SMPS Power Supply weird problem.

Hello Guys..here i am again...now t-shooting again an smps...this smps when u power initially, it'll give u good output and AC fan spin correctly. But when u turn-off and power on again, the fan spin very slow and the ouput gets only 1.5Vdc only (expected 5Vdc). Ok here's another thing, when i discharged the high voltage dc capacitor and power-on it'll goes back to good condition...Thus, u need to discharge the caps if u want to power-up the second time to maintain good operation....otherwise, it'll gives u bad output and low spin fan

Hope someone can help...thanks a lot.

 

It's an smps for computer (cpu).

 

Yes actually we bought a new one already...but it was installed right away, forgetting to use it for while as reference for t-shooting the faulty one...Now the end user don't want to pull it out again :-(
Anyways, i'll tried to find some tips from other forums....and continue exploring the unit

 

Hello Guys...have some good news on this topic and wanted to share...Got some tips from other forums....anyways, the culprit was the power mosfet...might be switching getting slower for some reason :-( ???

 

Actually that's a sort of wild thinking of mine...the thing i know to discharge this big caps is when the mosfet switching to ground... (not sure)...but the only thing i pretty sure is that when i replaced the mosfets the units goes well.

 

Yes all big caps i'd changed before but not helping...ohh, i never check the resistors

Let's wait for the unit to comeback

 

Yes, we have LCR/ESR meter BK precission 889b model...but the problem is i seldom use it because as far as i know, measuring the parts in-circuit will give u inaccurate reading...you need to remove the part and measure it manually...Is there any tips u can share on this? thanks