PSU acting like bad caps after replacing

[envoid]

Re: PSU acting like bad caps after replacing

These three were pulled from the FX600-GLN that was the "other" PSU. Same issue after the caps were installed... Before the caps they were fine on both PSUs. Well, fine as in all was fine before the caps crapped out.

I'm thinking of scrapping these things and just stripping what seems good or what I just put in. Kinda the last straw but unless I try swapping the main cap (which means buying one and with my current budget it would only happen if it definitely fixed it) there's not much more to do. Also kinda don't want to do it as I liked these units, especially the blue paint. Not finding that any more.

It's just odd to me, though, that after replacing the caps it acts worse. Like the FR's are causing an issue...

[Toasty]

Re: PSU acting like bad caps after replacing

The FR's could be. Are you sure you installed -all- the caps correctly (polarity)?
Did you make a "cap map" before you removed the old ones?
Did you get the FR's from a reliable source? (no fakes)
Are you certain you don't have any "solder bridges"?

You relate the blown MOSFET to the bad caps. I doubt that is true. The only cap I see as a possible cause for concern is the mains cap which could directly cause the MOSFETs to blow. All the other ones are on the other side of the PSU and while their failures could cause the PSU to shut down, I don't see them causing the MOSFET failures.

Checked the single board mounted diode next to the Mains cap?
You did replace the 2 little caps near the 5VSB? On either side of the center heatsink.

Toast

[PCBONEZ]

Re: PSU acting like bad caps after replacing

The cap in the heatshrink against the heatsink is the panny 2200uf/6.3v I somehow now was able to get in. It is CAP4 on the underside image. (this was initially an OST 2200uf/16v that I replaced with a 2200/6.3v Nichi HM)

A 16v cap is most likely on 12v.
If so then a 6.3v cap won't do.
.

[envoid]

Re: PSU acting like bad caps after replacing

Bonez, they seemed to have used just two different caps for everything, the OST 2200uf/16v and the CapXon 1000uf/16v (minus those tiny ones and the mains). The OST that I replaced with the Panny FM is on the 3.3v line. I traced them I think four times now just to make sure I wasn't seeing things or missing something.

I triple-checked the polarities as I wondered that as well. Also combed over the areas for bridges and made sure the caps matched where they should be.

I checked the diode before and was getting resistance both ways (out of the circuit) so pulled the one from the "other" PSU which seemed good. But no difference.

I replaced all the caps on the secondary side from the heatsink to the output wires except those two OST caps. Anything from that heatsink and over to the primary side has not been touched except for the blown MOSFET and diode swap. I think those two small caps are there which you are talking about, Toast?

I had thought that the secondary is causing the problem because the MOSFET doesn't blow unless a heavy load is placed on the outputs. The tester just makes the PSU sound like crap (kinda like arcing) and you see the lights for the lines on the tester flicker. Supplying mains to the unit doesn't make it fail, it actually sits ok with the 5vSB line working ok, but it isn't drawing much then either. And I'm definitely not an expert in SMPS so I'm probably not even close.

What would happen if the wrong voltage cap was put in place? I've never seen this and thought it would pop the cap.

THank you guys!!

[envoid]

Re: PSU acting like bad caps after replacing

Btw, Happy Thanksgiving!

[PCBONEZ]

Re: PSU acting like bad caps after replacing

What would happen if the wrong voltage cap was put in place? I've never seen this and thought it would pop the cap.

It can pop caps but I don't think a 6.3v cap on 12v would be that dramatic.
It's double but it's still only about 6 volts.
.
The dielectric in lytic and poly caps is an aluminum oxide layer on the aluminum foil.
[The saturated paper or poly material is actually just a pathway for the electrons to move in, it's a conductor not a dielectric.]
The voltage rating is based on how thick the oxide layer is.
With too much bias applied for the thickness of the layer the electrons can be rammed right through the dielectric [aka excessive leakage] which will degrade the layer allowing even more leakage.
[Leakage 'Runaway' might be a good name for it.]
- Ultimately you end up with a shorted cap.
.

[envoid]

Re: PSU acting like bad caps after replacing

Thank you, Bonez, for clarifying that. Makes sense now. I just wish this damn PSU made sense.

This situation reminds me of an old LCD TV I was messing with. It blew its MOSFET and then the fuse but then someone (not me) jumpered the fuse and blew the board. I repaired/replaced the burnt up parts but it still wouldn't give voltage. It had the primary side and the standby voltage all fine, just not the secondary side like here, well sorta. I gave up on it as I was more into it than I wanted to be and I could never get it to work past that, and now it feels like it has returned twice-fold.

[envoid]

Re: PSU acting like bad caps after replacing

Sorry to bring this thread back from the dead, I just wanted to make sure everyone knew my appreciation for the help from everyone, especially Toasty. Thank you!

And for closure, I've decided to just steal parts from these PSUs and get a new one. If I had more time I might try more things...

[envoid]

Re: PSU acting like bad caps after replacing

Hi guys.

I got some time again and am looking at the 700w PSU again (left them in a corner in the basement since). I found a bad/weak solder joint on the APFC board but also two resistors with 0 ohms.

I'm thinking the pink one is 13.8 ohm and the blue as 3.8 ohm but I don't see those as common values. Can anyone help ID these?

thank you!

[ben7]

Re: PSU acting like bad caps after replacing

Did you replace the old capacitors with lower ESR caps? If so, that can - although rarely - make matters worse, as the power supply is designed using output caps of a certain impedance. It messes with the power supplys' regulation.

[envoid]

Re: PSU acting like bad caps after replacing

Hey Ben.

Good info. I tried to get right around the same and from what I remember they were either just around the same ESR or -/+1% or so.