iMac late 2012.... trying to find prob

[jtbauld]

I have had my iMac for a while and I love it.... I've always loved gaming but one of my games runs on windows so over the last 4 years I've had my system bootcamped. It works great. A month ago the computer decided to die and the hard drive (fusion drive) split. I had to fix that and without problems, I reinstalled osx and bootcamped it again. a week ago it died again so I thought the drive might be damaged... but I couldn't install osx again... halfway it just freezes and restarts the system. funnily enough, it will install windows fine... but once I load the Bootcamp drivers it died halfway through and wouldn't start up so I had to wipe and reinstall windows again... later finding out the video card driver (i have GTX 680MX 2GB) is what was causing the prob... so as long as I just use the generic windows driver it worked. obviously, i haven't been gaming and I have been in contact with Nvidia and they think my GPU is shot. I was looking at replacing the logic board but I wanted to do some research before spending the money on an old system but I do love it and it does everything I need still, well up to this point. Any help or pointers would be awesome. here is a list of the things which I have tried:

1- Internet Recovery (stalls halfway and usually restarts)
2- Install from bootable USB... tried different versions of OSX, no deal
3- holding alt or option to get the recovery which it doesn't have
4- held D to do the diagnosis.... gives an error (more or less it doesn't exist)
5- I had it apart and cleaned everything except removing the heatsink
6- windows currently installed and working minus the GPU driver

 

[Cory Cooper]

Hello and welcome.

From your description, it sounds like a iMac (27-inch, Late 2012), correct?

It does sound like a logic board/GPU issue, as that would cause the issues you are experiencing. It would be your decision whether to replace the logic board, as that may/may not fix the issues, if there are other components contributing.

C

 

[jtbauld]

Yes, you're correct it's the late 2012... I've been using this for nine years and I have pushed it always so I'm quite sad because it does still do what I need... I opened it up and it needed to have been cleaned long before now which I think caused the prob (overheating). I have a logic board on the way along with another 16GB of ram as it can do with the boost. do you think there are some things I didn't try?

 

[jtbauld]

Hey Cory,
Not sure if you can shed some light on this.... I bought the new board (used) and installed it and works great again but upon switching out the heatsink and processor I noticed my problem. The thermal paste on the video chips, 4 of 7-9 the locations were dried and cracked. Seeing this I went through with the replacement but later thought that if I replaced all the thermal paste would it of worked?? what do you think? i am looking at selling the old board for parts now but i am curious

 

[dchyde]

I have a mid 2011 27” iMac and about two years ago it started developing video issues until it would not boot to any OS, just a white screen.
After a lengthy investigation it lead me to believe it was a faulty GPU card. I searched the web and after watching many videos and reading forum comments, I decided to repair the GPU, working along the examples in two video clips.

Link 1:

Link 2:

I was a bit dubious about the process but spending fifty years in the electronic construction and servicing field, I decided to give it a go.
I was doubtful about the baking of the GPU card in the oven but constructed sufficient supports and did it. I spent the next day reassembling the computer and could not believe my eyes when I powered it up and screen came to life as good as before. I really needed the old mac to be able to run legacy applications. I would recommend the process even though there is only a fifty fifty chance that it would work.

If you need and more info, just reply.

 

[jtbauld]

Thanks for the reply I am going to watch the videos now. your video card is separate from the motherboard as mine is all one unit. But just from looking at the video card on the video, it seems the same arrangement of chips. I have never swapped out a chip but maybe if I need this in the future it's something I will look into.

 

[jtbauld]

So it's been a year almost and I swapped out the board and success all worked fine so it seems the GPU was shot... and looking at the dried thermal paste it's a good bet that was the issue..... Since then I just turn my iMac off a day ago just because I was going to be out for a day... when I got back and turned it on I am getting 1 beep every 5 seconds which tells me its bad RAM.... side note I put more ram in when I swapped out the board just because I figured it would help the old lady. so I did the reseating of the ram... nothing... tried testing one stick at a time... nothing... swapped to my old board... the same thing... so its either all 4 sticks of my ram are shot.... the power supply or the CPU.... everything was working fine before the shutdown... any ideas?