Reviving a 24" iMac (Early 2009, HD4850)

[ahurst]

So, back in 2014 my 2009 iMac's GPU started heating up worryingly (~95° C) under light use after years of reasonable temperatures. I took it into Apple, who concluded that it was the GPU and quoted me $500 for a fix. Since that was close to the cost of a new Mac and its Core 2 Duo was *much* slower than the Haswell i5s and i7s of the era, I upgraded to a new iMac and set my old one aside in its box.

Fast-forward 2 years, and I find an eBay service that reflows iMac GPUs for a very reasonable price. I send it off, get it back, and re-assemble the iMac only to find no difference in temperature. My dad, who I was gifting the old iMac to, has the idea to get out his thermal camera and see what's happening with the heat. Astonishingly, we learn that it's not the GPU that's the problem but the heatsink itself! Somehow, the heat pipes connecting the GPU to the heat fins had failed such that the heat wasn't actually getting carried over to the fan. Armed with this knowledge, we order a replacement heatsink off eBay, but it takes so long to arrive and I end up so busy with my degree that I never get around to installing it.

Fast forward to this afternoon: I've got some time off, and I decide to finally swap out the heatsink so I can have a Snow Leopard gaming machine for early Intel/late PPC games that won't run properly on later OSes. I tear the whole thing apart, repaste the CPU and southbridge, and get the GPU and heatsink all cleaned and ready to replace, until I notice to my horror that the new heatsink is slightly different than my old one, and thus won't *quite* fit on my GPU.

Above is Apple part 730-0573, which is a GPU heatsink for an A1255 Early 2009 24" iMac (ignore the metal brace, I just screwed that there so it didn't get lost). Below is Apple part 730-0545-A, which is *also* a GPU heatsink for an A1255 Early 2009 24" iMac. There's such little info on those part numbers that I can't tell whether the second one was for a different revision of the HD4850 or for the GT130 available in the same model.

Basically, I either have to:

a) Track down the correct heatsink somehow, or
b) Swap out the HD4850 with a different MXM GPU that'll work with the below heatsink.

For option A I'm having very little luck, with the only one I've found being on eBay UK and not shipping to Canada. For option B, I'd need to track down a GPU that would fit the working heatsink and also work with Snow Leopard. A GT130 would be the easiest choice, but it's quite a bit weaker than the HD4850 and would still set me back a hefty sum.

If anyone has any thoughts or advice, please let me know!

 

[sassemblyman]

First, let me tell you that these are still lovely machines worth it, in my opinion, to get running again. I have an early 2009 with a GT130, SSD, WiFi / BT upgrade, and while its not really economically feasible to keep running, it serves as a lovely computer in my workshop area, running Monterey 12.1 quite smoothly, and can boot all of the old school OS goodness.

Now, back to your issue. What exactly causes the misfit? Is it a memory chip hitting the heatsink? You could consider using a dremel to trim out the problem area, and just buy thermal pads for the chips. I did this for my 2010, as modification is required for many late 2009-2011 iMacs with swapped GPUs, which you can learn more about here: 2009-2011 iMac GPU Thread

Before you get too excited, the GPUs for those systems wont work in the early 2009 iMacs due to displayport vs TFT, the latter of which is used by the early 2009s. I am very much so hoping some members of the community release vbios flashes for these cards to allow for TFT displays in 2007-09 iMacs. They are my favorite. Right now the only functional solution with a metal GPU replacement is to turn the internal screen into essentially an external screen, and then run a displayport cable to it, as seen here: https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-29947555

 

[Ausdauersportler]

So, back in 2014 my 2009 iMac's GPU started heating up worryingly (~95° C) under light use after years of reasonable temperatures. I took it into Apple, who concluded that it was the GPU and quoted me $500 for a fix. Since that was close to the cost of a new Mac and its Core 2 Duo was *much* slower than the Haswell i5s and i7s of the era, I upgraded to a new iMac and set my old one aside in its box.

Fast-forward 2 years, and I find an eBay service that reflows iMac GPUs for a very reasonable price. I send it off, get it back, and re-assemble the iMac only to find no difference in temperature. My dad, who I was gifting the old iMac to, has the idea to get out his thermal camera and see what's happening with the heat. Astonishingly, we learn that it's not the GPU that's the problem but the heatsink itself! Somehow, the heat pipes connecting the GPU to the heat fins had failed such that the heat wasn't actually getting carried over to the fan. Armed with this knowledge, we order a replacement heatsink off eBay, but it takes so long to arrive and I end up so busy with my degree that I never get around to installing it.

Fast forward to this afternoon: I've got some time off, and I decide to finally swap out the heatsink so I can have a Snow Leopard gaming machine for early Intel/late PPC games that won't run properly on later OSes. I tear the whole thing apart, repaste the CPU and southbridge, and get the GPU and heatsink all cleaned and ready to replace, until I notice to my horror that the new heatsink is slightly different than my old one, and thus won't *quite* fit on my GPU.

Above is Apple part 730-0573, which is a GPU heatsink for an A1255 Early 2009 24" iMac (ignore the metal brace, I just screwed that there so it didn't get lost). Below is Apple part 730-0545-A, which is *also* a GPU heatsink for an A1255 Early 2009 24" iMac. There's such little info on those part numbers that I can't tell whether the second one was for a different revision of the HD4850 or for the GT130 available in the same model. View attachment 1960977

Basically, I either have to:

a) Track down the correct heatsink somehow, or
b) Swap out the HD4850 with a different MXM GPU that'll work with the below heatsink.

For option A I'm having very little luck, with the only one I've found being on eBay UK and not shipping to Canada. For option B, I'd need to track down a GPU that would fit the working heatsink and also work with Snow Leopard. A GT130 would be the easiest choice, but it's quite a bit weaker than the HD4850 and would still set me back a hefty sum.

If anyone has any thoughts or advice, please let me know!

You might take look here at my most recent post.

AMD Fire Pro M4000/M5100/W5170M/M6000 are now known to work properly in this iMac model!

 

[sassemblyman]

You might take look here at my most recent post.

AMD Fire Pro M4000/M5100/W5170M/M6000 are now known to work properly in this iMac model!

I am super stoked about this, as this is my favorite form factor of the aluminum iMacs. I have one now as upgraded as I can get it, but this opens up new possibilities. Sourcing a card now and hope to be able to post results when I have the time.

The issue I am having before putting this thing back together is that the WiFi upgrade, at least the BCM94360cd, when Bluetooth is plugged in, prevents the Mac from booting. Waiting until the apple logo comes up and the OS starts loading to plug the required usb connection to the existing BT socket on the MB results in a booted machine with BT and WiFi. I need to figure out how to nondestructively add a switch or some manual connection, perhaps through the ram door, to allow me to do so on the fly with the front panel and glass on.

 

[Ausdauersportler]

I am super stoked about this, as this is my favorite form factor of the aluminum iMacs. I have one now as upgraded as I can get it, but this opens up new possibilities. Sourcing a card now and hope to be able to post results when I have the time.

The issue I am having before putting this thing back together is that the WiFi upgrade, at least the BCM94360cd, when Bluetooth is plugged in, prevents the Mac from booting. Waiting until the apple logo comes up and the OS starts loading to plug the required usb connection to the existing BT socket on the MB results in a booted machine with BT and WiFi. I need to figure out how to nondestructively add a switch or some manual connection, perhaps through the ram door, to allow me to do so on the fly with the front panel and glass on.

Try to get such a M5100/M6000/W5170M card, I have tested no other and I am a little bit tired of assembling and disassembling the iMac again and again. The M6000 has the same GPU but a different form factor (MXM-B). All cards are relatively cheap to get.

In case you have a system with a working GT120/GT130 or better ATI 4850 GPU please use this tool and save the registry and upload it. Could help to make the brightness control better. You can use a PM in case you do not want to share this data in the public.

Thanks in advance!

P.S.: Will test a BCM94360CD myself. Need another adapter board…