On / off key, a heating lamp bright, in the lowest thermal state is normal, by adjusting the "a" and "+" key regulatory prompting sound, but the thermal constant, screen display is also unchanged: according to the "heating, insulation / timing" key to regulate normal. In the heat preserving state, according to the "a" and "+" key preserving temperature does not change. The screen is equally unchanged. Analysis of the abnormal situation of the normal and the screen from the part of the function.
Faults should be in the key and the screen display circuit. The circuit takes 8 bit shift register (74HCl64N) as the core, and the correlation key, transistor and resistive element are all good.. Judge 74HCl64N damage. After the replacement of the register, all the functions and the screen are recovered and the fault is eliminated.