After the refrigerator frost can not start the normal cooling failure:

    Case Description: The refrigerator is a Valin bcd-320w intercooled refrigerator, refrigerator op amp lm324 pin bad contact, resulting in the refrigerator after the end of the defrost can sometimes start cooling, and sometimes can not boot the situation; Case refrigerator repair case, be aware of multi-door refrigerator microcomputer thermostat control circuit analysis method steps.

    Analysis and overhaul: This Valin bcd-320w cold refrigerator used less than two years, the recent emergence of defrost after the end, sometimes can not automatically boot the situation. Home inspection, the refrigerator users placed in the kitchen to use.

    The refrigerator for the four-door cold, the upper room for the refrigerator. Built-in 23 liters of ice temperature preservation room, the middle two rooms for the freezer. With quick-frozen function. The lower room is the fruit and vegetable room. The temperature can be switched between cooling and cooling. To troubleshoot this problem. Must first understand and master its working principle.
    Refrigerator microcomputer thermostat by the transformer rectifier, temperature detection and operation control of three parts.

    1. refrigerator microcomputer thermostat transformer rectifier part

    The mains 220v by the transformer b1 step down to 9v, d01 a d04 composed of full-wave rectifier circuit, the b1 from the 9v AC rectifier. C01 a c04 is the filter capacitor, and then by the three-terminal regulator 7805. Will be 9v regulator into 5v output, the supply chip mc68hc05 (hereinafter referred to as icd) and lm324 operator and its surrounding components. Rectified DC voltage is also used for three relays jl, j2, j3 and its supporting control components bg2 a bg4 and d06 a d08.

    2. Refrigerator microcomputer thermostat temperature detection part

    Control circuit board slot cn2 5,7,8 feet were connected to the freezing room temperature head, cold room temperature head and defrosting temperature head and other three signal components, three thermistor sub-ij detection freezer , The temperature of the refrigerating compartment and the evaporator, the impedance of the thermistor changes when the three temperatures change. Correspondingly icl signal input pin level changes. The thermistor converts the temperature change of the refrigerator into a level signal. And passes this signal to the control element. R01 a r04, c08 and c11, respectively, from the freezer compartment and refrigerated room changes in the high and low frequency clutter filter to reduce interference and improve signal strength. Cn2 in the 1-4 feet were connected to the two variable resistors w2l, w22. Used to control the indoor temperature of the cold onion and freezer compartment. Two variable resistors are input to the icl 22 feet and 21 feet, as the sink 1 for the freezer compartment, the freezing chamber temperature signal input pin 24,23 signal comparison benchmark. So as to determine the opening and closing of the refrigerator or the damper opening and closing.

    3. Refrigerator microcomputer thermostat running control part; refrigerator running state. Completely controlled by icl, its working principle is as follows.

    The refrigerator ambient temperature is set at 32 ° C. The temperature of the freezer compartment and the refrigerating compartment are set by the temperature fine adjustment control elements w21 and w22 respectively. When the corresponding temperature of the freezer compartment is "weak", "medium" and "strong", the freezing compartment temperature is set to -20 ° C to -18 ° C, -22 ° C to -20 ° C, and -22 ° C to -24 ° C. When the refrigerator temperature fine-tuning knob corresponding to the waste to "weak", "medium", "strong", set the refrigerator temperature of 7 ℃ ~ 9 ℃, 5 ℃ ~ 7 ℃, 3 ℃ ~ 5 ℃. Icl as a judgment condition. The two temperature sensors sent to the signal to determine and determine the action.

    When the temperature of the freezer compartment does not meet the requirements. If the freezer door is closed at this time. Icl connected relay j1 and j2 (after turning on jl, the throttle motor began to turn, when the damper open in place, the damper position switch connected to the icl signal, the chip received the signal, close the door, the door motor to stop the rotation, Complete open the throttle action), so that the refrigerator electric damper open, compressor and freezer fan normal operation.