If the characters out are not the right characters you typed when using the keyboard, here are some fixes:
First, clean the dust, dirt and foreign matter on your keyboard by turning this device upside down, and you can use a can of compressed air to blow some hard-to-clean dust out from the device.
In case you spill some drink or other liquid on the keyboard by mistakenly, turn the device upside down at once and let the liquid drain out, try to remove as much liquid as possible and then let your keyboard dry thoroughly.
Second, replacement method
If your keyboard is thoroughly clean but the problem continues to occur, try to connect another trouble-free keyboard to your computer. If it works normally, well then may be the primary keyboard is defective, you can take it to the repair center or exchange a new one if it is in the warranty time.
But if the second keyboard also could not function correctly, then the problem probably is in the port to which your keyboard connects to, so change the port.
To locate the problem you can also use a multimeter to test the flip-flop circuit on your keyboard and the circuit on the connecting port.
Third, sometimes on some computers, it is the wrong setting that leads to wrong characters are typed, for example you can adjust the settings from English (US) to English (UK) as bellow instructions:
Go to Start – Control Panel – Regional and Language, select the Language tab then press the details, select English (UK) in the dropdown tab then apply.
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