I have an older laptop that was stored for some time. When I started using it again, the built-in keyboard began generating random key presses, so I disconnected its ribbon cable from the motherboard and switched to an external USB keyboard. That worked for a couple of months, but the phantom input has now returned even though the internal keyboard is still disconnected. I have also unplugged the touchpad, mouse, keyboard-backlight cable, and other peripherals, but the unwanted key presses continue in both Windows and Ubuntu. What hardware could still be generating this input, and how can I disable or troubleshoot it?
3 Answers
As a temporary workaround, try disabling the internal keyboard device in the operating system, if it still appears there, and use the external keyboard instead. That may stop input after boot, but it will not fix activity caused by a shorted controller and will not help in the BIOS. The permanent solution is usually motherboard-level repair or replacement.
With the keyboard and other input ribbons removed, the most likely remaining cause is on the motherboard itself: contamination, corrosion, or a short around the keyboard connector or embedded keyboard controller. A visual inspection may not reveal a high-resistance or intermittent short, especially on a laptop that was stored for a long time. Disconnect the battery and charger, inspect and clean the connector and nearby components with suitable electronics-grade isopropyl alcohol, and check for corrosion or damaged traces. If the fault remains, the motherboard or its keyboard controller may need repair or replacement.
Double-check that the USB keyboard is not the source by disconnecting it and booting with no keyboard attached at all. Since the behavior occurs in both Windows and Ubuntu, a software driver is unlikely; firmware or motherboard-level input is much more plausible. You can also enter the BIOS or a boot menu and see whether the phantom input occurs there.
If the keys activate before an operating system loads, that confirms the problem is below the OS level. At that point, reinstalling Windows or changing Linux settings will not solve it.
There may not be an obvious bridge between the connector pins. Residue or damage on the exposed contacts of the disconnected ribbon can also cause trouble if it is touching the board, so remove the cable completely or insulate it rather than leaving its contacts near the connector.