Screen distorted but external ok, GPU issue?

Hi guys,

I know this model has issues with the GPU and I have had it fixed by reflowing the GPU some years ago. But I think this may be different.

It has a perfectly straight rectangle taking up around 20% of the bottom of the screen which is mostly showing an equal color shade of white, black, grey, sometimes with some colors faded into it from what it should show on that part of the screen.

When I connect to my 24 inch Apple LED Cinema Display or Airplay (to my TV), all is fine. So external video is working ok via display port, (dual video also (laptop screen is still distorted)).

Here’s my question for troubleshooting on what I see on “Overview and Display” in “About this Mac”:

1. Running laptop by itself, it will only show Intel HD Graphics 3000 288 MB

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1. Connected to the Apple LED Cinema Display 24 inch, it will show both GPU’s
   • AMD Radeon HD 6490M 256 MB
   • Intel HD Graphics 3000 288 MB

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Things done so far, beside PRAM etc is opening the laptop and cleaning and reconnecting battery, display cable, harddrive. When I took out and reset RAM module, one died…. :-(

My take this is not again a GPU issue, or is it?