Sorry for the delay. I haven’t been on here in a while. For anyone interested, I have not been able to upgrade the OS in my machine. It appears there is a problem with having a newer graphics card in the older machine that causes some kind of conflict when upgrading.

Wow. What a difference. I actually have wifi now instead of almost no signal or no signal at all when I should have it. Do yourself a favor and get a bunch of Dixie cups and some sheets of paper to place them on. Number what step you are on on the paper. If there are multiple screws, arrange the cups in the positions of the screws so there will be no mixing them up. Also, take your time.

By the way, I can see why I didn’t have wifi before. One of the four connectors on the antenna was disconnected from the main part. When I removed the old antennae, the metal connector stayed on the phone.

I don’t see why that wouldn’t work. Read all the notes above before trying…

For anyone checking here about doing this upgrade, I have an update. I upgraded the GPU in my late-2009 27” iMac (see posts above for details) and have been happy with it. I am running El Capitan on it.

I recently tried upgrading to High Sierra and have not been able to do that. After trying to upgrade and then having to roll back to a backup, I tried a clean install on a blank partition and it still does not work. The problem appears to have something to do with the graphics driver. I am wondering if it has to do with the upgraded GPU. Just something to look out for. I have basically given up on upgrading the OS and I guess I will just stick with El Cap until the machine dies.

I do not believe that is possible.

If you can find a 6770M or 6970M that was pulled from a 2011 model iMac, I would bet that would work just fine. As mentioned above, you can definitely not just pick up any random 6970 (or other) GPU as it will not have the Mac firmware on it.

If you see my post above, I got a 2011 iMac 6770M GPU off of eBay and was able to put it in my 2009 iMac and it is still running great. Actually it runs a lot cooler than it used to.

You can only use a card from another Mac. Those cards have Mac-specific firmware on them that is NOT there on a generic graphics card.

Sorry, I didn’t see you questions. I have not checked here in a while. But, in case someone else has the same quesitons.

It has been a while, but I believe I went right to moving the card back to the heat sink it came with and then carefully reinstalled it. I believe the problem was just that it was not pushed in all the way and seated correctly. In theory, I don't see why the card moved to the other heat sink should not work. The cards are the same size with the mounting holes in the exact same place. There didn’t appear to be any difference in how the card sat on the heat sink.

Unless you are really adventurous, you should only swap out the processor in a Mac with one that was originally offered for that Mac model. So for your Core 2 Duo late 2009 iMac, I would only try one of these (preferably the faster one if you can find it of course):

3.06 GHz Core 2 Duo (E7600)

3.33 GHz Core 2 Duo (E8600)

Update! I guess I didn't have the card seated properly, because I took it out and re-plugged it in and now it is fine. In the process of playing with it, I put the card back on it's original heatsink since it was smaller and fit in the machine. I should have just left it to begin with...

Secondly, I WAS able to plug in an external monitor and start it up with the LCD monitor completely removed. That's good to know in the future. So, my late-2009 27" iMac now has a Radeon HD 6770M 512MB GPU in it that was pulled from a 2011 model. I can swear that the machine is running much cooler now. The new GPU must run cooler or all the dust I vacuumed out was really blocking all the air flow.