Upgrade iMac late 2009 27" Hardware with Mid 2011 parts

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Hi all,

I am looking into upgrading my old iMac Late 2009 core i7 27-inch with 32 GB (1066 MHZ DDR3) RAM, OWC SSD as a startup disk + 2 TB HDD, running HighSierra.
The current logic board is having issues and needs replacement. The original graphic card (ATI Radeon HD 4850) won't run on Mojave or Catalina.
I have the following questions:

- Does somebody have any experience with replacing the late 2009 logic board with a logic board of an iMac Mid-2011 "Core i7" 3.4 27-inch? will it fit in
the late 2009 casing and are there be incompatibilities with other internal components such as: power supply, RAM memory but also physical
connectors?

- Could you possibly advise a graphic card that will run Mojave and up?
I have read about compatible graphic cards which do not have the Mac VBIOS running. As a result, no backlight control from the
keyboard.

Apologies for the very technical questions and thanks in advance for anyone 'support
 

Cory Cooper

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Hello and welcome.

That type of repair is not recommended, as internal components on iMacs are not user-serviceable, and can be easily damaged without the proper tools and experience.

That said, the logic board and other internal boards of those two models aren't compatible/interchangeable, due physical dimensions/port configurations and electrical design.

There isn't an upgrade you can install that would make the 2009 iMac hardware compatible with Mojave...you would need to purchase a newer iMac model.

I am not sure what you mean by Mac VBIOS - I have never head that term?

C
 
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Hello Cory and thanks for your warm welcome!

The complication of this repair is not a challenge for me. I have the right tools and experience as I have been upgrading this old beast several times through its 11 y of life. I came to realise that both logic boards are different which will pose a problem to fit in the casing let alone the electrical and connector compatibility aspects. I have dropped the idea of upgrading to a mid 2011 of even 2010. I will replace the faulty late 2009 logic board by another second hand late 2009 one.

W.r.t the graphic card I read several threads and forums where some graphic cards are compatible with the metal API and therefore can enable the old late 2009 to upgrade to Mojave or Catalina. One of the caveats is that without a MAC firmware (so called VBIOS) on the card, there will be lcd backlight issues and other stuff. Some claim "hoorah it works like a charm" others are still reporting struggles and indicate that re-flashing the graphic card to make it work on Mac is a challenging thing to do. So I am still trying to understand what to do before I get myself into a potential nightmare.
 

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