National service hotline1. The fuse tube is blown
Under normal circumstances, a blown fuse tube indicates that there is a short circuit or overcurrent fault in the charger's internal circuit. This is because the charger works for a long time in the state of high voltage and high current, and the failure rate of internal components is high. In addition, the grid voltage fluctuation, surge will cause the charger current instantaneously increase and make the fuse.
Repair method: First of all, carefully check the components on the circuit board to see whether the surface of these components is burned or there is electrolyte overflow, smell - smell there is no difference. Then measure the resistance value of the power input, if less than 20OkΩ, it indicates that there is a local short circuit phenomenon at the back end, and then measure the positive and reverse resistance value of four rectifier diodes and the resistance value of two current limiting resistance, to see whether there is short circuit or burnt out; Later, we will measure whether the power filter capacitor can be charged and discharged normally, whether the switching power tube is broken down and damaged, and whether UC3842 and its surrounding components are broken down and burned out. It should be noted that due to the on-road measurement, the measurement results may be wrong or cause misjudgment. Therefore, the components can be welded down for measurement when necessary. If no, measure whether the input and output power cables are short-circuited. Generally speaking, in the fuse failure, rectifier diode, power filter capacitor, switching power tube, UC3842 are vulnerable parts, damage probability can reach more than 95%, to check these components, it is easy to troubleshoot.
2. There is no DC voltage output or the voltage output is unstable
If the fuse is in good condition, in idle condition with load. The reasons for this kind of failure are: overvoltage, overcurrent protection circuit open circuit, short circuit phenomenon; The chattering circuit is not working; The power load is too heavy, the rectifier diode in the high-frequency rectifier filter circuit is broken down, the filter capacitor leakage, etc.
Maintenance method: First, use a multimeter to measure whether each component of the high-frequency pulse transformer is damaged: After eliminating the breakdown of high frequency rectifier diode and load short circuit, the DC voltage of each output is measured. If the output is still low at this time, it is certain that the control circuit of the power supply is faulty. Later, use a multimeter to statically measure whether the rectifier diode and low voltage filter capacitor in the high frequency filter circuit are damaged. General fault can be removed. But pay attention to: output line break or open welding, virtual welding will also cause this fault, should pay attention to this situation in maintenance.
3. No DC voltage output, but the fuse is intact
This phenomenon indicates that the charger is not working, or after working into the protection state.
Maintenance method: First, it is necessary to determine whether the transformer control chip UC3842 of the charger is in working state or has been damaged. The specific method of judging is as follows: Test the voltage of pin 7 to ground of UC3842 with electricity. If pin 7 has normal voltage and pin 8 has +5∨ voltage, pin 1, 2, 4, 6 also has different voltage, then it indicates that the circuit has started and UC3842 is basically normal. If pin 7 is low and other pins have no voltage, the UC3842 is damaged. Very common damage is 7 foot to ground penetration, 6 and 7 foot to ground penetration and 1 and 7 foot to ground penetration. If these feet are not broken and the charger still cannot start normally, it means that the UC3842 is damaged and should be replaced directly. If it is judged that the chip is not broken, it is necessary to check whether the current limiting resistance of the gate of the switch is open welded, virtual welded or variable value, and whether the switching power tube itself is poor performance. In addition, the power output line break or poor contact will also cause this fault, so in the maintenance should also pay attention to.
4. The DC voltage output is too high
This fault is often caused by the voltage regulator sampling and voltage regulator control circuit abnormal, in the charger, DC output, sampling resistance, error sampling amplifier, optical coupler, power control chip together to form a closed control loop, any one of the problems will cause the voltage rise.
Maintenance method: Because the charger has overvoltage protection circuit, the output voltage is too high will first make the overvoltage protection circuit action. Therefore, in the event of such a failure, we can disconnect the overvoltage protection circuit, so that the voltage protection circuit does not work, and then measure the main voltage of the power supply at the moment of startup. If the measured value is more than 1V higher than the normal value, the reason for the high output voltage is indeed in the control loop. At this time, it is important to check whether the sampling resistance is variable or damaged, and whether the precision reference voltage source (TL431) or the optocoupler (PC817) has poor performance, deterioration or damage. The precise reference voltage source (TL431) is easy to be damaged. We can distinguish the precise voltage stabilizer by following method: connect the reference end (Ref) of TL431 with its Cathode, string 1OkΩ resistor, and connect 5∨ voltage. If there is 2.5V between Anode and cathode and still has 2.5∨ for a while, it is good tube, otherwise it is bad tube.
5. The DC voltage output is too low
According to maintenance experience, in addition to the voltage regulator control circuit will cause the output voltage is too low, there are the following reasons:
(1) The rectifier three-pole Ju and filter capacitor fail at the output voltage end, which can be judged by the substitution method.
(2) The performance of the switching power tube decreases, leading to the switch tube can not be normally switched on, so that the internal resistance of the power supply increases, and the load capacity decreases.
Electric vehicle charger
(3) The source pole of the switching power tube is usually connected with a resistance with small resistance but large power, which is used as the overcurrent protection detection resistance. The resistance value of the resistance - generally in 0.2 ~ O.8Ω. Such as the resistance change value or welding, poor contact will also cause the output voltage is too low.
(4) Bad high-frequency pulse transformer not only causes the output pressure drop, but also causes insufficient excitation of the switching power tube, thus repeatedly losing the switching tube.
(5) The high voltage DC filtering capacitor is poor, resulting in poor load capacity of the power supply.
(6) The output line of the power supply has poor contact and a fixed contact resistance, resulting in too low output voltage.
Maintenance method: First, use a multimeter to check whether the high voltage DC filter capacitor deteriorates, whether the capacity decreases, and whether it can be charged and discharged normally. If there are no above problems, then measure the current limiting resistance of the switching power tube electrode and the overcurrent protection of the source pole to measure whether the resistance is variable, metamorphic or welding, poor contact. If no, check again whether the iron core of the high-frequency transformer is intact. In addition, z may be output filter capacitance reduced, or open welding, virtual connection; Power supply output current limiting resistance change value or virtual connection; The power output line is virtual connected.
Trapped elements are not let go, should be carefully checked to ensure that nothing - loss.
6, the hot fan does not turn
The main reason for the fault is that the audion controlling the fan (generally 8550 or 8050) is damaged, or the fan itself is damaged or the wind blade is stuck by debris. But some chargers use intelligent heat dissipation, for the use of this way of heat dissipation charger, thermistor damage probability is very large.
Method: First of all, use a multimeter to measure whether the triode of the control fan is damaged, if the tube is not damaged, it may be the fan itself is damaged, you can pull the fan off the circuit board, in addition to a 12V direct current (pay attention to the positive and negative electrode), see whether the rotation, but also see if there is no foreign matter stuck. If you swing the fan wire several times, the fan will turn, it indicates that there is a broken wire inside the wire or the connector contact is poor. If not, the fan will fail. For the charger with intelligent heat dissipation, in addition to the above inspection, should also check whether the thermistor contact is bad or damaged, welding and so on. However, it should be noted that the thermistor is a negative temperature coefficient, which should be paid attention to when replacing it.
(7) The power grid voltage is too low. Although the charger can still output the rated charging voltage at low voltage, it can also make the output voltage too low when the grid voltage is below the very low voltage limit of the charger.