Introduction

This video guide shows how to disassemble the iMac in order to remove and repair the video card, then reassemble and test. As shown in the video, it is highly recommended to label all connectors to make them easier to reconnect without error.

Video Instructions

Late 2009 iMac 27" Video Card Repair — ATI Radeon HD 4850

Late 2009 iMac 27" Video Card Repair — ATI Radeon HD 4850

Video Source
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Conclusion

Not for the faint of heart and recommended only for someone who has a full day free and isn't afraid to tinker. Since the 2009 iMac is out of warranty and non-functional with a problematic video card, there isn't much to lose by attempting a video card repair. And while I cannot guarantee the "oven bake" method will work in every case, it did work in mine and in the case of many other people whose stories I have read online. Indeed those stories were inspiration for me to attempt the same repair. Even if one does not wish to repair the video card, this video still shows how to remove the logic board and video card and put them back in place.

31 other people completed this guide.

James Wages

Member since: 09/05/2016

1,080 Reputation

1 Guide authored

71 Comments

I've got a late 2009 27" iMac with the AMD Radeon HD 4850. About six months ago my iMac would occasionally not wake up from sleep mode and I'd have to do a hard reset. As time when on this started happening more often. Then the screen started blinking black and would finally stay black and I would need to do a hard reset to get the iMac working again. Finally, even with a restart the screen would remain black. The iMac was still running in the background but the screen was blank. In Googling the issue I found that it is a common issue with the late 2009 iMac with the AMD Radeon HD 4850. All my research pointed to the video card being the issue. In doing some more research I came across this repair guide by James and decided to give it a try as I really had nothing to lose. I took my time and worked through the video several times. Long story short, once I got the system back together and started it up I had video again. This repair guide was a life saver for me. Thank you James!!!

jcridge - Reply

It's wonderful to hear success stories like yours. I'm so happy to hear your Mac is back up and running again!

James Wages -

Same thing here, i have two imac 27" from 2009, one with i5 and one with i7. Both had a dead graphic Card so i baked one and put in an HD 6970 in the other one and it has finaly worked, both are back one live now!

Thank you very much for this video it helped me so much.

e-mail-patrick - Reply

Thank you for sharing your success story, Patrick! I'm so pleased to hear it!

James Wages -

Bin der Anleitung gefolgt, funktionierte auch bei meinem iMac:

iMac (27", Mitte 2011) A1312 mit GPU: AMD HD 6970

b.b. barnsi - Reply

Das ist schön zu hören. Danke, dass wir uns wissen lassen!

James Wages -

Hi, thank you for your excellent video. One question, how can I know if my GPU is dead? I have the EMC 2309 model. Today my iMac freezes the screen and never boot up again. It stucks in the Apple Logo only.

Thank you for your support.

Martín Vujović - Reply

Forget it, I deleted AMD drivers from Extensions library and the Mac startup normally. But can't use it because not using the GPU everything is extremely slow. I formatted for nothing :/

Thanks anyway for this great site!!!

Regards from Argentina.

Martín Vujović -

Glad you figured out how to solve your problem, and I wish my video card problem could have been solved your way! :-) But you will know when the video card fails because you will experience random freezes and sometimes you computer won't boot. You will also see strange blocks or other artifacts on screen. You Mac may also not wake from sleep. I experienced all these things and they went away when after I fixed the video card by oven-baking it. Best wishes!

James Wages -

Thank you for the video my mac is goosed the same as yours was so I have nothing to loose in chancing the repair .A couple of repair guys in my part of the planet say the repair only lasts months at best ,can I ask is your repair holding out.again thanks for the excellent video

Joe Doyle - Reply

Hi, Joe. I performed the repair in February this year. It is now June. No problems at all during those 3+ months. Keep in mind that I am not the only person who has performed this "oven bake" trick to restore their iMac's video card back to life. The following link is to the YouTuber who was the inspiration for me to try the trick, and he reported in Feb. 2017 that his iMac had been working fine for more than 17 months after his oven bake (which is precisely why I took the time and effort to try it):

https://youtu.be/9vPM41ZmLos

James Wages -

Your explanations and the detail you cover in this video is superb. I followed your instructions and completed it last night. So far, so good! Our iMac is operational again so we're back in business. Here's hoping it lasts for a long while. I think I will be buying and storing a replacement video card for if/when it happens again. Hopefully the next time I do this I will get it under 4 hours.

Thank you, James, for this brilliant video!

Dean Bolton - Reply

Thank you for your kind words, Dean. I'm very pleased to hear the video card bake worked for you. Buying a new card would probably last longer than the "bake fix" but in my personal experience, it lasts 3 years. Three years after buying my late 2009 iMac, it developed the video card problem. Apple replaced the video card with a new card, but 3 years later the same thing happened. I would assume the same would be true of any new replacement card of the same model. Whether a different model card would fair better is anyone's guess, but keep in mind they may not fit perfectly if you try them, and there could be thermal issues as well if they run hotter than the stock card. Best wishes!

James Wages -

Hi, my story is in away similar. I am still not sure if the GPU is the issue. Here is what happened:

Yesterday when copying a large video file the estimated time begun to increase. I left my computer for some time. After returning the screen was black with a white spinning wheel.

After some time I shut down the computer pressing the power button. When starting again I could hear the chime then the screen went white and stayed empty.

I connected a USB keyboard and tried various combinations:

Command-R for recovery

D for diagnostics

Then I connected and external bootable drive and pressed Option at start. The same then with a bootable USB stick.

Finally I pressed T to go into the Target mode.

Each time I could hear a chime and then the screen went white and stayed like that.

I haven't ever seen any artifacts.

What is your opinion? Is it a faulty graphic card and it makes sense to replace it or not.

Thanks.

Pawel - Reply

I've read many different reports from people who say their Mac exhibited different things on screen, either artifacts, or totally white or totally black, and sometimes with vertical or horizontal lines. Sometimes there are no screen anomalies but the machine just freezes. In almost every case the culprit is that silly video card. The design of that card is faulty. It would be nice if we could just swap it out for a different card, but the cards that don't appear to have the same fault won't physically fit in the iMac. So we either do the bake resurrection trick or get rid of the Mac and buy a 2015 or later edition. (I have a late 2015 edition 27" 5K iMac at the office and it's very well made -- never had a problem with it -- and it runs cool too.) So even if you "replace" your video card, the same problem will occur 3 or so years down the line. Apple replaced my card 3 years after I had purchased my Mac due to the video card fault, but 3 years later it had the same problem, which is why used the bake.

James Wages -

The best way to recover a broken graphic card is to perform a reballing. I did it a year ago and still working perfectly. The main problem is that contacts between pcb and graphic chip don't work properly, because heat degrades it.

Keibert Falcon - Reply

Keibert, thank you for your comment. I agree that paying someone to reball the GPU chip would probably last a bit longer than the oven bake shown in my video; however, I know from experience that even a brand new replacement video card only lasts about 3 years due to some defect in the design of the card itself. So basically you get 3 years out of a new card, perhaps less out of a reball and a little less, perhaps, with an oven bake. But the cheapest overall solution (costing you nothing but time) is the oven bake. Some people have reported going more than 17 months on the oven bake, so it's not a bad solution for those who want to avoid paying anything.

James Wages -

Having the same problem with my iMac 11,1 (27" i7 2.8 GHz late 2009), I will try this soon. But if this doesn't work, I surely need a replacement card. Which video cards are compatible to a ATI Radeon HD 4850 512 MB? Just in case, no 4850 is available.

Reiner Kief - Reply

Reiner, thank you for your comment and question. I have no experience testing a different video card, but I have read that some newer cards from 2010 and 2011 iMacs will function properly in the 2009 iMac. HOWEVER, I have also read that the physical size of those newer cards is not 100% the same as the stock 2009 video card, which means you may need to do a little cutting if you want to put a newer card in your iMac. Another potential downfall is the fact that those newer cards are faster but draw more power and generate more heat as a result. As such, I can only advise replacement with the same video card. And if ever you decide to get a new iMac, the late 2015 and newer 5K models are great. I have a late 2015 5K at the office. It runs cool and fast, with no video card issues to date. Best wishes.

James Wages -

Hi, I just wondered if the problem doesn’t lay in the thermal paste that’s too old and dried, because of the over heating ?

My son got a old PC from his cousin and we cleaned it from the inside dust, and therefore, I removed the heatsink of the CPU, but when putting it back, I didn’t bother of putting some new thermal paste. So the computer would just work for a few seconds and stop.

Same thing is happening with my iMac, it works, but the screen goes black in just a few minutes, often before the startup has ended.

So there could be a overheating problem in the GPU simply because the thermal paste is out of use ?

It seems too simple ;-)

mraj - Reply

No. I actually did 2 bakes of my video card. After my 1st bake I replaced the thermal paste, but the video card exhibited the same problem 4 months later. If it was the paste, as you surmise, the problem would not have recurred after 4 months. And by the way, after my 2nd bake, the machine is still going strong. I’m into my 5th month of use now. If you open my video in YouTube you will see a link in the description to my 2nd Bake video. Best wishes.

James Wages -

Hi James, thanks for the great video - especially for the detailed instructions! Your video encouraged me trying something I’d never thought of doing myself as a complete layman. The history of my iMac is about the same as yours - I had my graphics card replaced in 2014 and it lasted until 3 weeks ago.

I followed all your steps carefully, applied Arctic Silver 5 to the GPU and MX-2 to the chips, using about 3 grams of the latter. I must admit that while reassembling I damaged some of the contacts of the v-sync-ribbon-cable in the top left corner – the one that broke off in your second bake.

The reason why I’m telling you all this is because since the first reboot the display looks perfect, but the fans or at least one of them is running at full speed. The main noise is coming from the upper right – graphics card corner. I did the SMC-reset as suggested by Apple itself, but that doesn’t help. Would you have any suggestions?

Thanks a lot,

Ulli

Apfelgarten - Reply

The v-sync ribbon cable you mentioned damaging would not affect the fan speed, so it’s clearly something else. If you forgot to insert any one of the many connectors, or if you inserted one improperly during your reassembly, such could very well cause fans to ramp up. But it would have had to have been one of the connectors pertaining to a temperature sensor. If re-opening your iMac is troublesome (and you and I both know it is), you could opt to just use a software solution to control fan speed. There’s an app named “smcFanControl” which works fairly well. “Macs Fan Control” is yet another app you could consider. But if you simply cannot rest until the root problem is solved, then you will have no choice but to re-open your iMac and check the tiny connectors (those leading to temperature sensors).

James Wages -

Gee - this is somewhat embarrassing! I had actually taken the shortcut and disassembled the graphics card while leaving the logicboard at its place, so there was no need for unpluggimg all those connectors. Now I opened it up again and found no connector attached to the “HDD Temp” socket! And - what’s even worse - I simply can’t find any surplus cable. What’s going on… I guess I’ll have to take the long ride now.

Apfelgarten - Reply

You say you cannot see any connector attached to “HDD Temp.” Simply locate your hard drive (upper middle area) and you should then find a pair of wires attached somewhere on the hard drive, which is the temperature sensor. Following that wire pair until you see the disconnected connector dangling somewhere, then reconnect it.

James Wages -

James,

believe it or not - I do not have a hard drive temperature sensor cable! Is it because of the model (late 2009 - 2374) or the HDD-manufacturer or because I had given the iMac away for a repair cost estimate before I started my own repair attempt - I don’t know. I think it is virtually unthinkable that I could have disconnected such a twisted cable unintentionally on both ends. I thoroughly checked the inside, tilted the logicboard, used a torch and a buddy for help, I watched several videos and read through plenty of repair guides … no chance.

Apfelgarten - Reply

All 2009 iMacs have the temperature/thermal sensor cable attached to the stock HDD. You can see that connector in Step-10 here:

iMac Intel 27" EMC 2309 and 2374 Hard Drive Replacement

James Wages -

Thanks for the nice tutorial! Had the same issue with black boxes appearing on screen, and finally it wouldnt even boot up, but hangs on apple logo. Did the bake, reassembled, but no picture at all appears on the screen. There is no chime upon boot, but the system appears to boot quite far otherwise. The backlight brightness can be adjusted from the keyboard for example. Rechecked all connections twice… Any ideas what to try?

Mikko Parry - Reply

Mikko, I’m sorry you are having problems after your bake. Because of the complexity of the procedure, any number of things could have gone wrong. For example, it could be that you simply neglected to connect a single connector. Or it could be the video card itself wasn’t secured well enough into it’s socket after your bake. You probably would have noticed if you broke a cable (especially those thin ribbon cables) when you opened the iMac, so it’s probably not that but breaking the ribbon cables can cause a black screen. It’s probably just a loose or missing connection. But the bad news is that you’ll need to remove the display again in order to verify.

James Wages -

Bought my iMac in 2009 and it worked flawlessly until just before Christmas. I’d upgraded the memory and replaced the spinning rust with a SSD in July of 2017 and then it stopped. Just finished the baking of my GPU and it went from a broken iMac to a working one.

Thanks for the useful guide. I didn’t bother removing the motherboard on mine, but just used your 2nd video as a template. In the intervening time between it breaking and me fixing it, I had to get a replacement, so now I’m in the enviable position of not knowing exactly what to do with my working old iMac now, but I’m sure I think of something.

Once again, many thanks on the really useful and clear video instructions.

Jimmy Aitken - Reply

Thank you for sharing your experience, Jimmy. I’m pleased to hear the bake worked for you. Removing the motherboard can make it easier to replace the BR2032 PRAM battery, but replacing that isn’t absolutely necessary. You probably wouldn’t get very much if you tried to sell your old Mac, but if you have a family like I do I’m sure you can put it to good use in your home. If not, be sure to donate the machine rather than discarding it. One man’s trash is another’s treasure!

James Wages -

Can i Ask if i have problems with my iMac from 2009 and my screen when starting up has yellow vertical lines and after a while it has yellow smal squares and it stops and cannot go any further ! When i use shift when i start my computer i can go and use my computer but it still have the yellow lines across the screen! And after a while the scene freezes so i haveto restart again. can it be the same problem with the video card? Would be very grateful for any help! :-)

Timmy - Reply

Hi Timmy, yes I have heard stories similar to yours. You definitely have a video card problem and the bake would work for you. Just make sure you follow my instructions, especially about replacement thermal paste. Please also note that I have 2 instructional videos on the subject. The video above (here in iFixIt) shows my first bake which unfortunately lasted only 4 months. I then made another video of my 2nd bake, where I did not remove the entire logic board, and my iMac is still going strong on that bake. On that bake, I changed the type of thermal paste, so perhaps that contributed something positive to the bake repair. Please watch my video above on YouTube, then check the text Description underneath it for the link to my 2nd Bake video. You may also want to read the experiences of others in the Comments on YouTube. I reply to every comment and you’ll find a lot of useful tips and advice there. Best wishes!

James Wages -

Thanks!!!:-) Where do i get the termalpaste that u bought from greece? We don’t have amazon in sweden!:-/

Timmy - Reply

You can buy K4 & K5 Pro direct from the company in Greece who makes it:

http://www.computer-systems.gr/content/p...

The round container in the photo on their website looks different from the lip-balm dispenser in the EBAY link you provided for me, but it contains the same thermal compound. Since it was faster and cheaper for me, I used Amazon here in Japan to buy it. For you, either direct from the maker or EBAY will work — whichever you prefer.

James Wages -

Yes, that paste (both kinds, K4 & K5) you linked on EBAY is exactly what I used in my 2nd Bake. And as of today, that 2nd bake has lasted 7 months and the iMac is still being used daily (even for games) without a single problem.

James Wages -

Hello,

After following your tuto, I have the CPU fan that runs very fast. [|According to Macs Fan Control, the CPU fan is not spinning (]https://i.imgur.com/k9wnm6n.jpg) , so my guess is that I actually lost control of it, not sensor related, because using MFC I cannot manage it.

Do you have an idea of which connector do I need to check? I already open it a second to check every single one. I don’t know how to stop that fan…

Kevin H. (Kash) - Reply

Kevin, it seems that you merely forgot to connect one of the many connectors you disconnected in accordance with my video. I agree that opening your iMac again to find that connector would be troublesome and time consuming. As such, I recommend that you just set your CPU fan to run at a constant speed using Macs Fan Control. To do that, just click “Base sur Ambient” and then a little sheet will drop down, allowing you to choose a “Constant RPM value” (the top-left radio button in that sheet). Minimum is 1200rpm, which should be good enough, but if you want your machine to run cooler, you can bump it to 1500 without increasing the noise too much. Please let me know if this helps.

James Wages -

Oh How Do I thank Thee!!!

Followed your instructions to the Tee. Perfect - My iMac is back - Me very Haappy!!

Thank You! Thank You!

Rajeev Bhalla - Reply

Thou art welcome, Rajeev! :-) Thank you for telling me of your success. Best wishes to you and your resurrected iMac!

James Wages -

The thermal pads and thermal grease need to be reapplied right away before video artefacts became to frequent and get worse. The OEM thermal paste that Apple uses does not conduct the heat away efficiently at all on these hot amd cards.

Marcus S - Reply

Thank you for your comment. While I agree with you that Apple is sadly using inferior paste, the tragic reality is that your average Macintosh buyer is not equipped to do that themselves, nor are they aware of the need for it. Even so, not all Mac models are afflicted by this video card plague. The fact is that the 2009 through about 2012 (2013 too?) models of iMac used a video card that was not designed well. That combined with subpar default fan speeds contributes to this problem of freezing and video artifacting.

James Wages -

I just wanted to know if a 21.5 inch iMac’s graphics card would work on a 27 inch iMac?

Ed Saucin - Reply

I’ll just finish saving up some money and try it out. If it doesn’t work, illl just sent it back.

Ed Saucin -

Because I do not have first-hand experience with using a video card from a 21.5” iMac in a 27” iMac, I cannot offer you any compatibility guarantees. But assuming you have a ATI Radeon HD 4670 card, be aware it is a very different shape than the ATI Radeon HD 4850 in my late 2009 27” iMac. Just Google those card names, then click on IMAGES and take a look for yourself. Because of the shape difference, the heatsink wouldn’t fit right. And also note the ATI Radeon HD 4670 card only has 256MB of VRAM.

James Wages -

First: Thank you for your time in creating such detailed ,clear & helpful videos!

Second: My 27”2009 Imac has suffered similar fate as most stories noted above, so I have read various articles and preparing for the bake off, and had one main question.

Is there any legitimacy in attempting to use a heat gun to the GPU instead of baking, while covering all other components in tin foil to possibly prolong the life of the video card while following all other steps accordingly. If so, is there any particular amount of time I should keep the gun running directly to the GPU? It has a 250c & 450c setting.

Carlos Rincon - Reply

Thank you for your kind words, Carlos. I cannot offer you specific guidance on the heat and duration of using a Heat Gun instead of the oven bake method, simply because I myself have never tried the Heat Gun method and therefore cannot vouch for its successfulness. THEORETICALLY, it very well could be even better than the oven bake as the heat would be localized to the GPU only, rather than the entire card. However, you must be very careful with heat guns as some are hot enough to melt the solder, and when that happens SMD components will start to float around, potential creating more trouble for you than you had originally. The Oven Bake method is only 200°C, which isn’t hot enough to melt even Lead solder, so there are no worries that SMD components will shift out of position. But 200°C is hot enough to repair whatever broken leads there are in the GPU die.

James Wages -

This is an excellent video, James. Thanks. I used it to bake the GPU on my mid-2011 iMac when the vertical green lines appeared and it failed to start up. It now works perfectly again.

Some of the motherboard connectors are slightly different in the 2011 iMac. Ultimately there were slightly fewer than on James’s machine, but the video gives all the info you need to figure it out. The ambient light sensor was very easy to remove on my Mac - lucky me!

I also didn’t need to remove the entire heat sink mounting assembly from the mother board. It was possible to remove just the video card and heat sink by removing the 2 torx screws that fix it to the motherboard and a single torx screw at the other end of the heat sink. In fact, it would have been difficult to have done it any other way.

Although marked ‘difficult’, I think it’s more ‘involved’ than hard to do. You just need to be methodical and organised, and don’t be put off by the depth of deconstruction/reconstruction - it’s a perfectly surmountable task!

graemebagnall - Reply

Thank you for your kind words and for letting me know of your successful bake! It marked this job as Difficult because it really does take a long time if you’ve never done it before, and it can be very intimidating for people with no experience whatsoever in dealing with electronics. But as you point out, if you are determined (and have the needed tools too), it is certainly not insurmountable!

James Wages -

All you need to do to remove the GPU card and heat sink are:

1-Unplug the heat sensor (plugs straight in - on the back of the motherboard opposite the LCD heat sensor).

2-Remove the screw that holds the heat sensor to the frame in the upper right corner.

3- Remove the three screws holding the GPU to the MB.

4-Unplug the GPU from the motherboard.

rockpiano54 - Reply

Thank you for your comment. Yes, I am well aware of that, and indeed, my 2nd Bake Video clearly shows the process:

https://youtu.be/6BJGLFCigdA

But that doesn’t eliminate the need to remove the motherboard if you wish to (a) replace the BR2032 PRAM battery on the back side of the board, or (2) clean behind the motherboard. But again, I made two videos, so the viewer can choose whichever method suits them. Thanks.

James Wages -

Great Guide, Did it!!!

THANK YOU!!!

I completed my repair in June 2017 and my monster (late 2009) is still running ;-)

NB

I left the mainboard inside, since I’m keeping it on wire most of the time. It all went fairly well.

lalatommy - Reply

That’s wonderful to hear. Thank you for letting me know. Best wishes to you and your newly resurrected iMac!

James Wages -

UPDATE

iMac is still running - happy user for 15 additional months now :))

btw. I’m using mac’s fan control. So for games I have the fans working quite hard. I was amazed by the heat that is produced. No wonder, having the fan run in normal mode causes trouble in many cases…

lalatommy -

Thank you for the 15-month update. I’m so pleased to hear your iMac is still going strong. So is mine. I too am using a software-based fan control app, running all the fans at about 2000rpm. I can hear them in a quiet room, but it’s better to keep the iMac cool inside than to keep the fans running at the stock speed and have something overheat. I’m still unsure if we’ll get more than 3 years out of the bake, seeing that even a brand new card from Apple, installed by Apple, lasted only 3 years in my experience, but who knows. Maybe all those series video cards just needed a little more time to bake before they were released into the wild. :-) Anyway, may your iMac give you many years of life! Best wishes!

James Wages -

just finished this repair. booted her up and we are off to the races again. pretty much followed the guide step by step. i chose to upgrade my GPU from a 256Mb 4670 to 1Gb 6970 (or so i thought). i didn’t bake the replacement but did remove it from the heat sink and cleaned and freshened up both compounds. labeling each connection to the MB was time consuming but well worth it upon reinstallation. took more time cleaning the LCD and front and back of the glass than reinstalling the board. got everything buttoned up. powered it up and loaded the OS. i opened “about this mac” and saw i was sold a 512Mb 6770 instead of the 1Gb 6970

thesidewalk - Reply

I believe you have a 2010 iMac? Glad to hear my video was helpful to you. Sorry to hear you were actually sold a 6770 instead of a 6970. Some people have asked me if it’s worthwhile upgrading the video card in the 2009 iMac (which is the one I have). I replied that I myself didn’t want to take the risk that the newer card might be hotter than the old, or that the newer card might not fit perfectly (depending on which newer card was chosen). It’s not simply a matter of fitting the video card but the heatsink as well. Anyway, thank you for letting me know of your success!

James Wages -

Dear James

Thank you for your posts. Have bought recommended supplies here in Riyadh and am soon going to attempt this fix on our mid-2011 27” iMac.

Problem: It is stuck in a never ending re-boot cycle, never gets beyond Apple logo and ¾ of startup bar loading.

Fixes already attempted:

*All Apple-suggested troubleshooting reboot combos.

* Local Apple repair couldn’t help (after taking $50 and keeping it for 3 weeks).

*Thought our problem could be RAM related so I tried all possible ‘configurations’ removing, re-inserting new/old RAM 4 and 8GB.

Question: Does this even sound like the graphic card is faulty and needs baking/changing?

Feedback/experience is much appreciated!

Greetings, Umm Mosa

Umm Mosa - Reply

Even though you have a 2011 iMac 27” and I have a 2009 model, the symptoms you describe are very similar to what I have seen. So yes, I do think that baking your video card may resolve the problem. It’s very unfortunate that Apple charged you $50 for nothing and made you wait 3 weeks too! That’s just horrible. You said you purchased the supplies needed for the bake, so you are good to go. But please also watch my 2nd Bake video if you haven’t seen it already: https://youtu.be/6BJGLFCigdA

James Wages -

Dear James, I've got a late 2009 27" iMac. I followed the disassembly procedure and after preparing the GPU and heat sink I was ready to reassemble. But the sensor connector that goes from the heatsink to the back of the motherboard now has a problem.

There are a green and black wire that end in a tiny black connector, but the black wire has broken off or become disconnected there. Can I try to reconnect it, or should I replace the wire bits, or replace the entire heatsink, or just give up.

If I just connect it as is, will the GPU not be reporting its temp, thus inviting the fans to blow at top speed? Please advise. - Robert

Robert Lloyd - Reply

As it turns out I reassembled the iMac; did not repair or replace the heat sink sensor and did not connect it to the MoBo.

The Mac started up completely. Before I baked the GPU, it would stall with the startup progress bar exactly halfway. It would start ok in Safe Mode.

Robert Lloyd -

Robert, thank you for your two replies. You really need to fix that sensor before you start using your machine full time. Can you shoot me a clear, zoomed in photo and post it to Flickr or DropBox or CloudApp, etc. and then post a link to that photo here so I can see it? That way I can better informed you about how to repair it. Thanks.

James Wages -

can you tell me if I can install another Radeon card with more memory in it or does it only work with the specific card, in this case the Radeon HD 4850?

jonathanjosecordeiro - Reply

Most other cards won’t be a perfect fit, even if they work. Newer cards may also run hotter, which is not something I can recommend. Beyond that, I cannot say much more because I do not have first-hand experience with using a non-standard card. If you want to be 100% worry free, stick with the 4850.

James Wages -

THANK YOU! THANK YOU! THANK YOU!

My iMac was dead for over a year; it sat in limbo, in a corner, waiting for me to work up the courage to open it up. Your detailed videos helped me overcome the inertia of ignorance and fear.

**THANK YOU!** I watched both of your videos, purchased the tools from iFixIt and dove in.

I even experienced the RAM alarm beeping because on my first three attempts, I had not seated the RAM properly so your first video really helped there also (along with @mayer here).

I didn’t have any white thermal paste so I used red RTV. Had to work with what I had with the time I had.

My iMac is working again! Thank you so much for your detailed videos.

Inbtwixt Itall - Reply

I’m so happy to hear of your resurrection success! Best wishes to you and your revived iMac!

James Wages -

I did my first repair 13 months ago before the second failure. after a second bake i seem to be back in business! thanks for the helpful guide!

Brad Pinder - Reply

Thank you for reporting your success story, Brad. To clarify, you performed your very first video card bake (at 400°F/200°C for 9-10 min.) 13 months ago and recently your Mac showed the same video card failure symptoms again, prompting you to perform a second bake? If so, what thermal paste did you use on your first and second bakes? I ask because my first bake lasted only 4 months, and that might have been due to the very old thermal paste I used, and the fact I didn’t clean off all of Apple’s stock thermal pads which cool the video memory chips. But on my second bake, which has thus far lasted more than 14 months of daily use, I used K4 Pro and K5 Pro (from Greece, not electrically conductive) and I believe that has made a positive difference. Best wishes.

James Wages -

Hi James, i used a fairly generic thermal paste; silver containing for the main chip and a non conductive for the side chips/blocks. The bake was at 200 for 9 mins. the recent failure was exactly the same as the first (two horizontal pink bands across the screen, and failure to boot). My usage is pretty light, so will see how we go this time!

Brad Pinder -

That sounds similar to my first bake. I used an old tube of Arctic Silver V on the GPU and an old, generic, previously unopened, non-conductive paste on the memory chips. But again, I didn’t clean off the old thermal pads that were on the memory chips and just applied that non-conductive paste over the remaining pads. After my 2nd bake I did a thorough cleaning of all the thermal paste material, and then I used freshly opened and new K4 Pro on the GPU and K5 Pro on the memory chips (which is a thick paste that acts as a replacement for thermal pads). Not sure if my first bake lasted because I didn’t clean off the old Apple pads on the memory chips, or if the GPU simply needed two bakes to finally come back to life. But as I said, I’ve gotten about 15 months on my 2nd bake, and that is with daily use of the machine, including GPU intensive games by my son. I also use smcfancontrol to keep the fan speed higher than stock. Best wishes to you and your twice-baked iMac!

James Wages -

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