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My iMac is now out of warranty after it has gone to the service centre twice to replace a multitude of issues relating to the faulty display. This time the issue has been isolated to the video card. Could someone show me how to replace the video card and if anyone has suggestions on how to solve the heating problem, which I understand is a known issue. Thanks!
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There are three video boards used in this system. Depending on your model here are the part numbers:
As to replacing the video board you will need to completely remove the logic board from the system. There is no IFIXIT guide to do this fully, but this guide will get you mostly there: Installing iMac Intel 27" EMC 2429 Dual Hard Drive Kit.
As to your heat problem:
This iMac was the first to use the internal thermal sensor in the HD. If you replaced the HD without using a special cable or one of the newer HD which now have the compatible sensor you will find the systems fans will ramp up to full power and stay in that state. Some people attempted some software hacks which to manage the fan speed we found this solution was not very reliable as it didn't allow the discreet fans to run so the GPU would over heat burning it out. Which is what likely happened to you.
So what to do here?
You can get this OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade or you can replace the HD with a newer one that is compatible like the Seagate 3.5" SSHD drive. Make sure the box has an Apple logo on it (the newer version).
Before you do anything you might want to see if the sensors and fan units are working correctly. Using a second Mac putting your system in Target mode as the bootable disk install Temperature Gauge Pro. Once you have it installed you'll need to also setup screen sharing so you can see your system. Now restart your system and your second mac then access yours via screen sharing you should then should be able to see what your systems thermal sensors and fans are doing. Take a snapshot and post it here when its running on the hot side so we can see whats happening.
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Thanks for the feedback.
Just to clarify a couple of points for everyone's sake.
Mine's the #661-5968 - AMD Radeon HD 6970 (not 6770), 1GB.
I've been having this issue twice, both of which were fixed by Apple official RV by replacing the video cards. Researching online, it seems this is an inherent design issue dealing with heat buildup, with range of iMacs. Coincidentally, it failed on this last occasion when the weather was hot and I did not turn on the aircon in my already hot room.
Not sure if this card is still in production. I did read somewhere of some techies repairing a video card probably damaged in a similar manner. Wonder if this is relevant: https://www.youtube.com/watch?v=hoxR_TVE...
As for the heat solution, I will certainly look into the OWC In-line Digital Thermal Sensor for iMac 2011 Hard Drive Upgrade
Any thoughts appreciated.
Sorry I forgot to paste the correct model number in my haste (now corrected).
It's possible the GPU solder joints have failed (cold solder joints). Sadly, I'm not in agreement with Mark Sicat's solution. Yes, it can buy sometime as you are reflowing the solder connections under the BGA chip so it can appear to revive it.
The problem is the solder has already decomposed from the excessive heat so it will re-crystalize again in short order causing the cold joint issue again.
So the Q is what to do here? The correct way is to completely remove the chip clean off all of the old solder on both the chip and the PCB and apply the correct high temp solder (re-balling) the chip then re-applying the GPU. This is too big a job for most of us (including me) and you do need some special tools and fixtures which are costly.
Given the availability of the video board I would just replace it and make sure to use a high quality thermal paste and making sure the fans & heat-sinks are clean and working correctly.
But lets step back for a moment here, this system has a very good cooling system (over the older '09 model in your link). The problem is people tried to control it failing to understand how Apple designed things so they think their way is better! Sorry Apple did a good job. Our tampering with their design messes things up. The start of it was in some ways Apple fault here as they used custom firmware in the HD's to get better performance and access of the internal thermal sensors that only a year before many of the HD makers added for product QC not system use! So we forced in HD's that didn't link up with the Apple SMC services. So we messing things up by over-riding the SMC service! And in doing so we failed to deal with how SMC thermal control was designed to work.
The other thing that comes to play is keeping the systems vents clear so the system can breathe and keeping the system clean of excessive dusk build up.
Your usage of the system in a very hot environment could have just been the straw that broke the camels back here. Another cause and effect is the applications being used. Heavy graphics apps (i.e. video editing & games) can also push a systems GPU. Both of these issues are also a problem with Windows based systems too not macs alone here.
Good pointers there. I've found a good RV and will be getting the GPU resoldered or replaced, to see if that can be salvaged. The cost of a replacement video card online is more than half of what the resale market of the unit, and even then I'm not even sure if I will be getting the new one or a reconditioned card. So baby steps here before the big decision. Thanks for all the feedback Dan!
No problem, Hope it all works out in the end. If this answer answered your question please remember to rate (score) and mark it accepted.
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my graphics card is replaceable w/o removing the logic board
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