Test the whole board first
Press every key in the tester above, watching the untested count fall. Do not stop at the key you already know about. The pattern of what else fails is the useful diagnostic, and it is invisible if you only test the one key that annoyed you.
Write down which keys never light. That list is what the rest of this page interprets.
Reading the pattern
| What failed | Most likely cause |
|---|---|
| One key, its neighbours fine | The switch itself, debris under it, or a bad solder joint. |
| A whole row or a whole column | A broken trace, a controller pin, or on a laptop the ribbon cable connector. |
| A scattered but fixed set | A matrix fault, or liquid damage that spread along the board. |
| Every key | Cable, port, driver, or a keyboard that lost power. Rarely the keys. |
| Keys work in the BIOS but not in the OS | Software: a driver, a remapping tool, or the wrong keyboard layout. |
| Keys work on another computer | The computer, not the keyboard. |
Cheap checks, in order
- Try a different USB port, ideally one directly on the machine rather than a hub or a monitor.
- Try the keyboard on another computer. Two minutes here saves an hour of software troubleshooting.
- Restart. A keyboard driver in a bad state is common enough to be worth ruling out early.
- Check the operating system keyboard layout. A US layout on a UK keyboard produces keys that type the wrong character, which people reasonably report as not working.
- Turn off Sticky Keys and Filter Keys if they have been enabled by accident.
- Unplug any remapping software, gaming software or macro utility and retest.
When the keyboard is worth repairing
A hot-swap mechanical keyboard with one dead key is a two-minute fix and a switch costs very little. A soldered mechanical keyboard is a soldering job but entirely doable.
A laptop keyboard with a single dead key is usually a whole-assembly replacement, because the keys share one membrane or one scissor plate. Before committing to that, a USB keyboard plugged into the laptop is a legitimate fix for a machine that mostly sits on a desk.
A cheap membrane keyboard with a whole dead row is generally not worth repairing. The failure is in a printed trace on a plastic sheet and the part costs as much as the keyboard.