Maintenance method of switching power supply circuit board:
The optocoupler U1 can be used as the dividing line to divide the circuit into two parts, the input side and the output side. In the online or offline state, the power supply for the input side circuit and the output side circuit of U1 is provided respectively, and the maintenance of the small oscillation board is completed separately. and fault acknowledgment.
Connect the DC power supply within 16~24V from the VG+ and VG- terminals to meet the start-up working conditions of the oscillator chip. Attention, if it is in the offline state, the 3rd pin of 3844B must be short-circuited with the 5th pin temporarily, in case the static high level is formed due to the floating of the 3rd pin, which will cause the internal current protection circuit to act and prohibit the output of the pulse signal of the 6th pin! At this time, if the oscillator chip U2 and peripheral circuit components are good, then use the DC voltage block, and the following working voltage can be measured:
1. First, a stable 5V voltage can be detected at pin 8 of U2;
2. Subsequently, the oscillating (stable) voltage output within 2~4V is detected at the 4 pin of U2;
3. Subsequently, a pulse signal voltage output above 6V is detected at pin 6 of U2.
For the above tests, if the tests in steps 1 and 2 are abnormal, replace U2 and try again. If the detection of steps 1 and 2 is normal, and the pulse voltage output cannot be detected at pin 6, first make sure that pin 3 is connected to 0V low level (if it is not low level, temporarily short-circuit pin 3 and 5 to make it low level) , and then check whether pin 1 is much higher than 1V. If the voltage of pin 1 is low, check the peripheral circuit of pin 1 for leakage or short circuit components. After eliminating, make the voltage of pin 1 rise to within 3~8V, and then A normal pulse signal output was detected at pin 6.
