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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Desktops > 27” iMac odd behavior

27” iMac odd behavior
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sek929
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Mar 26, 2018, 07:07 PM
 
In sort of a carry over post from this thread I now believe that the HDD is dying in my iMac. What first manifested as strange partition errors is now rendering the machine near useless.

Booting into Sierra either hangs at the Apple, or manages to load and eventually crash. Booting into Win10 eventually loads but threw a “reboot to repair drive errors” before it, too, got hung up.

I have a very recent Time Machine backup but I don’t think I should even bother trying to reinstall, right?

This kinda blows but offers me a good excuse to upgrade to an SSD

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reader50
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Mar 26, 2018, 09:38 PM
 
Did you follow the advice in the other thread, and completely erase/repartition/reinstall both OS's? If you haven't wiped away the Bootcamp stuff and recreated from scratch, then you're still in the hole with nonstandard partition maps. You should also reset the SMC after fooling around with the boot drive.

btw, what year/config is the iMac? What is the existing HD size?
     
sek929  (op)
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Mar 27, 2018, 07:27 AM
 
I wiped the whole computer and installed Sierra and Win 10 from scratch on a new partition. Yesterday while trying to get it to boot properly resetting the SMC was something I tried with no luck.

It’s a late 2011 i7 w/1TB HDD

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reader50
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Mar 27, 2018, 02:26 PM
 
It's plausible the HD is getting old.

It might be worth a PRAM reset first. My Mac seems to track the boot partition layout, probably to accelerate bootup, and gets confused if I adjust partitions. It can take a few resets before the "magic" kicks in, and things sync again. Then it boots perfectly, like nothing had happened.
     
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Mar 27, 2018, 05:53 PM
 
HDD is a likely option. RAM is somewhat unlikely but way easier to troubleshoot since it can easily be removed, so you may want to try that first (remove all sticks but one, see if the error remains). Can be something strange like a borderline PSU failure that craps out when overheating, but that is always hard to analyze.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
sek929  (op)
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Mar 27, 2018, 07:03 PM
 
I should also add something I forgot about. Last week the desktop picture started flashing black, at first it looked like the screen was malfunctioning but the Finder bar at the top stayed on the screen fine, it was just the desktop picture. The machine sputtered a bit and eventually I hit the power button to shut it down. Cursory googling showed the black screen problem was fairly common issue, but no real solutions that I saw.

I’ve also zapped PRAM and started in safe mode, both didn’t work.

I’ll pull some sticks of RAM and see what happens.

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reader50
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Mar 27, 2018, 08:42 PM
 
Oh dear, GPU problem. That would explain all the other instability. You can (and should) take your iMac apart to clean the heatsinks/fans/air passageways. If you're really lucky, that will cure it. If you're lucky, it will be the heat pipe has leaked the refrigerant and needs replacement. If unlucky, the GPU is damaged.

Assuming it is the GPU (and the HD may be fine today), the cheapest solution would be an MXM PC vid card. You'd lose bootup video, which is a drag for troubleshooting. Mac MXM cards are less common, and pricey. You could try an eGPU enclosure with a real video card, but Apple is playing games with the 10.13.4 betas. Blocking eGPUs over Thunderbolt 1 or 2 (you have TB1). The block may vanish or be easily turned off once 10.13.4 final is released.
     
sek929  (op)
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Mar 28, 2018, 04:15 PM
 
If it was the GPU then why did the menu bar and dock stay on the screen while the desktop picture flashed? Not being disagreeable but scrolling through the Apple support forums on this topic yielded that this was most likely a software issue and not a particular hardware fault.

Wife just informed me that she used the computer all day without issue, it’s still running now

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sek929  (op)
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Mar 28, 2018, 05:29 PM
 
So now that I can sit at an actual computer and do some more research properly (iOS frustrates me) I have found the following.

Mid to Late 2011 27" iMacs with the same 3.4 i7 as mine do have a known fault with the GFX card, but it's the ATi card, mine is an Nvidia. I'm still not ruling out the video card because I have a second, dead, i3 from 2013 with a fried card on my desk.

Anyone got a ballpark what Apple would charge me to replace such a thing? I got this computer for free so I wouldn't mind liiiike, 400 tops?

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Mar 28, 2018, 06:31 PM
 
Apple won't supply parts if the machine was last sold more than 5 years ago, unless you are in CA. They'll go 7 years here, due to product support laws.

The menubar is a good point, though it's likely in a different layer. The inconsistency of the problem could indicate two problems, like a glitch in a VRAM chip + a weak power supply. Or something else.

Did the wife use it in a different location, plugged into a different socket? Is her usage pattern different, such as no games or anything else that stresses the GPU? Or with a different peripheral plugged in? If it were mine, I'd want to diagnose further, until a clear pattern emerges. If you bought new parts at this stage, there's a good chance it would fail to address the problem(s).
     
sek929  (op)
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Mar 28, 2018, 09:18 PM
 
She's a much lighter user but was the first one to experience the "flashing black" screen.

Randomly today she hit the power button and it worked. I've gamed pretty heavy in Win 10 and more recently Minecraft under OSX. After my latest crash the computer sat off for ~24 hours before I had my issues booting into both OSes. Same outlet, same peripherals. Right now running like a champ, I'll run Minecraft for a bit, let the machine warm up, and see what happens.

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Mar 29, 2018, 07:10 AM
 
GPU is a possibility, but the screen background can flash if something crashes. Have you run the hardware tester?

https://support.apple.com/en-us/HT201257

Is the machine physically hot on the back anywhere when this happens?
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
sek929  (op)
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Mar 29, 2018, 10:33 AM
 
Even when the fans ramp up during gaming sessions in Win10 the aluminum back is barely warm, my old 2007 iMac used to get a hell of a lot hotter when gaming.

I played Minecraft for a few hours last night with no issue. Fans ramped up and everything but it still ran silky smooth.

I’ll run the diagnostics when I get home today and report back.

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sek929  (op)
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Mar 30, 2018, 12:05 PM
 
Computer locked up after a rather short Minecraft session, preceded by some whirring and clicking noises from the HDD. Didn’t have a chance to run the diagnostic yet but I’m leaning pretty heavily toward a failing HDD

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Mar 31, 2018, 04:35 AM
 
Yes, if the HDD is making noises, that is bad.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
sek929  (op)
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Mar 31, 2018, 11:49 AM
 
On boot up I get the little click/whir sound usually before the boot either takes ages or hangs up. Also, some times during boot the screen goes black at the Apple logo and needs to be shut down manually.

Ran the extended diagnostics, 1 hour and 45 minutes worth "no issues detected" harumph. Booting back to OSX afterwards I got this screen.



Once again the screen was fine and smooth but those random assets were garbled on screen. An SMC reset later the machine is running fine now...

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Apr 3, 2018, 04:55 AM
 
I think that the drive is bad. You could try grabbing the full SMART data set using smartmontools and post here and I will try to read it, but I think that the drive is likely shot.

https://www.smartmontools.org/wiki/D...XDarwinpackage

If the hardware test passes, it is unlikely that the issue is the CPU, GPU or RAM. It can still be PSU (which cannot be tested), it can be cooling, and it can be the HDD (as hard drive manufacturers set too lenient pass criteria for their drives, to cut down on warranty costs).
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
sek929  (op)
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Apr 13, 2018, 09:56 AM
 
Was away at PAX last weekend and quite busy this week but the computer fails to boot entirely now. Gave me the “?” Folder icon yesterday.

There’s a certified Mac shop near me, 75 bucks for a diagnostic. I was planning on bringing it to them for the final verdict, though if they say HDD is failing I’ll probably do the fix myself. Should I forgo the diagnostic all together and just swap the HDD out anyways?

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reader50
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Apr 13, 2018, 11:59 AM
 
Pick up a USB external, install the OS, and see if it settles down. You should have an external anyway - makes diagnostics far easier.

If you're going to spend ~$75, you might as well end up with something you can keep.
     
sek929  (op)
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Apr 13, 2018, 12:48 PM
 
I have an external drive with time machine backups galore, could I just boot off of those?

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Apr 13, 2018, 02:01 PM
 
No, TM backups are not bootable. You could partition and install on a 2nd partition, but it is wiser to leave your backups alone. Especially when your primary HD is in doubt.

I wouldn't do *anything* with that backup right now. It's the only copy you know is intact. Put it in the safe, and get a cheap external for testing.
     
sek929  (op)
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Apr 13, 2018, 04:23 PM
 
Okay another noob question, can I make a USB drive bootable, I have several 32GB sticks

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Apr 13, 2018, 04:32 PM
 
They'll boot. I haven't tried installing to one lately, only cloning to one. So I don't know offhand if the Installer will accept them. But they definitely work once you get macOS onto one.
     
sek929  (op)
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Apr 13, 2018, 04:58 PM
 
Alright then, I’ll give a it go tonight and see if I can get some stability while running on the thumb drive.

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sek929  (op)
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Apr 14, 2018, 12:09 PM
 
I was able to boot in recovery mode and install mountain lion on to a USB stick but I never was able to boot from it, it didn’t show up in the menu at startup. In fact, now booting into recovery mode and using disk utility the HDD isn’t showing up at all anymore.

It sat in recovery mode for hours as I made dinner and other things, never shut off or acted strange, im going to assume the machine is fine and the HDD is dead and go from there.

Going to start looking at SSDs and the assorted tools I need to crack this thing open my wife is losing patience with not having a working computer.

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sek929  (op)
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Apr 14, 2018, 12:50 PM
 
Leaning toward OWC’s SSD upgrade kit. Comes with adapter bracket and alll the tools you need, plus an in-line thermal sensor, which I have read could cause the fans to get confused after a swap out of the OEM drive.

https://eshop.macsales.com/item/OWC/K27IM12HE500/

Going to give the USB stick route one more go today, but I have to get this project going.

Edit: after an SMC reset the Mac and Win partitions showed up again in the startup list, I’m getting a headache...

Edit2: For shits I booted up in verbose mode, machine never actually started up but it was throwing a lot of disk0s2 I/O errors, which I remember from my last failing HDD. I’m going to pull the trigger on the SSD kit from OWC and hopefully have this machine back on it’s feet next weekend.
( Last edited by sek929; Apr 14, 2018 at 02:39 PM. )

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Apr 16, 2018, 04:47 AM
 
Edit2: For shits I booted up in verbose mode, machine never actually started up but it was throwing a lot of disk0s2 I/O errors, which I remember from my last failing HDD. I’m going to pull the trigger on the SSD kit from OWC and hopefully have this machine back on it’s feet next weekend.
This means that a failing drive is highly likely, but it CAN be the cable or the SATA controller as well. If it is the SATA controller - well, nothing much to do, it's in the PCH on that model. Apple had issues with failing SATA-cables on the MBP, but I haven't heard of it being a problem on an iMac.

If your new SSD does not work still, try installing it in the optical bay. If the issue is the cable that should fix it (assuming there is nothing connected to the HDD SATA cable).
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Apr 16, 2018, 05:18 AM
 
I agree with P -- i/o errors almost always mean drive problems.

btw, did you retry booting from your flash drives after doing that SMC reset? If a bad drive had crashed the SMC, that would explain a failure to boot from anything.
     
sek929  (op)
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Apr 16, 2018, 09:28 AM
 
The problem is, I think, that after formatting the thumb drive you need to change the permissions via the Finder, something about unchecking a box allowing the installer to create secure files or something. Since I can’t get the machine to boot I was never able to change said permissions.

I have considered that a bad controller or something else may be the root cause, but I’m going with my gut that a new SSD will solve all my problems. The fact that initially wiping the machine and trying to partition it threw up some strange boot sector issues all but confirms it’s probably a bad drive, if it’s the controller and therefore the main board then I guess I’ll use the SSD elsewhere...

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Apr 16, 2018, 01:13 PM
 
Even if the controller is blown on both channels, you can switch to externals. Put the new SSD in an enclosure, and you'd still get most of the speed benefits.
     
sek929  (op)
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Apr 21, 2018, 02:44 PM
 
Hellz to the yeah!

Cracking it open was easy, swapping the drives was easy, setting the new tape strips was moderate and aligning the display and sticking it down was definitely the hardest part.

Thanks to the Time Machine backup I was able to boot the machine into recovery mode, format the SSD and restore my computer to its former glory in under 30 minutes.

Theres so much extra room inside the 27" chassis it makes me wonder why the bloody thing has to be so thin, and had to have its screen glued on.

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Apr 23, 2018, 05:17 AM
 
I have always felt that the 2012 redesign of the iMac was a mistake. The 27" didn't do so poorly, but the 21.5" is certainly worse than its predecessor. Somewhere in that era, Apple clearly decided that its computers should be hard to open and unupgradeable to entice people to stay out of modifying them, and I think it was a mistake.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
sek929  (op)
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Apr 23, 2018, 12:49 PM
 
In the newer machines even the RAM is not user upgradable anymore right? That is a massive **** you to customers.

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sek929  (op)
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Apr 23, 2018, 05:27 PM
 
Side Note: This machine flys now, hot damn SSD, you've done it again.

Basically, I can never buy a computer going forward that doesn't have a SSD as the boot drive. Is Apple's fusion drive worth the cost?

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Apr 25, 2018, 03:51 AM
 
Originally Posted by sek929 View Post
In the newer machines even the RAM is not user upgradable anymore right? That is a massive **** you to customers.
It varies a bit, but right now you can upgrade the RAM in all iMacs and the MP, and not in any other model. It is however really finicky to get to in some iMacs, but Apple will do it for you.

All the laptops use LPDDR RAM now, and that doesn't exist as DIMMs, so it has to be soldered.

Originally Posted by sek929 View Post
Side Note: This machine flys now, hot damn SSD, you've done it again.

Basically, I can never buy a computer going forward that doesn't have a SSD as the boot drive. Is Apple's fusion drive worth the cost?
Fusion drives make some sense in that you can have MASSIVE storage and get decent speed, but I think that their time has passed. A 500 GB SSD can be had by the consumer for roughly what a middling HDD used to cost - it is a little high right now because of speculators in the NAND market - and that should be enough for the vast majority of users. Long term, I think Apple will make future Macs without space for internal spinning storage and let people use external storage if they need it. USB 3.0 with UASP is fast enough for any spinning disk.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
   
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