Method and step for judging module power failure.The cause of the low voltage is related to the various parts of the module power supply and all the circuits related to the module power supply.The fault range should be narrowed down during maintenance.
(1)First measure the c-pole voltage of the switch tube and confirm that the power supply of the switch tube is normal.
(2)Determine the fault according to the voltage of each output terminal of the module power supply.
The output voltage of the module power supply is normal,and some are lower than normal.The rectifier output circuit with low output voltage should check and replace the current limiting resistor,rectifier diode and filter capacitor in the circuit.If the current limiting resistor is hot,the load is over-current and the load is checked.
The module power supply output is low.This situation shows that the load and rectification output circuits are normal,the fault is in the positive feedback circuit of the module power supply,the pulse width adjustment,the open/standby circuit,and the protection circuit.
The output voltage has a large proportion of falling,and some output voltages have a small percentage of decline.The measurement results show that the fault has a large proportion of the output voltage drop.At this point,the load can be disconnected.If the line circuit is disconnected,the dummy load should be connected.After disconnecting the load,measure the voltage of each output terminal of the module power supply.If it returns to normal,it can be judged that the load of the broken circuit has an overcurrent phenomenon.If it is still not normal,the fault is in the rectification filter circuit.
Disconnect the main load and connect the lamp to determine if the load is faulty.
Some machines with flashovers and unstable voltages after loading are difficult to identify faults.When power or load is used,you can use the"borrowing method"to use another power line with the same size and the same B+voltage.,make judgments.
The startup,positive feedback,soft start,and negative feedback circuits are reserved.
Various protection circuits and standby control circuit terminal transistors are eliminated one by one.Turn on the power to see if the fault is eliminated,and gradually reduce the fault range.
Note:Circuits that have voltage regulation cannot be disconnected(eg optocouplers).Care should be taken when disconnecting the protection circuit and measures to prevent voltage rise.
An alternative method is used to overhaul the pulse width adjustment circuit.Replace the original sampling circuit with a self-made sampling circuit to determine the fault range.
(1)After the replacement,the voltage returns to normal,indicating that the fault is in the sampling circuit and the optocoupler circuit.
(2)If the voltage is still low,disconnect the original sampling circuit B+access point.If the voltage is still low,check the B+filter capacitor.After confirming the good condition,the fault can be delineated in the hot bottom plate.First check if the soft start circuit is shunting the switch B pole.Still not,check positive feedback,negative feedback circuit.
The negative feedback method of the hot-spot bottom plate section is similar to the method of checking the high voltage,and the idea offorcing the B+output to be high is adopted(note:changing the working point cannot cause the B+to be too high to expand the fault).
In short,in the maintenance of the power supply,when the voltage is unstable,reverse thinking can be used.When the voltage is high,it becomes low,and when the voltage is low,it becomes high.If necessary,the operating point voltage can be artificially changed.In order to find the point of failure,the maintenance personnel are flexible.