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Yesterday my laptop's built-in keyboard started typing random keys, i.e. when I press Down Arrow, it would type 3, when I press it again, it would delete a character, pressing the Right Arrow would get me several lines down, then suddenly it would start working normally. Some keys worked properly, but a lot didn't.

I have Linux and Windows, dual boot, happened on both of them. Tried turning off the laptop and removing the battery, but the problem was still there afterwards.

When I plugged in an external USB keyboard and typed through it, it was working just fine, while at the same time, the builtin keyboard was having this weird behavior.

What could be causing this?


Edit

I haven't poured any liquids on the keyboard, but I had the laptop opened a month or so ago, to clean the dust from the fan, and to replace the CPU thermal paste, because it had started heating a lot even when idle.

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Did you by any chance pour any liquids into the laptop? Also, it could be a misaligned cable. I'd try disconnecting, cleaning a bit then reconnecting. Though this might involve getting the laptop completely apart... –  ppeterka Oct 17 '12 at 7:41
    
No. No liquids or anything. But I had had my laptop opened a month or so ago, to clean the dust, and replace the thermal paste of the CPU. –  sashoalm Oct 17 '12 at 7:44
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...or it might just be an engaged NumLock. Check for that! –  ppeterka Oct 17 '12 at 7:45
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The first thing I would do is disconnect the ribbon cable connecting the keyboard to the laptop and firmly reseat it. –  jmreicha Oct 17 '12 at 14:57
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2 Answers

Given that the problem appeared after the disassembly, I'd recommend disassembling again, and reseating the cable going to the keyboard. These ribbon cables can have several problems:

  • not inserted fully
  • misaligned, inserted with one side fully in, but the other side not
  • I've even seen a case when the contacts of the connector punched tiny holes into the ribbon cable, and this resulted in a wear out of the cables.

in a worst case scenario, you might have to get a replacement keyboard, or use it with an USB one.

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Click FN-button + F1 or F2 or F3...F12.

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I don't think recommending random actions (as Click FN-button + F1 or F2 or F3...F12.), which might result in turning the WiFi on and off, altering displaz settings and sound settings, or even sending the laptop to sleep/hibernate qualifies as halping one - especially without knowing the make and model of the laptop. –  ppeterka Oct 17 '12 at 7:48
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