MacBook – Liquid keyboard damage on MB Air – password keys don’t work even with USB keyboard

keyboards are 2 layers of plastic film with tiny electric contact, separated by a third layer of plastic film with holes on the spot of every single key. when you press a key, the top and bottom plastic are pressed against one another inside the hole of the middle layer, and the electronic signal going from the top to the bottom layer tells your computer that the key is pressed.

problem is: separation is the same as an average good quality book paper sheet, or maybe the same as the aluminum sheet that makes a soda or beer can. also, the electricity that goes trough your keyboard is extremely tiny, and sensors are VERRY sensible, so your air battery can lasts longer. So even if you have a single hair touching those circuits, your keyboard would "break" the same way it breaks when you spill coffee or whatever liquid; even after the liquid dries, the coffee and the sugar are probably still there "pressing" your alt key.

solution: (this will probably void any warranty) open your computer carefully, remove the keyboard, dismantle all keys one by one, separate the plastic layers with surgical precision so you don't cause any ruptures to the electric "wires", then wash everything with a lot of water and very little mild soap, take extra care to remove ALL the soap, leave everything to dry in the sun (you know electronic components don't like humidity, right?) assemble everything together with "just-washed" oil free hands (don't touch the inner part of the sensors now). Doing all this, if you have any luck your keyboard might work 100% again... or maybe you might make it stop working entirely, who knows? =)

if you have some money, then backup you computer, go to the applestore and tell them you want to buy a new keyboard, because you broke the current one. they shall give you a brand new (refurbished?) one, and charge you only the new keyboard. or they might give the same one back to you, who knows? haha.

I'm not surprised you may be experiencing this issue with Apple Software. Basically the Command-. keyboard shortcut has been used by Mac OS for decades as a universal "halt operations" keyboard shortcut.

In a sense it works in a similar way to the ESC key. So I am thinking this is why you are experiencing problems with this keyboard shortcut. It used to be that software developers had to respect this Command-. keyboard shortcut for any software they developed for the Mac platform, but this is no longer the case, hence why your keyboard shortcut may be working with some software but not others. You may want to read the Keyboard Shortcuts page in the macOS Human Interface Guidelines.

Extra Info

Apple first introduced the Command key in 1980 with the Apple III computer.

The purpose of the Command key was to allow users to enter keyboard commands in applications and within the operating system. The Macintosh Human Interface Guidelines have always recommended that developers use the Command key (and not the Control or Option keys) for this purpose.

A small set of keyboard commands (such as cut and paste, open and save) are standard across all applications. If an application needs more shortcuts than can be obtained with the twenty-six letters of the English alphabet, double modifiers such as Command+Option are used.

The Macintosh keyboard's other unusual modifier key, the Option key, serves as a modifier both for entering keyboard shortcuts and for typing text — it is used to enter foreign characters, typographical symbols, and other special characters.

As mentioned previously, the Command-. shortcut was once a universal recommended shortcut, but this is no longer reserved by macOS. In fact, Table 67-3 of the macOS Human Interface Guidelines now only lists one keyboard shortcut with a period (.) in it. This is the Control-Option-Command-. keyboard shortcut for increasing screen contrast. You can read more about this in Accessibility Programming Guide for OS X.