Re-Apply iMac 7,1 GPU thermal paste

Discussion in 'iMac' started by jimmy43, Jun 29, 2012.

  1. jimmy43 macrumors member

    Joined:
    Apr 9, 2008
    #1
    I'm trying to find some instructions online about how to get to the video card of an iMac 7,1 (24" core 2 duo aluminum), so I can re-apply the thermal paste. (trying to lower temperatures as I have in another post here)

    I found this video:

    http://www.youtube.com/watch?v=NWGsDrYcS9s

    I'm not sure if this is the same model. I'm not even sure where on the logic board the video card is?

    So far I have the screen off and I can see the logic board, but I just want to make sure I'm on the right track. Anyone have a link to a tutorial or a video, or any tips?

    thanks :)
     
  2. Johnf1285 macrumors 6502a

    Johnf1285

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    #2

    At 4:25 to the corner of the super drive you'll see the GPU. The 24" is extremely similar to this 20", just slightly more room inside.

    The heat sink bracket for the GPU is also the bracket for the CPU, fastened to the logic board. You should be able to reapply the GPU thermal paste, but may need to do the same for the CPU.

    Can't say I've ever done this, but I have been inside of the 2007 20" for a hard drive replacement and inside of a 2010 21.5" and 27" for SSD upgrades. I've also built a number of PC's in the past dealing with thermal paste applications.

    Hope this helps, good luck and take your time. The parts are fragile!
     
  3. jimmy43 thread starter macrumors member

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    Apr 9, 2008
    #3
    Thanks for the quick reply.
    I just noticed that there is a tiny AMD logo right by the corner of the super drive where you pointed out it would be. So that should be the GPU (on the under side of the logic board damn!).

    Would you have any tips on re-applying thermal paste? I was thinking of going with the Arctic Silver Thermal MX-4 Paste. Would 1 tube be enough for the CPU and the GPU? (since you are saying I will have to re-do the CPU as well)

    thanks!
     
  4. joe-h2o macrumors 6502a

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    Jun 24, 2012
    #4
    Since the heat sink is for both CPU and GPU if you remove it from the logic board you'll have to replace the paste on both at the same time.

    Spread it on thinly, but evenly. You don't want a huge gloopy mess, or for it to be lumpy or patchy.
     
  5. Big-TDI-Guy macrumors 68030

    Big-TDI-Guy

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    #5
    Ground yourself to prevent ESD.
    Before starting, used compressed air / anti-static brush to remove dust in the area, fans, heat exchangers.

    Gently remove the heatsink, don't pry with metal, it may be on there really tight after this long - so don't force it.

    Use a good solvent (isopropanol, or acetone if you're careful) and some cotton swabs, and remove all the old compound from both surfaces.

    Follow the instructions on Arctic Silvers website for application of the compound.

    Profit.
     
  6. Johnf1285 macrumors 6502a

    Johnf1285

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    #6
    I would suggest MX 4 thermal paste.

    Arctic Silver is capacitive and could cause issues if it bridges any traces, especially when dealing with a mobile GPU (things are really crammed onto that board). I would imagine that GPU die probably doesn't have a heat spreader on it, I don't know how safe it'll be using AS5
     
  7. joe-h2o macrumors 6502a

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    #7
    I wouldn't use acetone anywhere near a computer - there's a reason I use it in the lab as a general purpose cleaner - it dissolves plastics. If you spill any on the chip housings of anything on the board you might damage them. Stick to isopropyl alcohol.
     
  8. Big-TDI-Guy macrumors 68030

    Big-TDI-Guy

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    #8
    Barring the display and plastics on the exterior - there isn't much Acetone will really hurt, especially when applied via swab. I have yet - in my life- to ever dissolve a chip or PCB with acetone. Plus, acetone is way more polar, and kicks the crap out of isopropanol with this type of cleaning. Most of the plastics on PCBs are Nylon or PPE - not much ABS is there.
     
  9. joe-h2o macrumors 6502a

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    #9
    Indeed, if you're careful it is a great general purpose organic solvent that will dissolve the things that other solvents turn up their noses at. If you're a bit free and easy with it, it can cause issues, even if you think it's all dried up. It's just like getting a PCB wet - most things will be ok if you're careful and so on.
     
  10. Intell macrumors P6

    Intell

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    #10
    May I ask why you're wanting reapply the thermal paste onto the GPU?
     
  11. jimmy43 thread starter macrumors member

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    Apr 9, 2008
    #11
    Thanks for the replies everyone!

    I am going to use Arctic Cooling MX-4. Here is a link:
    http://ncix.com/products/?sku=55958&vpn=MX-4T-4G&manufacture=Arctic Cooling

    I was also going to use this solution to remove the existing paste:
    http://ncix.com/products/?sku=18558&vpn=ACN-60ML&manufacture=Arctic Silver

    A bit steep for both but I believe I can get them pm'ed down to 5-6 bux each.

    I've got the whole iMac now dissasembled and the GPU removed. I would post a picture but it's at work! Overall, it took maybe 1 hour, including labelling all the cables and pieces.

    Removing the GPU was tricky, I did not actually take off the heatsink from the logic board, I just gently pulled the GPU out of it's slot as I loosened the screws holding the heatsink on it.

    The GPU itself is a tiny square board. Now I've got the GPU all by itself, and the bottom of the heatsink exposed, so I can remove the paste on each one and put on the new one.

    Quick question, should I put paste on the bottom of the GPU only, or the heatsink, or both?

    I will try to get some pics up here for people who are interested in doing the same. Putting this thing back together is going to be a real joy :p

    ----------

    You were helping me in another thread, where I was asking about ways to underclock the GPU on this iMac to get it cooler. Since that path didn't work out, I thought putting on some better thermal compound would drop a good 5c off the temps, which would make it good enough for work usage!
     
  12. Intell macrumors P6

    Intell

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    #12
    The GPU already runs well within the limits set forth by AMD. Even when it is under load in a hot room with the fans at a default speed.
     
  13. Scythe5 macrumors regular

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    Jun 12, 2012
    #13
    My advice would be to leave it alone, but we are way beyond that. :)

    I'm not sure what you mean by: " should I put paste on the bottom of the GPU only, or the heatsink, or both?"

    The paste should only go between the chip and the heat sink. Use a small amount and use something to spread it evenly over the chip. (I usually use a used gift card to do this sort of thing).

    Too much paste is as bad as none at all.
     
  14. Big-TDI-Guy macrumors 68030

    Big-TDI-Guy

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    #14
    Usually, you apply the paste to both surfaces (after they are clean!) with a thin layer. I tend to apply more compound to the center of one side - (just a tiny droplet) so as the heat sink is put down - you can visually see whether or not its flat and centered.

    And yes - too much compound is bad. While it's very thermally conductive in a thin cross-section (as it's intended to be used), very thick fillets actually behave like an insulator. The other downside, is bridging any conductive traces if it extrudes too far, and not to mention it will capture dust over time.

    http://www.arcticsilver.com/pdf/appmeth/int/ss/intel_app_method_surface_spread_v1.1.pdf
     
  15. Scythe5 macrumors regular

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    Jun 12, 2012
    #15
    I've never head of applying to both surfaces. I took a look at the instructions you provide - they don't tell you to do that either.

    They say to apply the paste to the chip.

    They also say you can "tint" the heatsink. This is merely to fill in any microscopic voids in the surface of the heatsink. I wouldn't really count that as applying to both surfaces.
     
  16. Johnf1285 macrumors 6502a

    Johnf1285

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    #16
    In my experience, a bead of thermal paste on the CPU/GPU is ideal. I let the heat sink spread it out when I attach it. Just be careful that it gets attached and torqued down in one motion, don't let it slide around or come loose.

    For CPUs I generally do a bead about the size of a raw pea. For GPUs a grain of uncooked rice since they typically have no heat spreader.

    These methods always worked well for me. I rely on the pressure of attaching the heat sink to spread paste evenly.

    The last GPU thermal paste replacement yielded in 10c temperature drop under full load on a MSI Twin Turbo III HD 6950. I was shocked! Was using MX 4. Totally worth it.
     
  17. Big-TDI-Guy macrumors 68030

    Big-TDI-Guy

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    #17
    The "tinting" as you called it, is what I referred to. It actually does improve performance, as you brush the compound in from different directions. This allows you to better fill the micropores on the surface - especially if there is a grain on the metallic surface. When you just mate to the chip with compound on one side - the extrusion usually flows from the center-outwards. This can result in compound failing to fill in some of the voids on the mating surface.

    I use this technique on 2.4kw arrays that have a thermal interface 1/3rd the size of a CPU. These things cost an average of $7,500.00 each - and have yet to experience a failure related to thermal runaway.

    Granted, these diodes have an order of magnitude more power being dissipated in them, but I figure what's good for the goose...
     
  18. Johnf1285 macrumors 6502a

    Johnf1285

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    #18
    What he said :D
     
  19. awer25 macrumors 65816

    awer25

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    Apr 30, 2011
    #19
    I agree. Arctic Silver 5 is still held in high regard because of it's long time run as the king of thermal pastes. However, there are drawbacks such as the capacitive issue and the fact that it takes 200 hours to cure.

    MX-4 has the same performance without either of the two issues above.
     
  20. jimmy43 thread starter macrumors member

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    Apr 9, 2008
    #20
    Some photos!

    [​IMG]
    [​IMG]

    Waiting for stock on the thermal paste..
     
  21. Big-TDI-Guy macrumors 68030

    Big-TDI-Guy

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    #21
    Don't drop those screws and pins on that floor! ;)
     
  22. jimmy43, Jul 12, 2012
    Last edited: Jul 12, 2012

    jimmy43 thread starter macrumors member

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    #22
    Well it's all back together now! Amazingly, it booted up. We did some tests on it and it was really hard to tell if the temps are any lower because there are too many variables.. I wasn't too happy with that so I took it all apart again and re-applied the paste, this time I used the spread with your finger technique (with gloves ;)) and I think after that it's running maybe a few degrees cooler (when idling) which is good.

    I have some pictures of the first and second application I will post, as well I'll let you know how it goes after we load test it!

    thanks for all your help.
     
  23. SBF macrumors newbie

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    Apr 3, 2015
    #23
    I have exactly the same problem as jimmy43 and having followed the prescribed route Ihave not resolved the problem. Question is if the sensors on the GPU / heatsink are broken? They are glued on very firmly. any help is welcome as the mac works great with a SSD and it would be a shame not to resolve this heat problem.
     
  24. Coder74 macrumors newbie

    Coder74

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    Aug 30, 2017
    #24
    Arctic Silver has a 200 hour curing time. That is it will take 200 hours of heating and cooling cycles for you to see a change in the temperature. I am thinking of using Arctic MX-4 it is carbon based and has no curing time.
     
  25. cynics macrumors G3

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    Jan 8, 2012
    #25
    This thread is really old....

    Regardless I've had good luck with Thermal Grizzly Kryonaut. Its a bit expensive and probably not something I would use on PC but considering the inaccessible nature of the iMac I consider it worth it. It also checks all the easy to use boxes like not being electrically conductive, no curing, easy to apply, etc...

    I'm sure MX-4 is good too though.

    I used Kyronaut on a laptop (ThinkPad T420) when upgrading processors. While video transcoding I went from an i5 throttling due to temps to an i7 staying well within its limits. I was testing CPU performance but due to the throttling of the i5 it ended up being a test of TIM (stock vs Thermal Grizzly Kryonaut).
     

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