The cause of the fault: the keyboard line is damaged or the contact is poor, the keyboard master IC program is lost or invalid, the IC matching crystal oscillator or matching capacitor is invalid, and the relevant circuit components are invalid;
Solution: Use the software exclusion method and the substitution method to check the relevant components in the following order;
1. Re-write the keyboard master IC definition program;
2. Replace the keyboard line;
3. Keyboard main control IC;
4. Other related components of the keyboard main control board.