Constant Freezing and Restarts - iMac (Retina 5K, 27-inch, Late 2014)

Discussion in 'Mac Basics and Help' started by tomantrim, Oct 15, 2016.

  1. tomantrim macrumors newbie

    Oct 15, 2016
    I have an iMac that is essentially unusable due to constant freezing and restarts. The frequency can be multiple times per hour and it seems to happen more often when video or images are being displayed in a browser window. I am currently running macOS Sierra, but experienced the issue under El Capitan and Yosemite when they were installed. It feels as though the issue has increased in frequency over the past year, but I did not keep count. The frequency started to occur enough that I gave up trying to live with it and decided to contact support. I was hopeful that Sierra would fix the issue, but that was not the case.

    As you'll see below, I have contacted support and dropped the computer off at the Apple Store, but Apple states there is no problem. After doing my own troubleshooting based on research in various forums, I am posting this as my last gasp hope that someone has a silver bullet that fixes this crippling issue. If I can not find a fix, then my only recourse is to contact Apple to return the computer for a full refund, or get them agree to replace the computer with a new, working model. Curious if anyone has had success with this approach for this model of iMac after experiencing similar issues.

    Thank you in advanced for your assistance. I am open to all suggestions at this point. If you need more information please let me know and I’ll do my best to provide it as quickly as possible.


    Behavior and Symptoms Experienced:
    • Computer will freeze and all windows and menus become unresponsive. Most of the time I can still move the cursor around on the screen, but that is the only aspect of the system that seems to work. If there is music/audio playing it will continue to play uninterrupted. After 1-3 minutes the windows/menus become responsive again and I can continue to use the computer.
    • Computer will freeze as described above, but never becomes responsive again and eventually restarts to the login screen. The user account has been logged out in this case. After I login again, the computer seems to work normally again until the freezing occurs again.
    • Computer will freeze as described above, but never becomes responsive again and eventually goes to a black screen and the computer restarts displaying the Apple logo and progress bar.
    • Periodically when the computer freezes and prior to restarting the fan can be heard spinning up and becomes very loud. In this case, it usually goes to the black screen described above before rebooting.
    • In some cases when the computer freezes portions of the screen turn bright red and the windows appear to break apart and are displayed in a fragmented fashion. Today, I was able to capture an example of this with my iPhone in the attached picture. There are two Safari browser windows in the picture attached and the bright red displayed was not part of the original web pages.


    Troubleshooting Completed To Date:

    Apple Support:

    • Contacted Apple Support last weekend and spent ~4 hours with two different reps via chat. During the chat session I mentioned I had read that some iMac's have had a problem with the graphics card and needed to have them replaced. Apple Support stated that most often it is just a software issue. They had me perform the following troubleshooting steps.
    • SMC Reset
    • NVRAM/PRAM Reset
    • Logged into my user account
    • Used computer for ~5 minutes
    • Experienced the issue
    • Created new TEST account
    • Logged into the TEST account
    • Used computer for ~5 minutes
    • Experienced the issue
    • Booted into OS X Recovery via Command-R
    • Ran First Aid on Macintosh HD
    • First Aid completed without any errors
    • Logged into my user account
    • Used computer for ~5 minutes
    • Experienced the issue
    • Booted into OS X Recovery
    • Selected "Reinstall MacOS"
    • While waiting received the error, "macOS Sierra failed to download. Use the Purchases page to try again"
    • Exited Reinstall and started new Reinstall attempt
    • Progress bar did not move after several minutes. No error message this time.
    • Rebooted iMac and went back to OS X Recovery
    • Selected "Disk Utility"
    • Selected "Macintosh HD" and selected "Erase" with "Macintosh OS Extended (Journaled)" as the option.
    • Macintosh HD erased and Disk Utility stated "Operation Successful"
    • Selected "Reinstall MacOS"
    • Reinstall completed successfully and rebooted
    • Created new TEST account
    • Logged into the TEST account
    • I did not experience the issue immediately, so Apple Support asked that I monitor the iMac for 24 hours before restoring any backups
    • Used the computer in the new TEST account for about 1 hour
    • Experienced the issue
    • Contacted Apple Support again
    • Had me perform Apple Diagnostics via holding down D key while rebooting
    • Asked me to do "Extended Test" if available as an option
    • Computer did not present any options and just began running the diagnostic test
    • After about 5 minutes it came back with the following result, "No issues found. Reference Code: ADP000"
    • Next, had me restart into OS X Recovery mode via Command-R
    • Selected "Disk Utility"
    • Selected "Macintosh HD"
    • Apple Support had me take a picture of the screen and send it to them (included in Dropbox link below)
    • They set up an appointment at the local Apple Store for this past Wednesday
    Apple Store:

    • Dropped off the computer at the Apple Store, explained all the issues I was experiencing.
    • While I was there, they ran a 5 minute diagnostic on the iMac and no problems were found
    • Below is the Problem Description/Diagnosis captured by the Apple Store when I dropped it off.

    Problem Description/Diagnosis

    Issue: Customer states that machine will freeze and he won't be able to do anything. He says when it freezes it just will not respond to the clicks when clicking on anything. We don't get a colored spinning wheel he states when that happens.

    Steps to Reproduce: Ran Mac Resource Inspector and found no issues.
    I booted to his test user account that was created after a reinstall that was performed with phone support, could not replicate issues.
    Cosmetic Condition: No damage to display or enclosure.
    Proposed Resolution: Check in for full ASD testing.
    Estimated Turn Around Time: We'll call you within 48 hours
    Mac OS Version: Unknown
    Hard Drive Size: 3000
    Memory Size: 32768
    iLife Version: Unknown

    • They kept the iMac to do their testing
    • I received a call on Friday from the Apple Store and they stated that the 24 hour diagnostic did not find any problems. I explained I was surprised by this due to the frequency of the issue. The Apple Store stated the freezing was probably caused by my Internet connection. Note we have four other MacOS computers in our house, including an older iMac and none of them experience this same issue.
    • They stated they would do a "deep" reinstall that only they can do. This was to make sure everything possible is removed and it is restored to the original state.
    • I picked up the computer and brought it back home and booted it up last night
    • The computer had macOS Sierra installed, but did not have an account set up
    • Created new TEST account
    • Logged into the TEST account
    • Used computer for ~10 minutes
    • Experienced the issue
    • I continued to use the computer and experienced the issue multiple times
    Additional Troubleshooting Performed Based On My Own Research:
    Below is all the troubleshooting steps I completed after bringing the iMac home from the Apple Store. The steps below are cumulative in that each change I made remained in place for the subsequent steps, so with each step more variables have been removed from the environment to hopefully narrow the possible causes of the issue. In all of the cases below, the only software installed on the iMac is what comes standard with the OS, except where noted.

    Based on my experiments last night I developed a test that has been successful in causing the freezing issue to occur, documented below. This is the test I ran after each troubleshooting change documented below.

    The Test
    • Open Safari browser window
    • Note Safari is the only application running during this test
    • Go to
    • Play a music video, I used "Coldplay - The Scientist" in each test, so it was consistent from test to test. Also, it was first video I ran across that I could stand listening to over and over.
    • While the music video is playing, open a separate browser window in Safari
    • Go to
    • Click on "Videos"
    • Begin slowly scrolling down the page, pause until the first video begins playing
    • Let the video play for a few seconds and then scroll down to the next video until it starts playing
    • Repeat this process for each video letting each one play a few seconds until the iMac freezes
    • In most cases the iMac freezes before the Coldplay - The Scientist video finishes which is 4:26 long. Occasionally it will start the next Coldplay song, but this is rare, and I almost always experienced the freezing before the second song completed.

    Clean Reinstall: Yosemite 10.10.5
    • Since I continued to experience the issue after picking up the computer from the Apple Store, I decided to do another reinstall. First I did an SMC Reset and NVRAM/PRAM reset. I booted into OS X Recovery and erased the hard drive, then reinstalled the OS. Yosemite was the only OS option available, I assume Yosemite was the only option due to the "deep" reinstall performed at the Apple Store.
    • After Yosemite was installed, I created a TEST account and checked for any software updates. There were several updates which I installed. Since I hadn't run Yosemite for a while, I took the opportunity to see if I would experience the freezing under this older OS. Note, I did not install any other software at this point. The only software installed is what is standard with Mac OS.
    • With Yosemite installed and fully updated, I performed "The Test"
    • Experienced the issue

    Clean Reinstall: macOS Sierra 12.0
    • With the confirmation the issue occurred in Yosemite I downloaded macOS Sierra from the App Store and installed it
    • Just to be extra cautious and to insure the issue was not caused by some legacy Yosemite software installs, I then rebooted into OS X Recovery, erased the hard drive and did a clean install of MacOS Sierra
    • With macOS Sierra installed I ran "The Test"
    • Experienced the issue

    Disconnect Third-Party Peripherals
    • To confirm that the issue wasn’t caused by third-party peripherals plugged into the iMac, I unplugged the following peripherals:
      • Fujitsu ScanSnap S1500M directly connected via USB cable to back of iMac
      • Demo LabelWriter Duo directly connected via USB cable to back of iMac
      • Klipsch external speakers directly connected via audio cable into headphone port on back of iMac
    • The following peripherals remain connected to the iMac:
      • Apple USB extended keyboard
      • Amazon Basics USB mouse with two buttons and scroll wheel
    • After unplugging the above peripherals, I rebooted the computer and I ran "The Test"
    • Experienced the issue

    Disconnect Apple AirPort Extreme AC with External Time Machine Back Up Disk & Disable WIFI:
    • Early on I had developed my own theory that Time Machine backups and the periodic disk access might be causing the iMac to freeze. This was not based on anything I found in my research, just a hunch. My Time Machine back up disk is connected to an AirPort Extreme AC and my iMac is plugged into the Airport directly via ethernet cable.
    • Now, after all the reinstalls I had not turned on Time Machine, but just in case the disk access by other Macs on our network was causing the freezing issue on the iMac, I bypassed the Airport entirely and plugged the iMac ethernet cable directly into my cable provider's router. I also disabled WIFI on the iMac in case that was causing any issues.
    • For the record my provider is AT&T UVerse and Ariss AVG589 is my modem
    • After eliminating the AirPort Extreme and Time Machine disk from the picture, I ran "The Test"
    • Experienced the issue

    Disable Bluetooth in System Preferences
    • I read that some eliminated the issue by disabling Bluetooth. I disabled this in System Preferences, closed Safari, restarted the computer and ran "The Test"
    • Experienced the issue

    Disable "Allow WebGL" in Safari Preferences
    • I read that disabling “Allow WebGL” in Safari fixed this issue for some people. I disabled this setting, closed Safari, restarted the computer and ran "The Test"
    • Experienced the issue
    • I will say the iMac ran a little bit longer under this condition, but maybe I just got lucky

    Install Chrome with “Use Hardware Acceleration when available” Disabled
    • There were many suggestions on using alternate browsers with Chrome being the one most mentioned. In some posts they suggested turning off “Use Hardware Acceleration when available”
    • I installed Chrome, turned off this setting, restarted the computer and ran "The Test"
    • Experienced the issue
    • While it took a little longer for the iMac to freeze with Chrome as the browser, maybe three Coldplay songs vs the usual one it did eventually occur

    Other Notes And Observations:
    • As mentioned earlier in the post, the screen image does display strange artifacts during some of the freeze ups. Screenshot attached and another one in the dropbox folder linked below.
    • After one of the freezes and restarts I captured logs from the console app. There were 16 entries titled with the following naming schema, “Kernel_YYYY_MM_DD_TTTTTTTT_TESTs-iMac.gpuRestart”. These logs are also in the linked Dropbox folder. These occurred during the same restart that I captured the screenshots from.
    • As I browsed the logs, there multiple mentions of a “GPU Restart” immediately prior to the crash and restart. I tried to capture as many of the logs that looked to be relevant to this issue and included them in the Dropbox folder.
    • After one restart I received a pop up from the system wanting to send information to Apple regarding a, “Sleep Wake Failure”. I captured the details and included in the Dropbox folder.
    • Below is a run from EtreCheck since that seemed to be a common request in other posts.

    Dropbox link with log files and screenshots:

    EtreCheck Results:

    EtreCheck version: 3.0.6 (315)
    Report generated 2016-10-15 12:19:08
    Download EtreCheck from
    Runtime 1:18
    Performance: Excellent

    Click the [Support] links for help with non-Apple products.
    Click the [Details] links for more information about that line.

    Problem: Computer is restarting

    Hardware Information:

    iMac (Retina 5K, 27-inch, Late 2014)
    [Technical Specifications] - [User Guide] - [Warranty & Service]

    iMac - model: iMac15,1

    1 4 GHz Intel Core i7 CPU: 4-core

    32 GB RAM Upgradeable - [Instructions]

    BANK 0/DIMM0

    8 GB DDR3 1600 MHz ok

    BANK 1/DIMM0

    8 GB DDR3 1600 MHz ok

    BANK 0/DIMM1

    8 GB DDR3 1600 MHz ok

    BANK 1/DIMM1

    8 GB DDR3 1600 MHz ok

    Bluetooth: Good - Handoff/Airdrop2 supported

    Wireless: en1: 802.11 a/b/g/n/ac

    Video Information:

    AMD Radeon R9 M295X - VRAM: 4096 MB

    iMac 5120 x 2880

    System Software:

    macOS Sierra 10.12 (16A323) - Time since boot: less than an hour

    Disk Information:

    APPLE SSD SM0128G disk0 : (121.33 GB) (Solid State - TRIM: Yes)

    EFI (disk0s1) <not mounted> : 210 MB

    Boot OS X (disk0s3) <not mounted> : 134 MB

    Macintosh HD (disk2) / [Startup]: 3.11 TB (3.10 TB free)

    Core Storage: disk0s2 120.99 GB Online

    Core Storage: disk1s2 3.00 TB Online

    APPLE HDD ST3000DM001 disk1 : (3 TB) (Rotational)

    EFI (disk1s1) <not mounted> : 210 MB

    Recovery HD (disk1s3) <not mounted> [Recovery]: 650 MB

    Macintosh HD (disk2) / [Startup]: 3.11 TB (3.10 TB free)

    Core Storage: disk0s2 120.99 GB Online

    Core Storage: disk1s2 3.00 TB Online

    USB Information:

    Apple Inc. BRCM20702 Hub

    Apple Inc. Bluetooth USB Host Controller

    Apple Inc. FaceTime HD Camera (Built-in)

    Apple, Inc. Keyboard Hub

    Apple Inc. Apple Keyboard

    Thunderbolt Information:

    Apple Inc. thunderbolt_bus


    Mac App Store and identified developers

    System Launch Agents:

    [not loaded] 5 Apple tasks

    [loaded] 182 Apple tasks

    [running] 84 Apple tasks

    System Launch Daemons:

    [not loaded] 42 Apple tasks

    [loaded] 166 Apple tasks

    [running] 94 Apple tasks

    User Login Items:

    iTunesHelper Application (/Applications/

    Internet Plug-ins:

    QuickTime Plugin: 7.7.3 (2016-09-13)

    3rd Party Preference Panes:


    Time Machine:

    Time Machine not configured!

    Top Processes by CPU:

    21% assistant_service

    3% WindowServer

    3% fontd

    0% assistantd

    0% kernel_task

    Top Processes by Memory:

    1.35 GB kernel_task

    98 MB Dock

    66 MB softwareupdated

    66 MB mds_stores

    66 MB Finder

    Virtual Memory Information:

    28.00 GB Free RAM

    3.81 GB Used RAM (1.31 GB Cached)

    0 B Swap Used

    Diagnostics Information:

    Oct 15, 2016, 12:05:11 PM Self test - passed
  2. tomantrim thread starter macrumors newbie

    Oct 15, 2016
    Spent some time talking to an Apple tier 2 advisor this week. He provided a capture program to grab logs and I uploaded them to Apple. A tier 3 advisor (think that is what he called them) will look at the logs to determine if there are any hardware issues.

    Since there were no responses. I'm taking down the dropbox link.

  3. BrianBaughn macrumors 603


    Feb 13, 2011
    Baltimore, Maryland
    Be sure to let us know what happens. My guess is that you'll get the Mac replaced and won't find out exactly what's wrong with it.
  4. Chiily macrumors newbie

    Jul 28, 2016
    I know this might sound like the most unlikely thing ever, but have you tried plugging it in to a different power socket in a different room with a different extension....

    Any large power consumers in your house or around your house?

    It just smacks of something specific to your house, power quality....
  5. Fishrrman macrumors P6


    Feb 20, 2009
    OP -

    Just wondering -- is the RAM original, or have you changed/added any?
  6. JorgeZ macrumors newbie

    Oct 24, 2016
    Curious to the eventual solution. I purchased the same model in July and it started to freeze and reboot in September, a few times a day. Support was not helpful. They only suggested wiping hard drive and doing clean install.

    I have searched other forums and this problem has been an issue for a few years now. Most required a new logic board and/or power supply.

    I'm still taken aback that after pending almost 3K on a new computer, Apple is so dismissive. They keep insisting I reinstall OS. Not sure if I trust leaving it at the store for a week.

    Good luck!
  7. rafiksamman macrumors newbie


    Sep 7, 2017
  8. rafiksamman macrumors newbie


    Sep 7, 2017
    Just wondering !!! did you at any point add more ram dimms on your mac. I was experiencing the same problem. It started when I replaced 2 original 4GB RAM DIMMS with 8GB from OWC.

    I removed the 8GB DIMMs and now everything is back to normal. No more freezing or crashing.

    --- Post Merged, Sep 7, 2017 ---
    Just wondering !!! did you at any point add more ram dimms on your mac. I was experiencing the same problem. It started when I replaced 2 original 4GB RAM DIMMS with 8GB from OWC.

    I removed the 8GB DIMMs and now everything is back to normal. No more freezing or crashing.

  9. kohlson macrumors 68000

    Apr 23, 2010
    You've spent too much time on this -- unfortunate. As suggested above, could be memory if not Apple memory. It looks like you can reproduce the problem without much effort. Perhaps a cellphone video set up of the symptoms, such that this can accompany your case file?

    Another question: Can you boot to a clean OS and does that work better? Could be from an external disk.
  10. erininLA macrumors newbie

    Jun 7, 2018
    HI Friend, curious, did you replace with Mac memory or 3rd party? thank you!
  11. hobowankenobi macrumors 6502a

    Aug 27, 2015
    on the land line mr. smith.
    Nevermind...missed the age of this thread.

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10 October 15, 2016