2011 imac random restarts

[5chulzy]

Hi I was given a 2011 27 imac that was having a few problems and after doing a bit of research I found out about the dreaded gpu issues. I decided to try and repair myself by putting the gpu in the oven and was pleasantly surprised to find that it now worked.

I used some k4 and k5 thermal paste when replacing the graphics card and also done the cpu at the same time.
I've increase the 4gb ram to 12gb and swapped out the ODD for a 250gb ssd.

Now everything seems to be running prefect, I have connected 2 x 23 inch dell monitor's using the thunderbolt connections to displayport on the monitors. Some times I can stream a 4k video on YouTube, a film on Netflix and a 4k movie on an iptv app on all 3 screens and have no problems. But occasionally the mac will crash and screens will go blank and you can hear a sound going on loop for a split second like it's bleeping really fast. After about 30 second the mac will then restart.

I've search in terminal for shutdown causes and it comes back with -128

I turned the brightness down on the mac screen and it seems to of helped, shutdowns are less frequent. But is there a permanent fix or is this something I will just have to put up with. I've also reset pram and smd. Erased original 1tb HDD and have osx running on the sdd

 

[mdgm]

Baking the GPU is just a temporary fix. You could try undervolting the GPU as well. I've read that that can help. Replacing the GPU with one of the AMD GPUs from 2011 iMac Graphics Card Upgrade is probably the longer term solution. The Nvidia ones could be considered as well but aren't the best choice for running the latest Mac OS though unsupported as Nvidia support has been dropped from Monterey.

The optical drive SATA connector is limited to SATA II whereas the hdd connector and the spare connector are SATA III. Replacing the hdd with a SSD will make the machine run cooler (less heat is better for the GPU) though if you want the inbuilt fan control to work with the stock GPU you'd need a thermal sensor cable.

 

[Nguyen Duc Hieu]

Hi I was given a 2011 27 imac that was having a few problems and after doing a bit of research I found out about the dreaded gpu issues. I decided to try and repair myself by putting the gpu in the oven and was pleasantly surprised to find that it now worked.

I used some k4 and k5 thermal paste when replacing the graphics card and also done the cpu at the same time.
I've increase the 4gb ram to 12gb and swapped out the ODD for a 250gb ssd.

Now everything seems to be running prefect, I have connected 2 x 23 inch dell monitor's using the thunderbolt connections to displayport on the monitors. Some times I can stream a 4k video on YouTube, a film on Netflix and a 4k movie on an iptv app on all 3 screens and have no problems. But occasionally the mac will crash and screens will go blank and you can hear a sound going on loop for a split second like it's bleeping really fast. After about 30 second the mac will then restart.

I've search in terminal for shutdown causes and it comes back with -128

I turned the brightness down on the mac screen and it seems to of helped, shutdowns are less frequent. But is there a permanent fix or is this something I will just have to put up with. I've also reset pram and smd. Erased original 1tb HDD and have osx running on the sdd

You can try underclock the GPU, and reduce the load (2,3 monitors, 4K videos streaming etc.). You have overstressed a handicapped GPU.
Or you can retire the GPU and use a metal support GPU.