Chosen Solution
This mac had a spill a long time ago. Was working fine for a while and then died. After Logic board was replaced, the Control key doesn’t work anymore. My question: With only one key not working, should I suspect the keyboard ribbon, or does ribbon related problems always affect more than one key? If it’s the keyboard, is there a chance to fix it, or would I need a new keyboard?
Often a single (or a small group) key(s) is a bad key switch contact do to liquid damage. If you’re lucky you maybe able to get it working by cleaning under the key that has a problem. Follow this YouTube vid: How To: Replace or Clean your MacBook, MacBook Pro, or MacBook Air Keyboard Keys. Once the key cap and scissor is removed you can try to clean things here. But be careful! You want to use distilled water and high grade Isopropyl alcohol on a cotton swab (Q-Tip) and just blot the areas with a slightly moistened swab as you don’t want the liquid to drip down deeper! If that fails you have a very big job here. The complete computer needs to be taken apart to get to the other side of the keyboard to then take it apart to clean from that end. Here’s a good vid on the amount of work it will take: Unibody Macbook Pro Keyboard Replacement - Liquid Spill Damage Repair by Rossmann Group. Louis still makes it look easy its not. I must warn you I find more often the parts are to far gone to make it worth all of the effort to take the upper case apart. It’s a lot easier just replacing the upper case assembly. Yes, its more expensive but a lot less time and it will work straight out. If you try cleaning the keyboard contacts you often need to go back in and that is not good.
