ROBOT.LK

it is a rectifier of ups.it is rectify 230V.it take few mA from main(230V) because,copper wire of PCB is thin.it was feired.but,only one diode has leaked of 4.load resistance has been increased.
what is reason for this.?
if replace diode,will correct?

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It could be mostly due to high voltage. Lightning could damage the bridge as well if it passes through the fuse. As you are saying, if it is just a diode on the bridge rectifier, it should be okay to replace it. However you will have to check whether other components after that is also affected due to the leakage. Start by replacing the diode.