I recently sold my late 2015 iMac to my nephew. Worked fine when I sold it but 2 months later (typical) I’ve got it back to see if I can fix it for him.

Specs at the bottom of the post but it’s got a 2gb Fusion Drive. I THINK this might be the issue but wanted to get your advice before ripping it apart and replacing it!

It now takes a good 5-10 minutes to boot up, doesn’t always boot first time but restarts then boots up.

When I’m logged in, accessing even the basic things (settings, disk utility etc) take about 5 minutes each. I can’t open any decent apps as it just hangs.

I can’t update the iOS as it hangs at the ‘looking for updates’.

Also tried making a bootable SSD from my MacBook but the iMac doesn’t recognise it as a bootable disk. I thought this would at least help with troubleshooting.

Scouring this forum it sounds like it could be a fusion failure, so I might get a kit to replace with SSD.

Has anyone seen this before and either back my theory or tell me I’m going in the wrong direction please?

Thanks!

PROCESSOR 4OCH: QC 17, TBup to 42GH
MEMORY 1608 1867MH DOR 32. (2:868)
GRAPHIC AMD Radeon R9 M395X w4GB

 

[Nguyen Duc Hieu]

You can try the below to isolate the slow issue:

1. Buy a new external SSD (USB enclosure + SATA 2.5" SSD)
2. Install Mac OS on it (using your Macbook)
3. Plug it in the iMac 2015 and select it as boot device.

If this fixes your issue, you now can conclude that the internal Fushion drive is corrupted and need replaced.

I would just proceed with the disk replacement than wasting my time with diagnosis. It's so apparent.

 

[ignatius345]

Specs at the bottom of the post but it’s got a 2gb Fusion Drive. I THINK this might be the issue but wanted to get your advice before ripping it apart and replacing it!

Grab a copy of DriveDx and see what it says about the HDD and SSD portions of your Fusion Drive. It'll cost you all of 10 minutes. The demo mode will work for this, but it's worth paying for if you keep using it.

My old iMac 5K (2014) was starting to show some slowness and hanging, and DriveDx reported back that the 128 GB SSD part of the Fusion Drive was down to under 5% of lifetime remaining, worn out from just lots and lots of data being shuttled on and off it over the course of its life.

I got a kit from iFixit and opened the machine up, replaced the SATA hard drive with an SATA SSD. Not a super fun process but doable in an afternoon with the right tools and parts. Replacing that blade SSD would have been faster, but apprarently it's a bit of work to source the exact right one and replace it properly.* SATA was plug and play so I just went with that and left the 98% dead blade SSD inside. I think I got a couple more years out of it before replacing with an M1 iMac.

* Here's a thread about this: https://forums.macrumors.com/threads/a-list-of-successful-imac-27-2012-2019-ssd-upgrades.2162435/

 

[ignatius345]

You can try the below to isolate the slow issue:

1. Buy a new external SSD (USB enclosure + SATA 2.5" SSD)
2. Install Mac OS on it (using your Macbook)
3. Plug it in the iMac 2015 and select it as boot device.

If this fixes your issue, you now can conclude that the internal Fushion drive is corrupted and need replaced.

I would just proceed with the disk replacement than wasting my time with diagnosis. It's so apparent.

Diagnosis is like a 10 minute process.

 

[Fishrrman]

Sounds like the fusion drive may be having problems.
It could be the HDD portion (of the fusion drive) -- or the SSD portion.

Fastest, easiest, cheapest, SAFEST way to "work around" this:
As mentioned above, buy a USB3 SSD, and set that up to become the new EXTERNAL boot drive.

BEFORE YOU DO THAT
Try booting the iMac to INTERNET recovery.
This is NOT THE SAME as "the recovery partition".

Command-OPTION-R
at boot.
Keep holding that key combo down!

Ethernet works best for this. If connecting via wifi you'll need to enter your wifi password.
The internet utilities take a while to load, be patient as the globe spins.

When you get to the utilities, open disk utility.
If there's a view menu, go to it and choose "show all devices" (This is a VERY IMPORTANT step).
First thing I'd try is the "first aid" option.
Try it on EVERY volume/partition/etc. -- "from the top down".

Do you get a good report?

If so, next thing to try is a "safe boot":
Reboot, hold down the shift key CONTINUOUSLY until just before login.

Can you get booted?

If you are encountering problems waiting for "updates" that won't download or install, I'd suggest you go to the software update pref pane and DISABLE all automatic updates.
Things just work better that way.

 

[Nguyen Duc Hieu]

Diagnosis is like a 10 minute process.

Didn't you read his post describing the issue?
5-10 minutes to boot up
5 minutes to complete a single task like opening any app.

I would bet that it would take him more than an hour to download the app you mention about and run the test, if his iMac ever let him do that at all.

And what's that for? Same result that the Fusion drive has gone bad and need replacement.
Why bother spending hours running diagnosis to acquire the known result?

 

[ignatius345]

Didn't you read his post describing the issue?
5-10 minutes to boot up
5 minutes to complete a single task like opening any app.

I would bet that it would take him more than an hour to download the app you mention about and run the test, if his iMac ever let him do that at all.

And what's that for? Same result that the Fusion drive has gone bad and need replacement.
Why bother spending hours running diagnosis to acquire the known result?

OK, embarrassingly I had skimmed the post and missed what you point out. My bad.

It does sound pretty severe and like a routine disk check might take ages and/or just fail.

 

[MrHoobs]

Thanks all for the amazing replies.

Being a skinflint I’ve spent the day trying not to spend any money 😂

I have a 512gb SSD and have been trying without success to make an external HDD.

Problem is you need a Mac with the same OS, the iMac can only go to monterrey I think and my MacBook is on the latest. So when you try and make a downgraded software drive it won’t let you!

Then I turned to try and make a recovery disk from the iMac, or run disk utility, or get to the terminal. Anything! I can click an application, then it hangs for 5 mins and reboot. I can’t even open the settings pane let alone the App Store.

So I can’t even make an external ssd boot drive, I’m going to have to bite the bullet and buy an ssd kit from ifixit or Amazon.

Trying to avoid this as a) cost but b) my cackhandedness that is likely to break the screen 🤦🏻‍♂️.

I’ll just buy a 512gb disk then hopefully I can set up the old fusion as extra storage.

Hey. What’s the worst that could happen 😂

Thanks again for the info, really appreciate it

 

[Nguyen Duc Hieu]

Thanks all for the amazing replies.

Being a skinflint I’ve spent the day trying not to spend any money 😂

I have a 512gb SSD and have been trying without success to make an external HDD.

Problem is you need a Mac with the same OS, the iMac can only go to monterrey I think and my MacBook is on the latest. So when you try and make a downgraded software drive it won’t let you!

Then I turned to try and make a recovery disk from the iMac, or run disk utility, or get to the terminal. Anything! I can click an application, then it hangs for 5 mins and reboot. I can’t even open the settings pane let alone the App Store.

So I can’t even make an external ssd boot drive, I’m going to have to bite the bullet and buy an ssd kit from ifixit or Amazon.

Trying to avoid this as a) cost but b) my cackhandedness that is likely to break the screen 🤦🏻‍♂️.

I’ll just buy a 512gb disk then hopefully I can set up the old fusion as extra storage.

Hey. What’s the worst that could happen 😂

Thanks again for the info, really appreciate it

You haven't tried the guide from Fishrrman above?
Internet recovery is an interesting solution. I assume that it can install Mac OS on your external SSD.
If you already have an SSD and a USB enclosure lying around, I suggest you try it.

Furthermore, if you want to create a USB installer of Mac OS Monterey on a Ventura operating Macbook, you can try Opencore Legacy Patcher(OCLP). In OCLP menu, there is an option that enables you to download and create a USB installer of Big Sur or Monterey, Ventura without the limitation of exising Mac OS version.

If you don't mind spending some time to read, OCLP guideline is here

OpenCore Legacy Patcher

Experience macOS just like before

dortania.github.io

Link to download

Releases · dortania/OpenCore-Legacy-Patcher

Experience macOS just like before. Contribute to dortania/OpenCore-Legacy-Patcher development by creating an account on GitHub.

github.com

 

[MrHoobs]

Ok so just tried using my sisters old air that has sierra on it.

Managed to get high sierra on as a bootable disk; got as far as selecting the SD card as a drive, it gets so far but needs to reboot, by which time the iMac tries to reboot the main Fusion Drive.

Is there a way to disable the fusion? If it boot mode I do get as far as disk utility, but when I select erase of the fusion the delete progress bar hangs, I’ve waited for an hour but no progress.

I’ve tried unmounting but they didn’t work. Surely I must be able to disable it so when the iMac reboots it only sees the sd card it’s installing on?

Will take a look at the OCLP too thanks!

 

[Fishrrman]

Power off, all the way off.

Put your finger on the option key and KEEP HOLDING IT DOWN as you press the power on button. Keep holding down the option key.

Do you get to the startup manager?

If so, select the SSD with the pointer and hit return.

Do you get a "good boot"?

If so, open the startup disk preference pane.
Click the lock on the bottom and enter your password.
Now click the icon for the external SSD, then close the pane.

NOW try another reboot.
You should boot directly to the SSD.

Does this work?

If it does, good.
More....

When you boot from the SSD to the finder, do you see the internal fusion drive on the desktop?
If so, can you access files on it?
If so, now's the time to get them copied to a backup, somewhere else.

Once you get everything off the fusion drive, you can use disk utility to
- erase it
or
- "break" the fusion (into separate SSD and HDD portions)
then
- erase the internal SSD and HDD
then
- just "leave them there, unused", or perhaps use the HDD for storage.

 

[MrHoobs]

Thanks again everyone - finally got a version of high sierra installed on an external SSD card. Booted the iMac up using that and it works a treat!

Still can’t do anything with the Fusion Drive; it shows up in disk utility but can’t erase, unmount or save anything to it. I’d say it’s pretty much shot.

At least I can add a new internal ssd now and get it working again for my nephew.

Tip: never sell second hand electrical to family it’ll bite you in the ass 😂.

 

[Nguyen Duc Hieu]

Thanks again everyone - finally got a version of high sierra installed on an external SSD card. Booted the iMac up using that and it works a treat!

Still can’t do anything with the Fusion Drive; it shows up in disk utility but can’t erase, unmount or save anything to it. I’d say it’s pretty much shot.

At least I can add a new internal ssd now and get it working again for my nephew.

Tip: never sell second hand electrical to family it’ll bite you in the ass 😂.

Is there anything to do with the FileVault setting?