How to detect the problem of air conditioning circuit board?

　　The invention relates to a maintenance method of a power supply circuit of an air conditioning circuit board:

　　The fault characteristic of the power supply circuit of the air conditioning circuit board is that the safety tube is intact and burns out as soon as it is opened.

　　For the former fault, the AC block of the multimeter can be used to measure whether the primary and secondary voltages of the transformer are 220V and 10-13V, and then the DC block of the multimeter can be used to measure whether 7812 and 7805 have + 9-12V and + 5V voltages. In order to distinguish the fault location.

　　For the latter, it indicates that there is a short circuit in the circuit, and the short circuit position of the circuit is determined by detecting the resistance value of the multimeter ohmic block.

　　At the same time, the split method can also be used for inspection, for example, by disconnecting the transformer winding once and electrifying the tester. If the safety tube is also burned, it means that the burnout of the safety tube is due to the short circuit of the varistor or ceramic chip capacitor, otherwise it is due to the short circuit of the transformer or rectifier tube.

　　Inspection and repair method of temperature sensing circuit of air conditioning circuit board:

　　Thermistor is a kind of thermistor with negative temperature coefficient, that is, the higher the temperature, the smaller the resistance, the lower the temperature, the greater the resistance.

　　The resistance at 25 degrees is about 5-20K Ω (depending on the model).

　　Therefore, the resistance of the multimeter ohmic block can be measured to judge whether it is good or bad.

　　If the measured resistance is infinite or very small, the thermistor is damaged.

　　Circuit maintenance methods of air conditioning circuit board relays:

　　First of all, the difference is that the set success rate drive module is damaged or the relay is damaged.

　　If the buzzer rings after starting and pressing the remote control, but the whole machine does not work, the set success rate drive module is generally damaged.

　　If only part of the function is abnormal after startup, the relay may be damaged.

　　At this time, you can continue to monitor whether the relay absorbs sound, to determine whether the relay is burnt out or contact adhesion, and there is no sound absorption when the relay coil burns out.

　　The relay can also use the multimeter ohmic block to judge whether it is good or bad, disconnect the power supply, first measure the coil resistance value, the normal resistance value is several hundred ohms, if infinity or zero, the relay is damaged; then measure the contact, if the resistance value is zero, it means contact adhesion.

　　Maintenance method of air conditioning circuit board receiving circuit:

　　When the power is turned on, the DC block of the multimeter is used to measure the ground voltage of the power terminal and the receiver signal terminal.

　　The normal value should be + 5V voltage of power pole and + 2.5V voltage of signal pole.

　　Otherwise, it will not be normal.

　　Common faults include receiver head damage or capacitor failure.

　　Air conditioning circuit board reset circuit maintenance method:

　　The reset voltage is a delayed rise voltage, which can be observed through the DC voltage range of the multimeter.

　　If the observation is not clear, it can also be detected by the oscilloscope.

　　When detected by an oscilloscope, baseline jitter may occur and then become high.

　　This is the start-up process of resetting the voltage.

　　If you cant see the jitter of the baseline, there is something wrong with the reset circuit.

　　Maintenance method of crystal oscillator circuit of air conditioning circuit board:

　　When powered on, the multimeter is usually used to measure the double-needle voltage of the quartz transistor is about + 2.2V.

　　If it is less than 1.5V, the circuit will stop vibrating.

　　Elsewhere, it can also be judged by removing the quartz vibrating tube and using the multimeter ohmic block.

　　When measuring a good quartz vibrating tube with a multimeter, it should be open.

　　If a short circuit is found, the crystal will be damaged.

　　For the open circuit fault (wire break or electric shock crack), the multimeter can not be judged, and an alternative method can be used to check it.

　　Inspection and repair methods of air conditioning circuit board CPU chip:

　　Because the necessary conditions for the normal operation of the air conditioning CPU are: power supply voltage + 5V, reset voltage, clock pulse signal, these three conditions are indispensable, otherwise the CPU can not work properly.

　　Therefore, the multimeter can be used to detect the voltage in its working state.

　　If the voltage value is normal and the whole machine does not work, the damage of the CPU chip can be judged.