Ultra Xfinity 600w 5vsb mod

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

and the 5vsb cap in question is likely the 50v 10uf one?

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

The killer 5vsb cap is usually near the primary heat sink toward the back of the PSU. If that's where it is on this power supply, then that could well be it.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

it is... it is also near the 5vsb lead. also nearby are two 680uf 16V caps and a coil between them... dang I wish I was better at psu modding...

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

Could we have a picture of the PCB from the back?

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

sure.



the components I spoke of are all in the foreground.

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

That's an interesting design. the killer cap is usually located somewhere in the red shaded area of the attached picture, but if there are no small caps there, my best guess would be the 10uf 50v in front of the two bigger ones (the one I think you've been referring to)

[momaka]

Re: Ultra Xfinity 600w 5vsb mod

it is... it is also near the 5vsb lead. also nearby are two 680uf 16V caps and a coil between them...

That's the secondary side, not the primary.

Killer cap is usually on the primary side, by the primary heatsink and 5vsb MOSFET as c_hegge mentioned. Not all 2-transistor 5vsb circuits have the killer cap, though. My Macron MPT-301 is an example of that.

Flip the PSU board and see where the traces for that 50v, 10uF cap are going to. If you see them going to the opto-coupler by the 5vsb transformer, then replace it. And if you don't, replace it anyways - Canicons aren't that great.

The two 16v, 680uF caps should also be replaced. 6.3v/10v @ 1000uF is usually more appropriate for that.
I'm also guessing R19 (100 Ohms, right by one of the 16v, 680uF caps) is the minimum load resistor for the 5vsb. If it's connected between 5vsb and ground, then that's what it is indeed. 100 Ohms is a good value, but if you have a 1W resistor or higher of that same value, then replace that as well. I believe the one in the current spot for R19 is 1/2 watt - probably gets pretty hot. Not good for the 16v 680uF 5vsb filtering cap near it. 1W should run a bit cooler.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

well jeez, replacing all the little caps in this beast would take forever... it is full of tiny caps.

i thought he said secondary, my bad there.

noting on the primary side, connected to pin 1 of the optocoupler is the positive lead of the righthand 680uf 16v cap and the coil. on the other side of the coil is the positive lead of the other 680uf 16v cap. the negative leads of both caps are grounded.

the negative lead of the 10v 10uf cap is connected to the coil ^ via a diode.

the 100 ohm resistor in question is between the coil and ground, looks to be the loading resistor.

also worth noting is that pin 1 of the optocoupler is also connected to a bigass diode, which is connected to the 5vsb transformer.

it looks like I found the wrong cap... suggestions?

edit- the other side of the coil is also the 5vsb. that resistor is in fact the load resistor, and the 10uf 50v cap is likely out of circuit.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

ok, i think i more or less have the circuit figured out:

• the transofromer goes to the large diode, which acts as a 1/4 bridge, creatign pused DC power
• from there, it goes to pin 1 of the optocoupler, the input of the coil, and the positive lead of the capacitor 1 (680uf 16v)
• the other side of the coil is connected to a load resitor (100 ohm), the positive lead of capacitor 2 (680uf 16v), and the 5vsb output
• the two capacitors and the load resistor connect to ground

from what i see, the two 680uf caps are the killer caps, especially capacitor 2. they also suppress ripple, depulsing the dc power coming from the diode and transformer.

therefore, the only idea i can think of is to change the load resistor (more watts at the least) and to find some high temp 'lytics' for the two capacitors. Right now I have my list set to nichicon HE, since other circuits use that value; however, I may look for soemhtign more temp resistant.

my analaysis correct?

[shovenose]

Re: Ultra Xfinity 600w 5vsb mod

Hmm... can't you just replace all the crap caps, then it wouldn't matter which one is the "killer" cap
Even thought you're going to have a killer time replacing all those little suckers

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

Hmm... can't you just replace all the crap caps, then it wouldn't matter which one is the "killer" cap
Even thought you're going to have a killer time replacing all those little suckers

real line one of my last post.

beat you tot he punch more or less

[mockingbird]

Re: Ultra Xfinity 600w 5vsb mod

replacing all the little caps in this beast would take forever... it is full of tiny caps.

Are you serious!? I've got like 5 PSUs here that have been sitting here for months... I've been going over the recap for a while, a little time here, a little time there. Tommorow I'm about to order $100 worth of caps, and yes, I'm replacing every little cap I can get to, except for those on the PFC and PWM vertical boards that are impossible to get to or are just coupling caps...

My point is you should take your time, plan it out carefully, research, research again, and then go ahead and recap it. I've detailed sheets for all my PSUs, diagrams of how to resolder the wires when I want to put it back in the case, detailed lists of the capacitors... Tommorow I'm making the order, and I'm still making some small modifications.

If my recap is successful, then I basically have a documented routine for re-capping that particular model.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

well, dependign on what route i take with my older oldskool rig project, I may need the psu to be ruuning somehat soon.

looking at the psu, there are 8 tiny caps, with quite a few mounted/buiried in ways that make it ivery difficult to get any info on specs. getting them out may be a challenge.

what I had always read is that if it is under 470uf, unless in certain cases, don't mess with it.


the current part list:

4x 680uf 16v (2 in the 5vsb circuit, see post #29)
3x 3300 uf 10v
2x 6800uf 16v
1x 4700 uf 10v
1x 100 ohm 1W resitor

from the tiny caps, I can find:

10uf 50v
1uf 150v
2.2uf 50v
22uf 50v
0.22uf 50v

there are 4 i cannot get specs on w/o desoldering them, 2 of which are buired between the primary heatsink and the driver transformer.

I would rather not fuss with the tiny caps... especially the really hard to get to ones.

[momaka]

Re: Ultra Xfinity 600w 5vsb mod

from what i see, the two 680uf caps are the killer caps, especially capacitor 2.

No, those are the 5vsb filter caps.

Looks like your PSU just doesn't have one, just like my Macron.

The 50v, 10uF may be for the VCC rail of the PWM controller.

Right now I have my list set to nichicon HE, since other circuits use that value; however, I may look for soemhtign more temp resistant.

Any good quality low ESR Japanese cap should be fine there. Panasonic FC and FM, Nichicon PM, PW, and HE, and Chemicon KY and KZE are what I've used in the past for small caps like that. I've also used them for the outputs too.

what I had always read is that if it is under 470uf, unless in certain cases, don't mess with it.

This doesn't apply for PSUs, though. It's better to evaluate each PSU individually.

there are 4 i cannot get specs on w/o desoldering them, 2 of which are buired between the primary heatsink and the driver transformer.

If this is a half-bridge PSU, then those 2 caps between the primary heatsink and the driver transformer should also be changed. These caps drive the switching transistors on the primary and they can diminish the PSU efficiency if they begin to develop high-ESR.
Those and the critical "killer" 5vsb cap are the only "small" caps I usually change when recapping a PSU. Occasionally, I also change the cap on the VCC rail of the PWM/supervisory IC if it's a really crappy brand (and by really crappy, I mean Rulycon and the like).

You don't need to change anything below 1uF either.

Replace the 2x 16v 680uF caps with 2x 6.3v 1000uF or 10v 1000uF caps. Should give a bit better filtering on the 5vsb circuit. Don't want to skimp on the 5vsb filtering caps, otherwise be prepared to have S3/Standby issues with your PC.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

okay... so the other question is about those 2 buried caps... gettign in there may require tweezers, as the traces holding down the primary heat sink are lifted (resoldered) and I would rather not remove it.

edit- tweezers won't work. looks like to replace thew caps, i wil have to remove the primary heatsink... which due to the iffy traces, means I could very well kill it tryign to replace those two caps.

I hate having to skimp but if you can't get to the part, you can't.

edit2- if i used braid to desolder it, i think can get back there... but i am still worried about the lifted traces... super glue?

[momaka]

Re: Ultra Xfinity 600w 5vsb mod

okay... so the other question is about those 2 buried caps... gettign in there will require tweezers

There, I fixed that for you .

Actually, I didn't have tweezers for the first 2 PSU I recapped - had to use my fingers and other objects to poke and wiggle the caps out of their spots. Then, to put the new caps in, I had to use a screwdriver with folded tape on it and the new capacitor stuck to the tape to get it back in there. Wasn't too hard or anything, just a bit more time consuming.
Then I got tweezers and everything was much easier. I don't have any high-wattage irons, so for me, desoldering heatsinks or anything with large solder traces is out of the question.
Get creative and I'm sure you'll find ways to get those caps out without desoldering the heatsinks.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

short of a hacksaw, I doubt it... they are more or less enclosed, and due to the shape of the heatsinks and the sixe of the transformers (the heatsinks cover parts of the transformers), gettign in there without sawing heatsinks will require desoldering.

nof if the traces hadn't lifted (punched through, that is, due to a soldring defect), it would be no big deal. however, since one of the anchor traces is an island, it may come off with the solder if I am not careful... hence the issue.

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

If it doesn't have the killer cap, them just replace what you can. As for replacment caps, you won't find anything much more heat resistant than Nichicon HE (High Endurance) series.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

If it doesn't have the killer cap, them just replace what you can. As for replacment caps, you won't find anything much more heat resistant than Nichicon HE (High Endurance) series.

so that's what it stands for.

tm I will desolder the primary heatsink and primary caps to get good access to the 2 little caps.

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

I don't know it that's what it really stands for, but HE are a high endurance series.