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Reason behind short circuit in SMPS primary side

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imranahmed

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Please let me know that why components in primary side in SMPS battery charger damaged i.e bridge rectifier diodes, switching transistor 10N60, current sense resistor 0.5 ohms, optocoupler and UC3842 at the same time.

What would be a reason behind this failure I repaired three times but same thing occured?
 

How to test primary is shorted or not?

I test with Ohm meter its resistance shows zero ohms.
 

Transformers are a little difficult to test with an ohmmeter. Did you remove the transformer connections from the circuit? Do you know what the primary D.C. Resistance SHOULD be? It could be very low normally.
 

output diodes shorted, sec winding shorted, gate drive to mosfet faulty, the list goes on ...
 

It is understood that after each repair it worked for a while. In cases of repeated defects, all soldering must be checked with a magnifying glass . In the transistor's drain there is a group of components including one or two capacitors. These caps must be carefully measured or better replaced with some of the same type and voltage. The transformer fails in extremely rare cases. Up-load here the electric diagram to comment in detail. Did you check that the electrolytic cap follow the bridge is not o/c ?
 

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