1: High voltage fault
2; Low voltage fault
3: Both high and low voltage have faults. The main phenomenon of high-voltage faults is that the indicator light is not on, characterized by a blown fuse, breakdown of rectifier diode D1, and bulging or bursting of capacitor C11. Q1 breakdown, R25 open circuit. Pin 7 of U1 is short circuited to ground. R5 open circuit, U1 has no starting voltage. Replace the above components to repair. If pin 7 of U1 has a voltage of 11V or above and pin 8 has a voltage of 5V, it indicates that U1 is basically normal. Key attention should be paid to checking whether there is solder joint on the pins of Q1 and T1. If Q1 is continuously broken down and Q1 does not heat up, it is generally D2 and C4 that fail. If Q1 is broken down and hot up, it is generally due to leakage or short circuit in the low-voltage part, excessive or abnormal pulse waveform of UC3842's 6-pin output. The switching loss and heat generation of Q1 increase significantly, causing Q1 to overheat and burn out. Other phenomena of high voltage faults include flashing indicator lights, low and unstable output voltage, usually due to virtual soldering on the T1 pin, open circuit in D3 and R12, and no working power supply in TL3842 and its peripheral circuits. Another rare high-voltage fault is that the output voltage is too high to 120V or above, usually caused by U2 failure, R13 open circuit, or U3 breakdown, causing the voltage on pin 2 of U1 to drop and pin 6 to send out an ultra wide pulse. At this time, it is not allowed to power on for a long time, otherwise it will seriously burn out the low-voltage circuit. Most low-voltage faults are caused by the reverse connection between the charger and the positive and negative terminals of the battery, resulting in R27 burning out and LM358 breakdown. The phenomenon is that the red light is always on, the green light is not on, the output voltage is low, or the output voltage is close to 0V. Replace the above components to repair it. In addition, due to the jitter of W2, the output voltage drifts. If the output voltage is too high, the battery will be overcharged, seriously dehydrated, and overheated, ultimately leading to thermal runaway and battery explosion. If the output voltage is too low, it will cause the battery to be under charged. When there are faults in both high and low voltage circuits, before powering on, all diodes, transistors, optocouplers 4N35, field-effect transistors, electrolytic capacitors, integrated circuits, R25, R5, R12, R27, especially D4 (16A60V, fast recovery diodes), C10 (63V, 470UF) should be comprehensively tested. Avoid blindly powering on to further expand the fault range. Some chargers have special functions such as anti reverse connection and anti short circuit at their output terminals. In fact, it means adding an additional relay at the output end. In the case of reverse connection or short circuit, the relay does not work and the charger has no voltage output. Some chargers also have anti reverse connection and anti short circuit functions, which are different from the principles introduced earlier. The starting voltage of their low-voltage circuit is provided by the charging pool and connected to a diode (anti reverse connection). After the power supply starts up normally, the charger will provide low-voltage working power.

• The three common fau…