Hello, I am experiencing a strange issue with the Kyocera TA356ci. About a month and a half ago, the operation panel keyboard stopped responding, except for the power-saving button. The LCD and touch panel remained fine and worked normally. I replaced the entire operation panel, and everything seemed to be fine, but after a month, the issue recurred. I thought maybe it was because the newly changed panel was already used, so I installed another new one, and that got the machine back to work. Not even a week passed, and once again, the keyboard doesn't work. The machine has the latest firmware installed, and I've checked all voltages connected to the operation panel board; they seem to be as described in the service manual. None of the buttons are stuck. I'm running out of ideas about what could be causing this malfunction - the third time in a row. I will be grateful for any hints.