SATA Cable or Controller Failure in Late 2015 27” iMac Retina (A1419 EMC 2834)?

[Malagutial]

Hello! I have been tearing my hair out over this repair, so I’d be grateful for any advice you can give.

My Mum’s iMac was running poorly for several months - it took ages to boot, and would hang on the spinning wheel between every operation. Eventually, it refused to boot (kernel panic I think). I booted into recovery mode, and was unable to repair the drive, either through disk utility or command line. I figured we had a bad drive and decided to replace it and upgrade to an SSD at the same time.

I bought the repair kit, including the sensor cable and a 3.5-2.5” bay adapter. Important detail - I formatted the new 960gb SSD with my MacBook Pro via a USB adapter. I then installed it into the iMac, put the machine back together and booted it into the Mojave installer via USB. Mojave installed onto the single partition I had created from the MacBook, and it ran perfectly. I figured everything was sorted, so I left the iMac on overnight to transfer some files (which I had recovered from the old drive).

The next morning, I came down to find the iMac running on a black screen. I can only assumed it had restarted to install an update. I forced it to reboot, and I was presented with the ‘prohibited’ symbol. I booted into internet recovery mode and tried to repair the drive, which failed. I then tried to erase the drive, which also failed. I tried to partition the drive - that failed too.
Next, I tried booting into TechTool’s diagnostic software, which told me the disk passed SMART testing, but did nothing else to fix it.

Next, I reinstalled Mojave onto an external drive, booted from that, and tried to erase/partition the internal SSD through disk utility. That failed every time too. I then ran DiskWarrior, which told me the disk was badly corrupted and couldn’t be fixed.
This surprised me, as it was a brand new disk which appeared to work fine. So I gritted my teeth and cut the iMac open again.

I hooked the internal SSD back up to my MacBook again using a USB adapter which was itself connected to the sensor cable attached to the SSD. I opened disk utility, and, to my amazement, I was able to perform all operations on the SSD - erase, partition etc.

This led me to believe that the problem does not lie with the SSD or the sensor cable, but with either the SATA cable or the SATA controller in the iMac. To test this, I connected the SSD back to the iMac, reconnected the screen (no adhesive), and booted into a Mojave installer USB. As when I had first installed it, the computer recognised the SSD and the ‘Macintosh HD’ Volume I had just created from my MacBook. I tried erasing that volume from the iMac and it once again failed in precisely the same ways. I reconnected the drive to my MacBook via USB, and it erased with no issues.

Therefore, it seems reasonable to conclude that there is something unique to this iMac which makes it unable to erase/partition this drive. I think that this can only be either: The SATA cable (defective or poorly seated), or the SATA controller.

Are either of these known/likely failures in iMacs like this one? Can anyone advise on what the problem is most likely to be?

Thanks in advance!

Alex

 

[MacInWin]

Welcome to the Forum, Alex. And let me say that it's very nice of you to be "tech support" for your Mum!

As for your problem, I can't tell you how to determine which is bad, but the cable is certainly much less expensive to replace. Cables can become brittle over time and movement (unplugging, plugging, etc), can break the conductors easily. So the most inexpensive path is to replace the cable first, see if that solves the issue, and if not, then look at what has to be done to replace the drive controller. It may entail replacing the entire logic board. I don't know if that is necessary, but take a look at what ifixit.com has on that particular iMac. If there is a separate drive controller board, that could be the next thing to look at, after the cable.

Finally, depending on how your Mum uses the iMac, it may be an option to put the new SSD in an enclosure and let it boot from there. IF she doesn't boot that often, just lets the iMac sleep when not using it, then the performance may be acceptable that way.

 

[Malagutial]

Welcome to the Forum, Alex. And let me say that it's very nice of you to be "tech support" for your Mum!

As for your problem, I can't tell you how to determine which is bad, but the cable is certainly much less expensive to replace. Cables can become brittle over time and movement (unplugging, plugging, etc), can break the conductors easily. So the most inexpensive path is to replace the cable first, see if that solves the issue, and if not, then look at what has to be done to replace the drive controller. It may entail replacing the entire logic board. I don't know if that is necessary, but take a look at what ifixit.com has on that particular iMac. If there is a separate drive controller board, that could be the next thing to look at, after the cable.

Finally, depending on how your Mum uses the iMac, it may be an option to put the new SSD in an enclosure and let it boot from there. IF she doesn't boot that often, just lets the iMac sleep when not using it, then the performance may be acceptable that way.

Hi Jake,

Thank you so much for your kind words. Unfortunately, I’m the only person able to act as tech support for Mum these days, so I take the role very seriously!

I couldn’t leave this to rest, so I connected the screen back up to the iMac and propped it open, allowing me to try new things and test more easily. I decided I should see whether a different drive would work, so I removed the SATA cable and sensor cable from the SSD mounted into the iMac, and hooked them both up to an old 2.5” platter drive I had lying around. To my amazement, the iMac was able to format it with no issues, and that made me wonder whether it was simply the positioning of the cables that was causing all the trouble. After all, you need to do a bit of twisting in order to get the original SATA cable and the sensor cable in. So, with the screen still propped up, giving me lots of space to work, I connected the cables ‘loosely’ to the SSD, avoiding any kinks or twists, and letting the cables fall where they wanted. Lo and behold, it worked! Disk utility could format the SSD via the internal SATA connection. This means it is almost certainly the SATA cable which is to blame; it’s damaged in such a way that it only works in certain positions.

Since I figured this might be the problem, I had the foresight to order a new one much earlier today, so it should be with me tomorrow thanks to next day delivery. I’ll fit it, switch to a different drive bay adapter that should put less strain on the cables, then try again tomorrow. I’ll post my results here!

I’m pleased to have figured this out (fingers crossed), but I’m still curious as to whether anyone else has had this issue? This iMac has never been apart, so this cable has never had any reason to move. That suggests it might have been defective from new...

Best wishes,

Alex

 

[chscag]

I’m pleased to have figured this out (fingers crossed), but I’m still curious as to whether anyone else has had this issue? This iMac has never been apart, so this cable has never had any reason to move. That suggests it might have been defective from new...

As a matter of fact, one of our Administrators experienced a bad SATA cable in an iMac he owns. He too had to go thru some various fixes before it became apparent it was the cable. Perhaps he will tune in here and give you some first hand advice.

Anyway, please keep us informed when the new cable arrives. And thanks for using our forums.

 

[MacInWin]

Good job, Alex! The cable suffers from degradation from heat, becoming brittle, so that it takes very little movement to create a hairline crack in the cable that only manifests when the cable is in certain positions, or under strain. You seemed to say the cable had some strain on it, which can pull the hairline crack apart, leading to failure. So a new cable will be more flexible, you can install it and it should last until the next time you have to open the iMac (hopefully, never).

 

[Malagutial]

As a matter of fact, one of our Administrators experienced a bad SATA cable in an iMac he owns. He too had to go thru some various fixes before it became apparent it was the cable. Perhaps he will tune in here and give you some first hand advice.

Anyway, please keep us informed when the new cable arrives. And thanks for using our forums.

An update for both of the people who very kindly offered their thoughts:

I fixed the iMac, and I can confirm that it was a faulty SATA cable. The repair was a complete pain, because I had to remove almost every component from the machine in order to get to the other ends of the SATA cable. However, I have two tips for anybody else considering a SATA cable replacement:

(1) The iFixit guide instructs you to remove the logic board in order to change the SATA cable, but you can actually change the cable by removing only the right speaker and the main fan/vent above the logic board. The clip for the power section of the cable is easily accessible - you can pull it out with your fingers. The SATA connector is harder to get to, but I used some angled medical forceps to pull the cable down and out. It’s harder getting the new cables in, but the angled forceps can be used to clip the SATA connector into place. Use a little mirror to look at the socket for the power clip, and you’ll be able to see which way round it goes. Like I say, it is a little fiddly, but it saves an enormous amount of time/risk compared to removing the entire logic board and everything connected to it!

(2) I think the design of the OWC sensor cable is bad, to the extent that it requires you to bend it/the Apple SATA cable to make them fit it. That’s not just me - it’s part of the guide from iFixit and Flexx. The Apple SATA cables seem prone to failure, so I don’t think it’s a good idea to leave them under stress inside the (hot) iMac. I mitigated against this problem by modifying the 3.5-2.5” hard drive bay adapter so that the SSD (and by extension it’s connectors) sits lower down in the space typically occupied by the 3.5” drive. This allows the SSD, sensor cable, and Apple SATA cable to sit in a nice straight line, with none of the cables under any stress. See the attached picture. I highly recommend this to anybody replacing their HDD with an SSD or other 2.5” drive requiring the OWC sensor cable.



Thanks to both of you for chipping in. I really hope this thread helps somebody else!

Alex

 

[chscag]

Nice work and well done! We appreciate you posting back and showing us how things went. Great tip about not having to remove the logic board.