Caps Lock function cannot be turned off

You can make a Genius Bar appointment for hardware service using this link: Contact Apple for support and service - Apple Support

Get your Mac repaired and see how much will it cost: Mac Repair & Service - Apple Support 

Call Customer Support (800) MY–APPLE (800–692–7753) or on line /getsupport.apple.com/ 

or call AppleCare Support at 1-800-APLCARE (800-275-2273) 

You can try to login using a USB keyboard connected to the laptop. Even a PC keyboard can work.

You should also try a Safe boot - no password required and it may reset any cache(s) that have been corrupted.

Reboot the MacBook by hard pressing and holding the power button until the login options are displayed.

How to use safe mode on your Mac - Apple Support 

Does the same thing happen while in Safe mode?

You can exit safe mode by restarting your Mac normally, then reevaluate the problem.

Porcupine06 wrote:

Important: I had the battery unit (includes the keyboard) replaced half a year ago and it worked perfectly fine. It cannot be a hardware problem because otherwise it would type lower case letters (and the regular set of characters) when holding shift key - but it doesn’t!

Don't assume that is true.

Tom Gewecke wrote:

Porcupine06 wrote:

It cannot be a hardware problem

You really need to try an external keyboard to verify that.

FYI, unfortunately that may not have been an accurate test because a stuck key on the internal could still affect an external keyboard. However, it seems that was not the case here luckily for the OP and it provided useful information and options.

HWTech wrote:

Tom Gewecke wrote:

Porcupine06 wrote:

that may not have been an accurate test because a stuck key on the internal could still affect an external keyboard.

Could you elaborate on that? Is the idea that in some cases the external keyboard could also behave like the broken internal one, so it would appear to be a settings issue instead of a hardware problem?

Tom Gewecke wrote:

Could you elaborate on that? Is the idea that in some cases the external keyboard could also behave like the broken internal one, so it would appear to be a settings issue instead of a hardware problem?

If the built-in keyboard has a hardware issue where it is telling macOS one thing like a stuck key....lets say a stuck Shift key, then anything typed on the external keyboard will be considered as caps or as the upper symbol on multipurpose keys. Basically macOS will interpret the key presses of both keyboards, so if the built-in keyboard is spouting non-sense, you will still get nonsense from the external as well.

With the OP's Caps Lock issue, it was hard to say if it would interfere or not. I have seen some odd things with the Apple Caps Lock key on a few of my organization's Macs. However, if the external keyboard does work properly, then it does confirm a hardware issue with the laptop as is the case here. However, if the external keyboard also did not work, it would not necessarily tell us if it was a hardware or software issue.

Can you perhaps use the virtual keyboard to reset things?

Use the Keyboard Viewer on Mac - Apple Support

Ah yeah, my bad. Sorry.

• Try it with a USB keyboard.

• Give both of the Shift keys a good workout.

Porcupine06 wrote:

It cannot be a hardware problem

You really need to try an external keyboard to verify that.