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Hi, I have 15" MacBook Pro Mid 2014. I’m having issues with ‘z’ key. When I first boot up my mac, on login screen I can see it is repeating keys before I hit the first key and it stops after I start typing any character on the keyboard. After I login to OS, ‘z’ key does not work at all. I was planning to replace the top case or the keyboard. However, I just tried to boot my mac after I disconnect keyboard ribbon cable. I realised even the keyboard is not connected, it repeats ‘z’. So looks like the issue is not the keyboard itself. What do you think the issue is?
IT sounds like you have corrosion on the logic board. You’ll need to fully remove the logic board to inspect it very carefully for signs of a liquid spill (staining) or visible corrosion. Follow this guide: MacBook Pro 15" Retina Display Mid 2014 Logic Board Replacement take some pictures of anything that looks off and post it here for us to see Adding images to an existing question. Use the pictures in the guide as well as the part its self to compare with your system.
