The following points have been made: (original experience of Hou Sen) 1. When the motherboard and panel are clean; Continue to check below; 2. The first situation is normal; 220V AC, 300v DC, 22v or 20V (some models), voltage regulator 18V(+- error must be controlled within 1V), voltage regulator 12V for some models, and voltage regulator 5V(+- error must be controlled within 1V). 3. The heating coil is normal, and the parallel coil is 0.27UF or 0.3 uf or O.33UF, several large resistors and diodes, 4. The IGBT is driven to drive the pair of tubes (the 8050 8550 IGBT is replaced together when it is replaced), which are connected in parallel with the IGBT E-pole G-pole 18V voltage regulator. In general, there is 0.8 ~ 65438 between IGBT+ and-. 5. Current transformer detection; Whether there is; 0.025 volt AC voltage, 6. Is NTC (furnace surface and IGBT) normal? Is there a pot with +5V (room temperature 25℃NTC should be between 46 and 58K, and some induction cookers can't detect NTC at 100K? Fault analysis of alarm sound: There are many reasons for this fault, including synchronization circuit, surge protection circuit, boiler inspection circuit, drive circuit, IGBT high voltage protection circuit and PWM signal circuit. The following is the maintenance method. (1) Steps for fault inspection of synchronous circuit: ① Measure the working voltages of pin 8 and pin 9 of U 1-LM R239 with multimeter (pin 8 is 1.75V and pin 9 is 1.9V). If the voltage is abnormal, please check R 18 and R66. If the voltages of the above two pins are normal, let's measure whether the voltage of the 14 pin of U 1-LM 339 is too high, and the voltage value is1.23v. If it is low, it means that U 1 has been damaged (the fault of PWM signal circuit is excluded here). ② If the voltage is high, please ground pin 9 with a wire, and then measure whether the voltage at pin 14 is low. If it is still at high level, it means that U 1-LM 339 has been damaged, and it has been replaced with U20 1-LM 339 of the same model and specification. The machine is normal after power-on, and the fault is eliminated. (2) Fault analysis of surge protection circuit: Surge protection is generally a violent pulse with only a few millionths of a second in the power supply. In order to protect the IGBT from damage, the protection circuit will output a low level to stop the IGBT from working, and the circuit will automatically return to normal after the surge. Inspection steps: ① firstly, measure whether the 13 pin of U2-LM339 is at high level. If it is high, it means that the surge protection circuit does not work. If it is low, it means that the surge protection circuit has acted (this pin is connected with the output pin of IGBT high-voltage protection circuit, and here is the analysis of troubleshooting of IGBT high-voltage protection circuit). Let's measure whether the voltage at pin 1 1 of U2 is 3V, and whether the voltage at pin 1 1 is lower than that at pin 10 (the voltage at pin10 is 2.51. If yes, it means that U2-LM 339 has been damaged, and the fault can be solved after replacement. If the voltage of pin 6 and pin 7 of U202 is abnormal, please check whether R5, C22, R6, D206, D207, C206, C207, C2 17, R2 18 and R223 are normal, and replace the abnormal components to eliminate the fault. ② If the voltage at pin 14 of U2 is only 0.3V, and the voltage at pin 1/kloc-0 is greater than that at pin 10, we will measure whether the voltage at pin1of the main IC is low. If so, the main IC has been damaged. After replacing a new integrated circuit, the fault can be eliminated. (3) Inspection steps of the circuit fault of the pot: ① When the pot can't be detected, first we measure whether the 19 pin of the main IC has 5V voltage. If the voltage is 0V, it means that the main IC has been damaged, and the fault can be eliminated after replacement. If the voltage is normal, please measure whether the second pin of U2-LM 339 has a voltage of 0.8V. If not, please check according to the method in step 2. If yes, please check whether Q202 and R42 are normal. Replace the damaged parts, and the fault can be eliminated. If the above components are not damaged, we will judge whether it is the main IC or U2-LM 339. Connect pin 4 of U2 to 5V power supply with wires. If the measured voltage is low, the main IC is broken. If the measured voltage is still high, it means that U2- LM339 is damaged. Replace the above-mentioned damaged parts, and the power-on debugging is normal. Troubleshooting. ② If the voltage at pin 2 of U2 is measured to be low before the pin 4 of U2 is shorted in the previous step, then we will measure whether the voltage at pin 4 and pin 5 of U2 is normal (the voltage at pin 4 is low and the voltage at pin 5 is 3V). If the voltage is abnormal, it is necessary to cut off the power supply, check whether the resistance values of R2 18 and R2 17 are normal, and replace the abnormal components. If the measured voltage is normal, the output of pin 2 is still low, indicating that U2 has been damaged. Replace it with LM339 of the same model, and the power-on tester is normal. Troubleshooting. (4) Fault inspection steps of the drive circuit: ① First, remove the coil disc, power on and measure whether the pin 2 of U 1 is high, and then measure the voltage of pin 5 and pin 7, which are the reference voltages of two comparators on the drive circuit, and have a fixed value (pin 5 is 1.7V, and pin 7 is about 0.4V higher than pin 5), and send them to the front. If the voltage of these two pins is abnormal, please check whether there is any problem with R253, R252 and Z203, replace the faulty components and debug them normally, so as to eliminate the fault. ② (Note: the coil disc must be removed in this step, otherwise the IGBT will be burned). If the voltage of pin 5 and pin 7 of U 1 is normal, turn on pin 6 of U 1 with 5V power supply, and measure whether the voltage of pin 6 and pin 2 of U 1 is low with multimeter. If one of these two pins is high, it means that U 1 is damaged, and it is faulty to replace it with a new LM339. (3) If the output voltages of these two pins are normal and the fault has not been eliminated, we should check Q 1, Q2, R234, R235, R237, R238, R7, R8, Z 1, D2 12, and remove the defective components and replace them with the same ones. (V) Fault analysis of IGBT high-voltage protection circuit: When the voltage of IGBT C electrode is higher than 1 135V, the protection circuit operates. At this time, the IGBT output power supply will be turned off. Detection steps: ① First, in order to judge whether the fault is caused by IGBT high-voltage protection circuit, we first measure whether the voltage at pin 14 of U2 is high level (this pin is connected with the output pin of surge protection circuit, here is the troubleshooting analysis of surge protection circuit). If so, the protection circuit is not working. If it is low, it means that the protection circuit has acted. We need to measure the voltage between pin 8 and pin 9 of U2 (pin 8 is 0.49V and pin 9 is 3.85V). If the voltage of these two pins is normal and the output of 14 pin is low, we can determine that U2-LM 339 is damaged. The fault can be eliminated after replacement. ② If the voltages of the 4th and 5th pins are abnormal, check R220, R22 1, C225, R24 1 and R240, and replace the damaged components. Power-on debugging is normal, troubleshooting. ③ If the high level of pin 14 of U2 is only 0.3V, and the voltage of pin 9 is greater than that of pin 8, we will measure whether the voltage of pin 1 of the main IC is low. If so, the main IC has been damaged. After replacing a new integrated circuit, the fault can be eliminated. Fault analysis of PWM signal circuit: if PWM signal is not output, IGBT will not work because there is no driving signal, and boiler detection circuit will give an alarm because it cannot detect the correct pulse signal. Inspection steps: Measure the voltage of the main IC 13 pin in standby state, and the normal value is 2.25V (effective value). If the voltage value is abnormal, please check R2 1 1, R2 12, R2 13, EC 12 and C208.