Computer Power Unit Failure

I have an Amacrox AX550-S power unit. Yesterday when um going to power on(before the pressing start button) the PC by connecting power leads to AC, there came a sparking sound from the power unit & cut off the trip switch in the panel-board in my home knowing a short circuit.

So i took the PSU out of the case & powered it again, still the same(no any sparking sound, but the trip went off)
So i removed the case & watch for any burn marks in its PCB. But nothing in PCB. But there was a burn mark on the coil of an Inductor. That was the only burn mark that had.

But when i checked for continuity in power unit for short circuit, nothing short circuited.
meter reads it as open circuit. But why is the trip cut off, meaning that there is a short circuit in the PSU. (means without a load it is open circuit, but with a load its short circuit)



Thank You.

 

Please someone help me... do replacing that burnt inductor will solve this problem(short circuit) ??

 

Thank you very much for all the replies.

 

yes u`re correct. I thought it has burnt. But it`s not. That`s the way it came, i guess.

 

no....never....
As i said the issue is coming from before powering on the PSU. means when i connect the PSU to the AC supply.
Also any PSU can jump start by contacting the switching wire(usually the Green Wire) to the ground of the PSU

 

yeah it`s not.
it`s(the PSU) do open circuit when there is no load.(when not connected to AC power)

 

yeah...there have some inductors connected series and suppression capacitors connected in parallel in the very first(there the main power inputed to the circuit) of the circuit. Right after them, there are two bridge rectifiers connected in parallel. I got that out from the PCB and checked them. Nothing wrong with them too. Knowing that the fault is in further more ahead.

yeah.. there have a big big electrolytic capacitor(420uF 420V). I checked it with ohms as my multimeter(my one is range from 4nF to 400nF) is not enough to check higher Farads.


anyway when i went further ahead(after those bridge rectifier) there have some switching transistors with the heatsink. wait i have to check those ones now....
I`ll tell what happened.
Also can i power the PSU(connecting to the AC power) by removing any component and see whether the power unit is not short circuited.? Then if it`s not short circuited i can determine that the fault is coming from that removed component. eh ? (i know that removing any component connected parallely will not understand where the fault is)

 

yeah it`s a normal circuit breaker.

No, it(the power unit) cannot be a earth leakage. Also i powered the PSU without connecting it to the Ground(the earth wire).Still the same. Trip went off.

And also sometimes it will not cut of the trip, it will blow a fuse in the plug of the AC connecting wire. Knowing not a earth leakage but a short circuit. That`s because of a faulty burnt part.

 

oh yeah...
finally figured out that one of the switching transistors(part no - F25NM60N) is gone.
Will replace it and say what happened. (Also there might be any other faulty parts that left too. Will see !!)



thank you all in Advance....

 

yeah thank you guys......these were very helpful, also other ones too

 

guys believe me.... seriously i couldn`t find that "STF25NM60N" transistor in here, Sri Lanka. I searched it for everywhere but still no luck.
I thought of replacing it with a same characteristic(equivalent) transistor. Guys any suggestions please ?
What is the best equivalent transistor for that "STF25NM60N" ?

Please help me dudes...Thank You.

 

Thank you so much dude.....what about these ?
Firstly "STF25NM60ND"
then this "MTP20N10" or this "MTP20N10E"

those can be found here easily....
if neither of them are not recommending by you then i`ll go for your "STF34NM60ND" one


THANK YOU again