Power supply repair

[kripton2035]

check the caps with an esr meter... they look the brand that always fail after a couple of (hot) years inside a supply ...
check the small cap beside the vcc pin of the ucc chip. often that one fails.

[Rasz]

check the caps with an esr meter... they look the brand that always fail after a couple of (hot) years inside a supply ...
check the small cap beside the vcc pin of the ucc chip. often that one fails.

judging by your signature you are everything is a hammer type of guy
this is high end HP server supply, caps are most likely fine
as Janoc said earlier UCC3818N does active PFC aka pumps line voltage up to >300V on main cap and keeps power factor as close to 1 as possible. Inverter wouldnt even start without that DC voltage, so I would discount this (but measure DC on main cap to make sure).

Now rereading OPs posts again I have doubts,  rodrigopires did you turn on the supply by shorting proper pins?
http://static.rcgroups.net/forums/attachments/6/1/8/2/5/8/a8177619-247-20150824_004329.jpg

[janoc]

check the caps with an esr meter... they look the brand that always fail after a couple of (hot) years inside a supply ...
check the small cap beside the vcc pin of the ucc chip. often that one fails.

judging by your signature you are everything is a hammer type of guy
this is high end HP server supply, caps are most likely fine

Actually, he has a good point. That little decoupling cap near the main PWM chip (not the UCC PFC controller!) is often a problem.

Also checking the elcos using an ESR meter cannot hurt - even good, brand name caps have limited life and you don't know how long and in what environment (enclosed racks can get pretty toasty!) has this supply been used before the OP has bought it. It certainly isn't new. A dried out cap could give you plenty of grief.

[rodrigopires]

well at this point i think i'm ready to let this one go. I dont have a ESR meter even though the caps are probably fine. My experience isn't enough for this type of repair... I will scrap the supply, desolder every component and test it to find the fault. Hoping i learn more about it and be able to repair the next one that comes. In the end it did came from a junk yard, i will try to see if i find some more but they are hard to come by.

Is the 5V only for auxillary start up or main supply aslo?

The 5V is not just auxiliary it's also a supply output but completely dedicated circuit.

Now rereading OPs posts again I have doubts,  rodrigopires did you turn on the supply by shorting proper pins?

Yes i did, not like this picture, i soldered the small contact with the wire to that tinned contact not to ground, but it must be the same thing because this supply has worked before and the other one i have works perfectly and is the same way.

Thanks everyone for all the help  and i will post my results as i go 

[kripton2035]

an esr meter is an essential tool if you want to fix electronics, especially if they come from junk.
and it's not an expensive meter you can build one from junk with bottom drawer components.
there is even one with only 5 transistors and some passives from an eevblog member jaydaddy.
I'm not "hammering" anyone but take a look at my repository below.
good luck with your repair.

[rodrigopires]

FOUND IT, i think...

So there i was desoldering all the primary and testing components when i come across this. There is a burned diode between the pin 16 (drive output) and pin 1 (ground) of the UCC3818 chip. How could i have missed this  Tested all the "orange" diodes and didnt see this one... I guess that was a protection diode of some sort. Next time i be sure to take a closer look...

Now i have to finish the job and desolder everything. Btw, i was thinking, could i use the big 20N60 mosfets and something like a pwm to supply the high current 12V transformer and make my own little supply from those scrap parts?