Imac 27 EMC2429 randomly reboots

[MvdLans]

Hola!
After an initial thread about my Imac randomly keeping restarting I opened up the machine today. Its a mid 2011 Intel 3.1 gHz I5.
There was no excessive dust in the case. I disambled the GPU and renew the thermal paste. No discolouring or whatsoever on the GPU.
The power supply seems correct as well.

Oh, and the 4 leds are shining bright as well inside the case!

So it's really getting quite annoying cause the problem is intensifying....

What's happening:
- The machine boots, I get the chime
- Sometimes it reboots before giving the pasword, most of the time afterwards.
- After the pasword sometimes the desktop icons (pictures, docs etc) load faster than other times???? Don't know why... Anybody a clue?

So most of the time the machine makes a loud clack and the screens goes black. Sometimes it happens 5 times before getting a stable machine, sometimes more...

Or when the machine is working good, it goes to sleep. When I awaken it it gives right away the clack and reboots.

A lot of these machines had GPU problems (I have the 1Gb Radeon) but my screens doesn't have weird stripes, or other strange issues. It plays movies and demanding games quite well. So I doubt that it is the GPU.

Someone from this forum kindly helped me with the ASD file for my machine but the tests didn't showed any major errors......

Does anybody have a clue cause the machine is making me nuts!!!

 

[Fishrrman]

I'd try removing and re-seating the RAM.
Is it the factory-original RAM? Or... replacements?

I'd also suspect the power supply.

 

[mikehalloran]

The three usual suspects:

1) An old bit of code is causing a conflict while booting. If it boots fine in Safe Mode, this is your likely cause.

2) Have you ever replaced the NV RAM battery?

Reset the NV RAM. If that fixes it for awhile and the problem comes back, replace the battery. If you have an HDD in there, use a high-heat BR2032, $7 for one; $8 for three on Amazon. If you have an SSD only, a common CR2032 is fine.

3) It can also be the boot drive. Passing the SMART test in Disk Utility means nothing. I have replaced dozens of HDDs in 2009–2014 iMacs to fix problems that passed SMART.

TechTool Pro is a much better tool. If you bought AppleCare with your 2011, there was a copy of TechTool on the CD. This is a typical picture of a drive causing major problems but passing SMART in Disk Utility.

 

[MvdLans]

Well it seems to have been the GPU!!

I have put the GPU in the oven for about 10 minutes at 200 degrees and the machine is back up and running!!!! Very happy!!

But again this is a major issue with Macs..... This is my 3rd GPU I've fixed in my oven!!

Is it really that hard to make a GPU that can take some abuse Apple??!!??

 

[Fishrrman]

"Is it really that hard to make a GPU that can take some abuse Apple??!!??"

I take a guess ... could have something to do with the "environmentally-safe" lead-free solder that they use these days...

 

[mikehalloran]

Is it really that hard to make a GPU that can take some abuse Apple??!!??

Did Apple make this?

No

Is it a known issue on the 2011?

Yes

Is your iMac 8 years old?

You tell us

Did you get it fixed?

Yes — so quit whining.


My recommendation to pull and replace that spinning heat pump still stands.

How many 2011s that I still service have ever had this known issue?

Not one. I'm betting it's because I replaced the HDD in every one of them in 2015 when SSD prices started coming down.

I take a guess ... could have something to do with the "environmentally-safe" lead-free solder that they use these days...

Interesting guess. The constant expansion and contraction of the components due to the wide heat range these go through is certainly the cause (also explains why this rarely happens after the HDD is removed). The solder joints could easily be the fail point. That baking works indicates this might be so. Many lead-free solders used in electrical work have a melt point of 190°.

 

[MvdLans]

Did Apple make this?

No

Yes they did. I've been a Mac lover for over 15 years but that aside I've never had these problems with a Windows machine....

Let`s face it, I baked a Imac 2009, a Macbook pro 2009 and now an iMac 2011, there's something seriously wrong with the GPU's Mac is using........... Or the way they are cooling them!!

But I agree, I won't go back to windows!

 

[mikehalloran]

Apple did not make the GPU in your — or anyone else's — iMac. Although they have used different vendors, a 2011 will have one of three aTi GPUs.