09-28-2018 07:21 PM
The problem happened unexpectedly, i.e., I didn't install any software, didn't update the BIOS, didn't change the hardware. Just one morning after the laptop booted as usual (in Linux), the problem appeared and keeps on appearing every morning ever since.
The problem: each key on the column "9-o-l-." when pressed started to activate (also) another key on the keyboard: "9" activates F11, "o" increases the audio volume, "l" mutes the audio speaker, and "." mutes the microphone. This is even visible on the keyboard LEDs "Speaker muted" and "Microphone muted."
The problem appears consistently in both Windows and Linux, and even before any OS boots (on the BIOS/Setup screen). However, after the laptop works for about an hour, the problem disapears (i.e., the keys don't activate other keys) and it does not appear until the next time I boot on the next day. I ran the keyboard tests on Windows and they passed.
Strangely enough, Shift +(problematic key) works correctly, i.e., gives the uppercase character of the corresponding key. However, Alt+(problematic key) gives the same problem as without Alt.
The following workaround works: I disable (in Linux) the shortcuts for the affected audio controls, so when "o" or "l" is pressed, the expected character "o" or "l" gets properly typed and is shown. Key "." cannot be deactivated as shortcut, but it both mutes the speaker and also correctly types "." (so annoying, but workable). Thus, it appears that when key "o" is pressed, it activates both the character "o" and the speaker mute. Because of some reason, the speaker mute gets handled with priority, so the character "o" is not shown. But by disabling the speaker mute in the Linux settings, the character "o" gets typed and is shown on the screen. Similarly for key "l".
Since the problem disappears after the laptop works for about 1h, alhough I am not working on it during this time, so I don't type on the keyboard (it just does a backup to external drive), I thought that it's temperatura related. So I tried to raise the temperature from the start by running computationally intensive tasks (=playing a video). The laptop heats up, but the problem persists. One bracket: the problem appeared after a week during which the laptop worked intensively and it's temperature was systemally higher, so it may have overheated during this time. But after the problem appeared, I put the laptop on an external pad with fans, reduced the CPU performance to Balanced in the BIOS, and make sure that it doesn't get very heated while working (=reduced its workload).
Connecting an external USB keyboard works correctly.
What I did so far: I removed the keyboard and cleaned with cotton and alcohol both the male and female parts (plug and socket) of the connector at the end of the cable which connects the keyboard to the system board. I also scratched the connector pins with a pin and with a screwdriver in order to remove possible corrosion/rust or other small particles. I disconnected and connected the cable multiple time. I also pressed the keyboard cable at various places to see if it is a bad wire and at the same time pressed the problematic keys.
Any advice what to do? Does this look like a solely keyboard issue, so replacing the keyboard will be enough, or a motherboard replacement may be necessary?