65% Keyboard Tester

That’s normal. Makers assign that column differently: Del, Home, PgUp, PgDn and End are all common. The tester shows whatever each key sends under “Also detected”, so you can still confirm every key works.

Hold Fn and press the number row. F1 to F12 should then appear under “Also detected”. If the F-keys don’t register, the layer might be mapped differently in the keyboard’s software.

Fn is handled inside the keyboard. It switches the keyboard to another layer and is never sent to the computer, so no browser-based tester can see it. Test it by holding Fn and pressing a key on that layer, for example Fn + 1 for F1. The key it sends should light up here.

Rule out the setup first. Try another USB port or cable, charge or re-pair a wireless board, check any Windows/Mac mode switch, and try another computer. If a key still doesn’t register on a hot-swap board, swap its switch with one from a key you rarely use. If the fault moves with the switch, replace the switch. If it stays in place, the socket or circuit board is at fault. On soldered boards and laptops, clean under the keycap first. A key that stays dead usually means a repair or a new keyboard.

Chatter is when one press types a letter twice. It usually comes from a worn or dirty switch, or firmware that doesn’t filter contact bounce. The tester flags a key when a second press arrives less than 50 ms after the first. Even fast deliberate tapping leaves about 100 ms between presses, so anything quicker is the switch, not you. Holding a key down (auto-repeat) never counts as chatter, and you can change the threshold to 30 or 80 ms.

Hold several keys at once, such as A, S, D, F plus J, K, L. The “at once” count above the keyboard shows the highest number registered together. Many USB keyboards handle 6 keys plus modifiers (6KRO), while N-key rollover boards register every key. If a key you’re holding doesn’t light up, the keyboard is blocking that combination. If a key you didn’t press lights up, that’s ghosting.