1. Blown fuse tube

In general, a blown fuse tube indicates a short circuit or overcurrent fault in the internal rotation of the charger. This is due to the charger working for a long time in a state of high voltage and high current, and the internal device failure rate is higher. In addition, fluctuations in grid voltage surges can cause an instantaneous increase in current within the charger and cause the fuse to blow.

Maintenance method: First of all, carefully check the components of the circuit board, see whether the appearance of these components are burned paste or electrolyte overflow, smell - smell whether there is a strange smell. Then measure the resistance value of the power supply input. If less than 20OkΩ, it means that there is a local short-circuit phenomenon at the back end, and then measure the four rectifier diode positive and negative resistance values and two current limiting resistor resistance to see if there is a short circuit or burned; finally, then measure the power supply filter capacitor can be charged and discharged usually, whether the switch power tube is damaged by breakdown, UC3842 and surrounding components are broken, burned, etc... It should be noted that, because it is measured on the road, there is a possibility that the measurement results may be wrong or cause misjudgment, so if necessary, the components can be soldered down to measure. If there is still no such situation, then measure the input power line and output power line for the internal short circuit. In general, in the fuse meltdown fault, rectifier diode, power supply filter capacitor, switching power tube, UC3842 is vulnerable parts, the probability of damage up to 95% or more, to focus on checking these components, it is easy to troubleshoot.

2. No DC voltage output or voltage output is unstable

If the fuse is intact, under the inert condition of the load. This type of failure causes: overvoltage, overcurrent protection circuit open circuit, short circuit phenomenon; consumption circuit does not work; power supply load is too heavy, high-frequency rectifier filter circuit rectifier diode is broken: filter capacitor leakage, etc...

Maintenance method: First, use a multimeter to measure whether the components of the high-frequency pulse transformer are damaged: exclude the high-frequency rectifier diode breakdown, load short-circuit situation, and then measure the DC voltage at the output. If the output is still zero, it is certain that the power supply control circuit is faulty. And finally, use a multimeter to statically measure the high-frequency filter circuit rectifier diode, and low-voltage filter capacitor is damaged. If the above components are damaged, replace the new components, and the general fault can be eliminated. However, we should note that: if the output line is broken or open solder, false welding will also cause this failure in the maintenance should pay attention to this situation.

3. No DC voltage output, but the fuse is intact

This phenomenon indicates that the charger does not work or work in the protection state.

Repair method: First of all, the charger should be judged whether the variable control chip UC3842 is in working condition or has been damaged. Specific judgment is the power to test the UC3842 7 feet for grounding voltage. If the 7 feet voltage is normal and 8 feet have +5 ∨ voltage, 1, 2, 4, 6 feet will also have different voltages, then the circuit has been activated, UC3842 basic normal. If the 7 pin voltage is low, the rest of the pin has no voltage, which means that the UC3842 has been damaged. The most common damage is 7 feet to ground breakdown, 6, 7 feet to ground breakdown, and 1, 7 feet to ground breakdown. If these pins are not broken, and the charger still can not start normally, it also indicates that the UC3842 has been damaged and should be directly replaced. If the chip is not judged to be bad, the switch is to check whether the current limiting resistor of the gate is open solder, false solder, or variable value and the switch power tube itself is poor performance. In addition to this, the power supply output line disconnection or poor contact can also cause this failure, so the maintenance should also pay attention.