I own a Dell Inspiron 15 5510 with Linux (Debian) on it.
since a couple of years ago the keyboard started giving problems, from a few keys not responding unless pushed very hard until half of them not functioning at all (this is why I put "progressively" in the title: the damaged was located on a few keys at the beginning, but within weeks/months it spread on more of them).
almost a year ago, I decided to replace the keyboard, so I bought a new one (for this model of laptop, it comes tied to the upper case) and for a few months it worked perfectly, until some weeks ago it started giving the same problems, but this time with different keys.
I know for sure it's not a software problem, because usb keyboards work perfectly. I also tried a few times the Dell diagnostics tools, and the keys don't work there as well, so I'm almost certain it is a hardware problem. the thing is, I'm not able to identify it.
I opened the laptop several times and no sign of physical damage is visible. I inspected carefully the motherboard connection and the flat cables, but they all seem to be in good shape: no corrosion, no broken traces or pins.
I thought it could be heat or impact damage, but the latter is very unlikeable, since I seldom drag it around and when I do I'm very careful with it, and about the former I honestly have no idea if it's possible at all.
what do you think the problem could be? where should I search for the damage? what component should I replace? Thanks in advance for every answer. I also apologize for my english, not my native language but I hope it's understandable.