I repaired an smps power supply with 18 volts output
Replaced two shorted UF 2004 diodes with UF4007 and the unit started and output obtained. But the moment i connected the load the output drops all the way down to 14 volts. and the flyback transformer overheats.
Is it because of part incompatibility or....?

 

I repaired an smps power supply with 18 volts output
Replaced two shorted UF 2004 diodes with UF4007 and the unit started and output obtained. But the moment i connected the load the output drops all the way down to 14 volts. and the flyback transformer overheats.
Is it because of part incompatibility or....?

It depends on what the replaced diodes were doing in the circuit, and the damage to other parts when those diodes shorted. I can't believe the damage was localized to the diodes. Can you provide us with a schematic diagram?

 

In my previous post i mistakenly wrote UF 4007 instead of UF4001.
Problem is the ultrafast diode UF2004 originally on the board was shorted and couldn't find it on time and replaced it with UF 4001.
The output was fine (18 volts ).
But the moment i connect a load it drops down to 14 volts and the transformer gets overheated and emits some hissing sound.
Is it because of part incompatibility or it is something else?
Point is there are no shorted components, no dried up caps.

 

It depends on what the replaced diodes were doing in the circuit, and the damage to other parts when those diodes shorted. I can't believe the damage was localized to the diodes. Can you provide us with a schematic diagram?

The point is I've located a shorted non electrolytic capacitor at the Vcc pin of a certain IC Which caused the diodes short.
replaced with good one.it is after doing this i restored the output

 

It is generally a good idea to check all the electrolytic caps too. Whee the capacitors fail, among other things, high voltage spikes that were filtered out are no longer and these can cause failures. Use low ESR caps. Often these caps failing is the root cause of the problems.