SMPS going off in sec

[sankatbaba]

Few days before my smps was remaining on even after I had shutdown the windows. 2 days before suddenly the system went off on its own. And now the problem is when I try to swith on, the processor fan rotates for a second even the smps fan does the same work and then goes off.
I Completely isolated the smps from ******board and tried to turn it on by shorting the green wire with a com. wire but the still the same picture. then i cleaned the smps pcb for any dried glue remainings and the dust contaminents. Suddenly Yesterday night smps fan remained on without any other load on the psu. I thought it solved my problem. So I connected it back to the MB and made all the connections as usual. System remained on and prpperly working for around 5 min and then suddenly went off as it went of previously. Now the ******board led stays on, also the cpu fan rotates for a secnd & goes off. Green wire showing me 4.5v but the none of the other wires have supply.Kindly tell me as exectly which section of smps is giving me the problem. Its alredy out of warranty so now I can go for self repair.
there are no blown components. And one of the filter capacitor(Ac)side 330uF,200v when I connect tester to the top metal portion it shos current in it. What is the problem???

Thanks!
sankat.....

 

[KX36]

Perhaps try cleaning the connector contacts on the output cables, and maybe try one of those ATX PSU testers with the LCD you can get quite cheaply these days. Other than that, look for any signs of damage, look for bad solder joints, bulging/leaking capacitors etc. Check the voltage on each output, check the PS_ON and PWR_OK pins on the ATX connector are behaving correctly.

 

[sankatbaba]

-)Thanx for the reply KX36, hope I will have it all d time in future........anyways back to d topic

Sory here for the late delay. Actualy while testing primary section of smps I burned out some componenets n now they r restored back.

I have done almost everything wat you have told. Smps turns on when I short the PS_ON with COM. I have all the votages present at their respective outputs. Smps fan rotates n the situation looks to be stable but not more than around 10 min max. Sudenly it goes off. All the voltages goes to zero. Only PS ON shows around 4.5 volts. Now again if remove the jumper between PS ON and com and try to connect it back the smps fan rotates for not more than 3 to 5 sec. This is the first scenario.

Moving on to next if I connect the 20 pin atx connector to the MB and try to power on, processor fan simply rotates for 2 to 3 sec n turns off.
Now rather than connecting Mb as load if I connect one more 12 v smps fan it works fine, but again i said only for around 8 to 10 min.

I suspect that their might be problem in the secondary side. Might be when I load it with more components the current level exceeds the safe limiting value as a result it leads to the power shutdown??

I have an optocoupler ic for feedback. I recheked the ic n all the related component such as Regulator IC TL431,resistors. All seem ok.
My pwm ic is SDC7500 n SDC339 comparator IC. What might be causing the excessing current to trip the circuit?? Resistor,zener?.?

Hope will get the help soon!

;ww: