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Switching power maintenance

Switching power maintenance

Issue Time:2020-05-08
TITLE:Explanation of common problems and maintenance methods of switching power supply

Common problems in using switching power supply

1. The reason why the fuse of switching power supply was blown

Switch tube/power supply thick module \ rectifier diode breakdown \100uf/400v large capacitor breakdown leakage, and then led to internal demagnetizing resistance rupture;

2. The reason why the switching power supply has no voltage output

Open circuit of safety resistance in ac 220v rectifier filter circuit; The resistance is open between the base of the switch tube and the positive pole of the 100uf/400v large filter capacitor.

3. The reason why the switching power supply will have a small voltage output only at the starting moment

The output tube of the line is broken down. In the switching power supply, the 2.2uf~100uf electrolytic capacitor on the first left of the switching transformer fails and leaks electricity.

5. Reasons for low output voltage of switching power supply

Line output transformer local short circuit pulse width modulation circuit of the audion and diode breakdown "leakage" photocoupler of the audion leakage.

6. The reason for the distortion of the grating and image S and the movement of the black belt in two vertical directions

100 uf? Failure and capacity decline of 400V large filter capacitor.

7. Cause the grating local color spots and image local color wrong reasons

Is the switch power supply ac 220V input circuit in the open circuit resistance

Switching power supply without output maintenance skills

1. There is no reason for the voltage output of the switching power supply

Switching power supply is always no voltage output refers to the switch power output terminal, in the power switch is always 0V, this situation is due to the switch power supply did not produce vibration. The further verification method is to measure the voltage of the switching power supply after 100UF/400V capacitor is turned off. If the voltage drops slowly after 300V, it indicates that the switching power supply does not oscillate. The reasons why the switch power supply does not oscillate are as follows: the collector of the switch tube does not get enough working voltage; The starting voltage and related circuit leakage are not obtained at the base of the switch tube. Failure of positive feedback element of switch tube;

Maintenance fault's first priority is to judge this kind of drum in which parts of the above three parts, the specific method is to measure switch tube collector, the base voltage, may have the following several ways: switch tube collector voltage of 0 v and below 1.4 times, electric switch tube without normal working voltage, if there is 1.4 times of the voltage, that switch tube collector has the normal operating voltage, indicating AC220V and rectifying filter circuit work normally. Switch tube base voltage of 0 V (including instant boot) this kind of situation that starting circuit for switch tube base did not provide a start (conducting) voltage, breakdown, or between the base and emitter element to start circuit and switch tube emitter and related components for inspection, if the voltage is 0.6 ~ 0.7 (including a few moment) and starting circuit and switch tube emitter element is normal, if above 0.7 V startup circuit is normal, but the switch tube emitter junction or its components cut-off or resistance. The switch tube has the conditions of conducting: the base voltage of the switch tube is 0.6-0.7v, and the collector voltage is greater than 250V, indicating that the switch tube has the working conditions, and the fault lies in the positive feedback circuit, including the positive feedback resistance, capacitance, diode and the positive feedback windings of the switch transformer and the connection between them should be fabricated.
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