Switching power inverter supply has no DC voltage output, but the fuse is intact

This phenomenon indicates that the switching power inverter supply is not working or has entered the protection state after working.
Maintenance method: First of all, it should be judged whether the main control chip UC3842 of the switching power supply is in working condition or damaged. The judgment method is as follows: powering up the voltage of the 7th pin of the UC3842 to the ground. If the 8th pin has a +5V voltage, and the 1, 2, 4, and 6 pins also have different voltages, the circuit has started to vibrate, and the UC3842 is basically Normal; if the voltage of pin 7 is low and the other pins have no voltage or wave, the UC3842 is damaged. The most common damage to the UC3842 chip is the breakdown of the 6 and 7 feet to the ground, the breakdown of the 5, 7 feet to the ground and the breakdown of the 1, 7 feet to the ground. If these feet are broken down and the switching power inverter supply still does not start normally, the UC3842 will be broken and should be replaced directly. If it is judged that the chip is not broken, it is important to check whether the current limiting resistor of the gate (G pole) of the switching power tube is open, soldered, variable, deteriorated, and whether the switching power tube itself has poor performance. In addition, the power inverter output line may also be disconnected or poorly contacted. Therefore, you should also pay attention to check when repairing.