How to determine if the graphics card is at fault on an iMac?

Question

I ended up with an Mid 2010 21.5" iMac that I wanted to dust off and give to my kids. They have light needs, but I'd love to start introducing them to messaging and email with family, plus some educational games.

I can't remember all the problems I've had, but over the last few years I replaced the HDD with an SSD and a few days ago I boosted the RAM from 8GB to the max of 16GB. I reset the PRAM/NVRAM and I thought all my problems were fixed. Then today I logged in to pat myself on the back for getting this up and running again and it was exhibiting the same behavior I was trying to solve.

Specifically, it's been logging me out a handful of times before it "sticks" and lets me use the computer. When booting up, the login screen often looks pixelated, and I can see a black/gray grid in certain spots behind the login screen. It also looks like someone has taken a knife across the screen, showing long lines of distortion fragments. I log in, then bam, get logged out shortly after.

Some things I've tried:

• As mentioned, replaced HDD with SSD and maxed RAM to 16GB
• Completely wiped the SSD and reinstalled High Sierra (the max this machine can take. these issues have occurred through at least the last few major OS updates
• Apple Hardware test won't run (probably because I wiped my drive) and Internet Recovery fails too
• Run memory checks
• Repaired Disk Permissions

I found this thread on reddit about finding crash logs, and when I looked, I found many instances of these two types of crashes:

Kernel_2019-01-25-122634_Boys-iMac.gpuRestart
Kernel_2019-01-25-122650_Boys-iMac.gpuRestart
Kernel_2019-01-25-122700_Boys-iMac.gpuRestart
Kernel_2019-01-25-122749_Boys-iMac.gpuRestart

and

WindowServer_2019-01-25-122534_Boys-iMac.crash
WindowServer_2019-01-25-122626_Boys-iMac.crash
WindowServer_2019-01-25-122659_Boys-iMac.crash

Looking at the timestamps, they seem to line up with this afternoon's frustrating experience, crashing about every 20 seconds (log in, auto log out, log back in, repeat).

I don't totally know how to read these reports, but here's an example of some of the outputting the Kernel.gpuRestart crash:

Fri Jan 25 10:26:27 2019

Event:               GPU Reset
Date/Time:           Fri Jan 25 10:26:27 2019
Application:         WindowServer
Path:                
Tailspin:            /Library/Logs/DiagnosticReports/gpuRestart2019-01-25-102627.tailspin
GPUSubmission Trace ID: 0
OS Version:          Mac OS X Version 10.13.5 (Build 17F77)
Graphics Hardware:   ATI Radeon HD 5670
Signature:           0

Report Data:

GPURestartReportStart
------------------------
Hung Channels: PM4 
------------------------
[00] AccelChannel: PM4
Pending Command from   : GLCtx
PendingCommandTimestamp: 0x00000de3, TotalDWords: 0x0000025f, GART Offset=0x0000000020b3a780, stamp_idx=0, estamp=0x00000de3
------------------------
[00] PM4 HWChannel  : Enabled, NotIdle
LastReadTimestamp   : 0x00000de2
NextSubmitTimestamp : 0x00000e26
[PM4, ts:0x00000de3]: No semaphore wait
[PM4, ts:0x00000de3]: semaphore  signal: 0xffffff8033e8c9c0
HWSemaphore 0xffffff8033e8c9c0 Signal Event: [PM4 channel[0] TS:0x00000de3 lastReadTS:0x00000de2]
------------------------
GPU HangFlags 0x00000006: AsicHangState 0x00000006, AsicResetRequirement 0x00000002
IndividualEngineHang: 0
NonEngineBlockHang  : 1
FenceNotRetired     : 1
PerEngineReset      : 0
FullAsicReset       : 1
HangEngineBitmap    : 0x00000000
------------------------
AMDRedwoodGraphicsAccelerator PCIe Device: [1:0:0] State: ENABLED
Configuration: deviceBits: 0x002068c0, capabilityBits: 0x30940100
TotalVideoRAMBytes: 0x0000000020000000 (536870912)

And here's an example from the output of the WindowsServer.crash:

Process:               WindowServer [425]
Path:                  /System/Library/PrivateFrameworks/SkyLight.framework/Versions/A/Resources/WindowServer
Identifier:            WindowServer
Version:               600.00 (312.62)
Code Type:             X86-64 (Native)
Parent Process:        launchd [1]
Responsible:           WindowServer [425]
User ID:               88

Date/Time:             2019-01-25 12:26:58.581 -0800
OS Version:            Mac OS X 10.13.5 (17F77)
Report Version:        12
Anonymous UUID:        C1090F37-DA86-08E5-7F8C-BF0AAE4C2C91


Time Awake Since Boot: 110 seconds

System Integrity Protection: enabled

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_CRASH (SIGABRT)
Exception Codes:       0x0000000000000000, 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

Application Specific Information:
StartTime:2019-01-25 12:26:25
GPU:
MetalDevice for accelerator(0x4b0f): 0x7fcf1570f468 (MTLDevice: 0x0)
IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/P0P2@1/IOPP/GFX0@0/ATY,Galago@0/ATY_Galago
abort() called

Application Specific Signatures:
Graphics hardware encountered an error and was reset: 0x00000000

I feel like it's obvious that the gpu is at fault here, but I'm a little over my head and thought I'd ask the more experienced and enlightened.

1. Do you think it's likely (how likely?) that replacing the gpu will solve these problems?
2. If very likely, I figured out how to find the graphics card I need, but I'm wondering if there cheaper alternatives. I don't need anything heavy duty. This won't be a gaming PC. Just messaging, FaceTime, and a platform for my kids to explore.

Thanks so much for all your help!

Answer 1

You should try safe mode. Safe boot: Shutdown your machine. Hold down the shift key. Poweron. The boot up will take longer than normal because the filesystem on the startup drive is being checked and repaired as needed. All about safe mode including what features and apps safe boot leaves out. Safe boot uses a software driver instead of using your machines video hardware. http://support.apple.com/kb/ht1455

If the machine works in safe mode, you can set up your machine to run the safe mode video drivers in normal mode.
Runs OK in safe mode... Running in Safe mode leaves out some video drivers. Which results in your machine not using advanced video hardware. As luck would have it, you can run the safe mode video drivers in normal mode.

Here is how: https://discussions.apple.com/message/16057567#16057567

Look through the above thread. See the second page. You don't have to read through the first page. Just go to the part where I try a solution that works.

On Sierra and beyond, you need to turn off SIP, System Integrity Protection before making the changes. You should turn SIP back on after you're done making the changes. SIP prevents alteration to system files.

https://www.macworld.co.uk/how-to/mac/how-turn-off-mac-os-x-system-integrity-protection-rootless-3638975/

Using the safe mode video driver disables accelerated graphics.

Answer 2

Multiple GPU restarts and resets on 2009 and 2010 era Macs is almost certainly GPU failures. If you wanted to get two or three scrap Macs and teach your users repair / see if they can learn how to scavenge parts - that would be a wonderful education for low cost.

Here is an amazing (to me) story of a DIY reflow of the GPU to salvage the existing hardware if the GPU has simply lost electrical connection with the hundreds of pins that connect it to the system.

• https://apple.stackexchange.com/a/257567/168832

If you want a stable computing experience, I would get a $20-30 raspberry pi or even an Arduino and work up from the low end with them.

There always will be some fraction of Macs that run forever, but the longevity of these early model Intel Macs isn’t as long as the PPC predecessors. I’d go for a modern computer and iOS device for games / messaging to get much more bang for your buck and less time maintaining the hardware.