My Lenovo Legion Y540's built-in keyboard no longer responds to normal typing or NumLock, although several hardware shortcuts still work, including brightness adjustment with Fn+F5/F6, keyboard backlight control with Fn+Spacebar, and the lid logo light with Fn+L. The NumLock indicator usually stays lit but does not change when pressed, and the numpad is also unresponsive. At startup, the NumLock light comes on unusually early and remains on.
The keys do not feel stuck or physically damaged. The laptop runs Windows 11 with an Intel i7-9750H, 32 GB of RAM, and a GTX 1660 Ti. It was recently cleaned, and its swollen battery was replaced a few months ago. The repair shop mentioned that the swollen battery had damaged a support near the trackpad buttons, but they did not report any keyboard damage.
Restarting, reinstalling or rolling back the keyboard driver, disconnecting peripherals, unplugging the charger, and holding the power button to discharge the system have either failed or only helped temporarily. A Bluetooth keyboard and a USB keyboard both work normally. The built-in keyboard also does not respond in the BIOS, so this appears to be more than a Windows driver problem. What hardware issue should I investigate, and is there anything else I can test before replacing the keyboard?
2 Answers
The working USB keyboard confirms that the system itself can process keyboard input, while BIOS failure points toward the internal keyboard hardware or its connection. Open the bottom cover only if you are comfortable doing so, disconnect the battery, and reseat the keyboard ribbon cable carefully. Look for a partially lifted locking tab, bent contacts, creasing, or corrosion. If reseating it changes nothing, a replacement keyboard assembly is more likely than another driver reinstall.
Since the built-in keyboard does not work even in the BIOS, Windows drivers are very unlikely to be the cause. The fact that the Fn lighting and brightness controls still work suggests the laptop is receiving some signals from the embedded controller, but the main key matrix is not communicating correctly. The most likely causes are a loose or damaged keyboard ribbon cable, a damaged keyboard, or a fault in the keyboard controller on the motherboard. Given the previous swollen-battery damage and recent cleaning, I would have the keyboard connector and ribbon inspected first. If the cable and connector look good, replacing the keyboard is the next practical test.
I tried the full power-button discharge and checked the BIOS, but the built-in keyboard still does not respond there. A USB keyboard works normally, so I will have the internal cable and keyboard checked rather than continuing with Windows drivers.