SMPS repair help

steppler

New member
Hello friends,

I want to repair supply driver, but i can't identify some components. Please help me. I attach schematic. Disputed components marked "?"

Thank You
 

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Silvio

Member
Hello friends,

I want to repair supply driver, but i can't identify some components. Please help me. I attach schematic. Disputed components marked "?"

Thank You
Hello I have been looking at the circuit and I can see that the front part near the gates is the auxiliary supply. This will get a voltage from the 1nF capacitor and stabilizes it to 15v hence dropping a little further with the series diode will provide around 14.2v to supply pin 1 thus cutting off the current from the start up resistor.
The second part at the back this seems some kind of shut down circuit tied to pin 3 which hence when operational will pull pin 3 to ground. I did not understand it very well but it can be some kind of delay maybe to let the capacitor tied to the start up charge up properly prior oscillation begin so that a good charge with adequate voltage is available on start up.
Is this circuit mal functioning? if so and not starting up please check that you have at least 10v at pin 1 otherwise the chip will not start oscillation. You also need to check pin 3 and see that it is not shunted to ground with the transistor across it.
Some cheap chips from China need more current than genuine ones and will fail to start.

Good luck in your repair Silvio
 
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