Color dots appear in bands across the screen, especially after switching displays, and then eventually the system freezes. Anyone seen this. iMac 27" late 2011.
iMac 27", macOS 10.13
What ever speeds are needed to keep the GPU at least as cool as possible, on my 2001 iMacs the ODD fan has the most cooling exact on the GPU, though speed the others too because keeping other innards cool helps the GPU.
Also, iMacs are Dust magnets.
GPU failure was pretty common with that model. Apple even ran an extended warranty program on it for a few years, but that program elapsed many many years ago. Sorry to be the bearer of bad news, but it is over 9 years old and it's probably best to start looking for a replacement system.
Have you blown the dust out of the intakes lately?
What temperatures does this App report? Especially the GPU.
This App can be used to speed up the fans, all my iMacs would be dead without it.
Never ever ever drop fan speeds below the speed that the Mac itself is calling for.
MacFansControl…
I have not done any of these things, but it does appear that it is an issue with the GPU. That makes all kind of sense because it generally happens when I am switching between displays. This is a taxing event for the GPU, and so I am going to heed your advice and go in the fan direction. Thanks.
Well, I downloaded the fan app and I turned up the value to "Full Blast", although I suspect that is not good in the long run. I noticed, not surprisingly, that setting pre-set speeds is only available in the pro version, which I will be going to next. However, that does me no good if I don't know what the recommended fan speed is. Care to share that with me?
Oh, WOW. These are much lower temps that I am running, although they have generally dropped more than 30F since I sped up the fans. Will attack the dust issue next. You have been a great help. I owe you a drink.
Yes, GPU failure due to heat is an iMac specialty. :(
30°F drop is good, but the longer it's overheated the less heat it takes to kill it off, so use as much fan as your ears can take. :)
Very pleased I could help, not much time left... stay well! :)
Oh, and yes. Apple's planned obsolescence at work here.
Colored Dots on iMac and then system freeze
