Need help troubleshooting system failure

It’s your graphics again they just replaced it with refurbished board as they had no other options those graphics cards were just a nightmare and there was No permanent fix without leaded solder that Apple were legally unable to use.

It’s just not worth putting any more money into it now, you are looking at a new computer.

 

This may be the only solution to get the machine semi-working: https://forums.macrumors.com/thread...fi-variable-fix.2037591/page-43#post-25325349

 

OP:

Looks like you've encountered "RadeonGate" (research that if you don't know what it is).

It's a GPU failure that requires a motherboard swap to "fix".
But... the fix is often only temporary, because the GPU on the new motherboard fails, too.

Apple used to have a free repair program for this but it's over for some time now.
They won't even do "paid repairs" on these anymore.

Best advice:
DON'T throw money at it (it's going down a hole).
Look for a replacement and put your money there instead.

 

As others have noted, this is almost certainly the dGPU issue - the replacement board Apple put in your system has the same fatal flaw as the one that originally failed. Avid Media Composer presumably activates the dGPU, which is why upon opening the App everything went nuts.

If you have an older version of OS X, you can use GFXcardStatus to force the system to use the iGPU only (at the expense of slower performance) - if you have a newer version, you can use the more permanent isoLinux method. Either way, you will lose the ability to use external displays.

Intentionally overheating the system and then immediately restarting it after a thermal shutdown will often allow the system to successfully boot, and in some cases may buy a short amount of time of proper function. A reball/reflow is another option, but one I discounted due to inconsistent outcomes, short warranties, and difficulty in finding a credible BGA repair specialist in my area.

My solution has been simple - kill the dGPU and never shut the system down. My 2011 with a failed GPU hasn't been restarted in months.

--- Post Merged, Nov 9, 2017 ---

I was under the impression that they only were legally unable to use it in parts of the EU and ultimately chose lead free for the entire design...?

Also, Apple could have always redesigned the board around the less-vulnerable 650M, or simply swapped out failed 2011s for less-vulnerable 650M-containing 2012s (it honestly may have been cheaper for Apple to do this from both a financial and a PR perspective...)