Chosen Solution
The left and down arrows on my keyboard aren’t working, but all other keys are fine. I removed the key caps and cleaned the interior parts, but that didn’t help. Pressing on the rubber key cup nipple doesn’t do anything. As far as I understand, that means that the issue is in the keyboard’s circuitry or other finicky parts, and not the key itself. What other parts could cause this issue? Would buying replacement keys help? Is there any way to fix it without a complete teardown of the upper case? Thanks!
Keyboard signals go through the trackpad plus a cable connecting trackpad to logic board. The only way to know where is the fault, is changing other parts, considering logic board can’t be ruled out unless you replaced all other parts with known good ones. Unfortunately there’s no other road than try and error. The cheapest and least troublesome would be try first the cable, then trackpad and finally the keyboard. The fastest replacing the full topcase.
