450w computer smps problem troubleshhoting

[tpetar]

It's not mandatory to have this switch; this switch cut power from grid and obviously all outputs go to zero. This swith is to isolate power supply from grid and it's not Power-on switch according ATX specifications.

No one says that this switch turn on PSU. I disagree with you, this is mandatory switch, cant go in EU market, I supose and other markets, and I didnt see recently new PSU without this switch.

Can you read my post #19, I quoted what you said in your post #18, I mean on red part.

:wink:

 

[peter_england]

Hi peter,
It is normal to have +5v at the time of starting it is used as starting pulse to turn on the smps. let us go systematic can you please tell which IC is used in your smps is it TL494 or KA7500 or IC 2003 or any other ic please give details.
regards ani

Hi Picgak Thanks

Ic used in that smps is Weltrend WT7525 ..


I am waiting for your replay >

 

[picgak]

peter does the circuit attached similar to that of your smps

 

[peter_england]

Ok thanks for diagram i will check it and reply.

(ignore my Bad English.)

 

[Doom2pro]

I have seen this so many times, the fan spins for a short period of time because the supply is starting up (for a short period of time) and over current detection is kicking in and shutting the power supply down. This means one of your output rectifiers is dead, or half of a common cathode rectifier is dead and shorted. If you find that this is not the case, another possible reason for premature shutdown is one or more rails are out of spec, too low or too high and the regulation circuitry is shutting the supply down to protect the load. Possible causes are dead or dying output capacitors (rail too low) or dodgy feedback circuitry (rail too high).