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changing vertical lines on screen // none in recovery mode

I executed a factory restore on this Imac and installed Catalina.

ISSUES — The problems I am having are shown in the attached image.

Lines on screen change in appearance
None appeared during the 15hr+ multi-pass format of the drive

ATTEMPTED — These are processes I have attempted.

Factory restore and clean OS install

Any information or suggestions appreciated as the Genius Bar is 2-3 weeks booked due to the current state of the world.

Stay safe all!

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投稿日: 2020年12月20日

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Sadly Apple won’t service your system as its too old ;-{ Vintage and obsolete products

As to your systems problem, your GPU boards VRAM chips have a problem!

Its a fair amount of work to take out iMac Intel 27インチ EMC 2374のAMD Radeon HD 4850ビデオカードの交換 in this case I don’t see baking as a solution as the VRAM chips don’t suffer the same way the GPU chip does. Morelikely you’ll need to replace it.

As to why In Recovery or Target Disk Mode the screen doesn’t have this issue. Your system has in fact two! Graphics engines. The discreet one (AMD Radeon) but a second one within the CPU! Intel graphics. When you first start up your system you are using the Intel graphics and then it switches over to the AMD GPU.

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iMac Intel 27インチ EMC 2309/2374

changing vertical lines on screen // none in recovery mode

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