Help fixing an Antec True550

[Gauss]

Hi everyone, I have a big problem in my hands. I bought an Antec True550 and after almost 2 months of use something terrible happened, something burned inside when it made a big noise and the system shuted down.

Then I had to decide what to do, to RMA it back or to try fix it myself. I have to mention that I got this PSU through many transactions and freights since it's not available in my country, nor any quality PSU. I decided to try fix it myself, since many freights for the RMA would cost me the half I paid for it (just the same a new one cost in USA) and a lot of time.

So I found that the fuse was blown and decided to change it, but for my big deception as soon as I gave it power another blown fuse I had. I realized by testing the outputs before that all outputs are in shortcircuit with a difference of less than 50 Ohms but thought that that was simply a protection for short circuit since the manual says that all outputs are set to ground.

So now I think that maybe something else is wrong in the PSU and that I most change that part, that's what my message is intented, to request any kind of help, maybe a circuit diagram of this power supply , suggestions to find a burned devices, etc. I've already taken a look thoroughly and not a single capacitor or transistor seems burned, but maybe I shoud also check them with a multimiter.

Any suggestion to check transistors?

Please help! I would really appreciate real help.

 

[svend]

Since the main fuse is blown i would be checking also the bridge rectifier circuit, and if you heard a "bang" look for some damaged components, to check the rectifier use an omh meter and check front to back and then back to front. one direction should be k ohms and the other meg ohms, Just think of a diode. the bridge rectifier is 4 diodes. This is usually the common part that fails in power supplies. Also if you are in a different country make sure the AC power selection was correct. if the bridge rectifier is ok then i'd look for a zenor diode that was shorted to ground. good luck

when all is said and done, what you've done for your neighbor is most important

 

[Gauss]

Thanks for replying svend,

The switch its in it´s right position, 115V (America). I´ve already checked the PSU and found the main cause of this, I think, seems it was a mosfet, one ST W11NB80. I can´t find it here in my country, I´ve just found the ST W8NB100, compared data sheets and they are very simliar, they can be used in the same aplications except high current ones, where the W11NB80 it´s for that.

I´m not really sure it this chip I found is a good replacement. This "thing" (PSU) uses 2 so I decided to change both since they are together in the circuit, also found many diodes damaged near these mosfets, all other things seems well. Maybe one of those diodes failed and made that mosfet to burn.

So I replaced everything damaged I could found. Now the thing doesn´t make a short circuit when powered, but the fuse blows again. I dismounted the transformer and when powered again the fuse doesn´t blows. So I thought that also something in the DC side is damaged, but didn´t found something. Now I´m thinking that the transformer is damaged, but I´m not sure how to probe it, if I test impedance from one side to another it has 0 Ohms, I think that´s right since one side never makes contact with the other in a transformer.

How can I test a transformer?
Anyway if this thing is damaged I think it´s a lost case. But I still have hopes.