Lenovo Ideapad S340-15IWL Laptop Key stuck problem

Model : Lenovo Ideapad S340-15IWL Type 81N8
Board id: EL5C3 EL531 EL431 LA-H101P REV 1.0

Problem is "q" Key is stuck and appear repeadely without Keyboard. I flash BIOS from supported original lenovo website and BIOS and EC version are changed. But problem still exits. There is nothing (Capacitor, Diode, etc ... ) on Keyboard circuit line. All are directetly connect with EC. Need help.

Disconnect the keyboard while in the app (eg. Notepad) and check if "q" letter is still typed. If NOT, replace the keyboard. If SO, replace the EC.

I already tested with disconnect keyboard. When i replace EC, can i need to reprogram?

If you will use a brand new KBC chip (or a erased one), it should automatically program itself the first time you connect the power supply to the board.

I replaced EC with another EC from exectly same laptop ( same model and board id ). But problem still exit. "q" key is still stucked and appear repeadely without Keyboard.

Measure the voltages to ground on all pins of the keyboard connector while the machine is booted into the OS with the keyboard disconnected.

Pin 2,7,8,9,11,12,15,18 - 3.3V
Pin 13,14 - 3.2V
Pin 32 - 5V

All other pins have 0V.

cygron wrote:Pin 13 - 3.2V

And here the problem is. This pin should be 0V.

Lift the pin 39 of the KBC chip (or cut the copper trace connected to this pin). Then remeasure the voltage to ground on pin 13 of the keyboard connector while the machine is booted into the OS with the keyboard disconnected.

i cut the copper trace connected to this pin. the voltage to ground on pin 13 is still 3.2v but key struck is gone.

Everything points to a short circuit somewhere between the inner layers of the PCB laminate.

Also cut the copper trace connected to the pin 13 of the keyboard connector and remeasure the voltage to ground on this pin while the machine is booted into the OS with the keyboard disconnected. If you measured 0V on this pin, run a kynar wire between pin 13 of the keyboard connector and pin 39 of the KBC chip.

Cut the copper trace connected to the pin 13 of the keyboard connector and the voltage is 0V. I connect a kynar wire between pin 13 of the keyboard connector and pin 39 of the KBC chip. Now everything is fine. If you don't mind, i want to ask how do you know pin 13 of keyboard connector should be 0V.

cygron wrote:i want to ask how do you know pin 13 of keyboard connector should be 0V.

In the initial state (none of the keys are pressed) all KSI (Keyboard Scanning Input) pins of the KBC chip should be 3.3V and all KSO (Keyboard Scanning Output) pins should be 0V.

Thank you very much for your helping and teaching. Best regards.