1 fuse fuse
In general, the fuse tube fuse shows that the internal circuit of the charger is short circuit or over current fault. This is because the charger for a long time to work in high voltage, large current state, the high failure rate caused by internal devices. In addition, the fluctuations in the power grid voltage, surge will cause the current surge in the charger to fuse the fuse.
Maintenance methods: first carefully check the each element of the circuit board, see the appearance of these elements is burnt or electrolyte overflow, smell, smell is ignorant. Before measuring the power input end of the resistance value, if less than 20Ok Omega, the back-end of the local short-circuit phenomenon, were measured and the four rectifier diodes are reverse resistance value and a current limiting resistor of resistance, short circuit or burn out; finally measurement power supply filter capacitor can charge and discharge normally, switching power tube is breakdown, UC3842 and surrounding elements of breakdown, burned. Need to be explained, because it is in the road measurement, it may cause the measurement results are wrong or cause miscarriage of justice, and therefore, when necessary, the components can be measured. If there is still no such case, then measure the input power cord and the output power line is short circuit. In general, in the fuse, fuse fault, rectifier diode, power supply filter capacitor, switching power tube, UC3842 is wearing parts, the probability of damage up to 95% above, to check on these components, it is easy to remove the faults.
2 no DC voltage output or voltage output is not stable
If the fuse is intact, in the load condition under. The fault reasons are: over voltage, over current protection circuit and open circuit, short circuit phenomenon; vibration tuberculosis circuit does not work; a heavy load on the power supply, high-frequency rectifying filter circuit of the rectifying diode breakdown: filter capacitor leakage.
Maintenance methods: first of all, meter to measure the high frequency pulse transformer components are damaged: removing the high frequency rectifier diode breakdown, short circuit load, and then measure the output DC voltage with million ammeter with, if this output is zero, there must be a fault on the power source control circuit. Finally, the multimeter in the static measurement of high frequency filter circuit rectifier diode and a low voltage filter capacitor is damaged, if the components are damaged, replace components, the general failure can be excluded. But take note: output line disconnection or open welding, weld will cause this failure, maintenance should pay attention to this situation.
3 no DC voltage output, but the fuse is in good condition
This phenomenon shows that the charger is not working, or after work to enter the state of protection.
Maintenance method: first of all, it should be judged whether the charger is in the variable control chip UC3842 in the state of work or have been damaged. Specific judgment method is: power measuring UC3842 7 feet to ground voltage, if 7 pin voltage is normal and 8 feet a + 5 V voltage, 1, 2, 4, 6 feet will have different voltage, circuit has been startup UC3842 is basic and normal. If the 7 pin voltage is low, and the rest of the tube foot no voltage, then the UC3842 is damaged. The most common damage is 7 feet to ground breakdown, 6, 7 feet to ground breakdown and 1, 7 foot to ground breakdown. If the foot is not broken, and the charger can not normally start, but also shows that the UC3842 has been damaged, should be replaced directly. To determine if the chip is not bad, a checking switch gate which limit the flow resistance is open welding, weld or variable value and switch power tube itself is bad performance. In addition, the power output line disconnection or poor contact will also cause this failure, so in the maintenance should also pay attention to.
