I have an older laptop that was stored for a while. When I started using it again, it began registering random key presses from the built-in keyboard, so I disconnected the keyboard ribbon 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 disconnected the touchpad, mouse, backlight, and other peripherals, but the behavior continues in both Windows and Ubuntu. How can I determine what is generating the key presses, and is there a way to disable or stop them?
3 Answers
Since the problem happens in two different operating systems, this probably is not a Windows or Ubuntu software issue. The likely causes are a damaged keyboard connector, contamination or corrosion around the connector, or a fault in the motherboard's keyboard scanning circuit or embedded controller. Inspect the connector and nearby components closely for residue, bent contacts, or corrosion, including the underside of the board if possible. Testing in the BIOS or boot menu can help confirm that the input is occurring below the operating-system level.
For a temporary workaround, disable the internal keyboard device in the operating system if it still appears in Device Manager or the equivalent hardware list, then use the external keyboard. That may not work if the controller is generating input at firmware level, and it will not fix the underlying hardware problem. If the phantom input also appears in BIOS, motherboard repair or replacement is the realistic long-term solution.
Make sure the disconnected ribbon is fully isolated and cannot touch exposed contacts or nearby traces. If the connector and cable are definitely not involved, the fault is probably on the motherboard. The embedded controller may be seeing a stuck row or column in the keyboard matrix, which would explain why the symptoms remain across operating systems.
A clean visual inspection may not reveal an electrical fault. Moisture damage or a failed component in the keyboard matrix can still produce phantom presses even when the keyboard itself is unplugged.