Corsair CX400W 5vsb goes into safety loop

[stj]

the uni-t is probably averaging the reading, the transformer is going to mirror the pwm input so the output is not just ac, it's also going to have a varying duty cycle.

you meters can probably do duty-cycle

[Per Hansson]

I replaced the LM431BCZ with a KA431AZ taken from another PSU.
Did not make any difference what so ever.
I also checked all surface mount resistors and they where all in spec.
At this stage I think the issue is with the transformer.
I annoted a picture I posted earlier with the ohm readings I got on it out of circuit.
Due to it's construction I don't think the low ohm measurements mean anything, I take it I need to feed it high frequency DC for it to behave properly?
But then I can't measure it anyway so how do I test a transformer like this one?
It's marked VEE19FB10

[stj]

build a high-speed rectifier with uf4007 or similar,
then follow wih a small low impedence cap - maybe 1uf

if you put that between the transformer and your meter you can watch the input / output voltages even if they are in the mid khz range.

[Behemot]

I once also searched for the transformer, nobody had any. And the last ones when I've been scrapping units incl. Seasonic are already recycled.

Just keep it for a while, sooner or later you'll find some. These Seasonic untis are quite common and mostly the same.

[fzabkar]

Does this transformer have two windings in parallel on the output side??? If so, what happens if you connect only one winding?

[budm]

Originally Posted by Per Hansson

Thanks for your post fzabkar, yes this PSU has turned out difficult to troubleshoot.
Unfortunately I don't have a scope, but according to my multimeter the 5vsb is stable as a rock.
The testing equipment I run from it before it goes into the safety reboot loop also has no problems, so it would imply that it infact is stable.

Yea I think that Zener diode ZD103 is a 18v Zener, it sits between VCC & GND and would be a sensible rating since the FSQ0165 is rated for max 20v on the VCC pin.
It's also sensible from the perspective that this is the voltage I read before the thing goes into the safety loop...
Actually with the new FSQ0165 VCC can go up to 18.2v now before the unit shuts down.
There is also a 100ohm resistor here so the voltage on the FSQ0165 is slightly lower at 16.9v, the Zener diode sits on this side of the resistor too so that's what it sees as well.

The other SMD Zener diode ZD101 I'm not sure about, but it sits on the feedback signal which is rated for up to 9v so I guess it's sensible that's what it's rated for.
As for the TVS diode marked ZD102 on the topside I left that out now for a test, since a big leakage here would case problems since it sits between drain and B+ from the main bulk capacitor, but it made no difference at all.
(The unit also did not blow up and continued working as before so the problem was not here )

I have not connected a sense resistor but I do have a quite accurate power meter to measure the load of the whole PSU.
With nothing connected it shows 0.0w draw.
With a small ~0.4w lightbulb for load it shows 0.4w.
With the lightbulb and a small fiberswitch it shows 3.0w draw.
All of this is sensible because the devices by themselves do draw that amount of power if measured using a DMM in series...
The 5vsb is rated for up to 2.5Ah or 12.5W according to the power rating plate provided on the PSU by Corsair so we are not even close to actually overloading anything...

Having Zener rated higher than the running Voltage on VCC and GND for protection is typical, it also protect the Voltage spike when its first startup before regulation kicks in, some of the IC has the Zener built-into the IC itself, nothing new.

[Per Hansson]

Thanks all for your posts, still deciding on what to try with the transformer

Originally Posted by fzabkar

Does this transformer have two windings in parallel on the output side??? If so, what happens if you connect only one winding?

I took it out again and disconnected the outer cable pair, resistance measurements where unchanged.
Actually it pretty much registers as a dead short, like I assume a pulsed DC transformer should.
I took ESR readings this time instead with my Bob Parker meter; reading is ca 2.2 both on the still connected pair and now disconnected pair.
It was the same before disconnecting as well.
For reference the primary sides auxiliary winding for the controllers voltage reads around 62, so quite different vs the reading I got with the UNI-T DMM.
The primary winding is too high so I can't read the ESR on that.

Originally Posted by stj

build a high-speed rectifier with uf4007 or similar,
then follow wih a small low impedence cap - maybe 1uf

if you put that between the transformer and your meter you can watch the input / output voltages even if they are in the mid khz range.

Not sure I follow here, why does the pulse frequency become so high if I'm only feeding it 50Hz AC?
In any case I don't think I have such a small 400v cap...

[stj]

your not feeding it with 50hz,
that goes into the primary rectifier and cap(s) then gets chopped again by the controller circuit.

[Per Hansson]

stj: ok, well what I wanted to do was test it outside the PSU so nevermind then...

I found a transformer with atleast the same dimensions and similar naming: VEE19FRC1
On my meter I got the exact same readings as the original transformer.
The pinout was different though but I hacked it together by installing the transformer upside down and just used long wires for it :P
Seems the auxiliary winding does not come online though, the voltage is oscillating from around 8v up to 12v.
That's the limit where the chip is supposed to switch from charging the external capacitor using it's internal Vstr pin to where the transformers aux winding should take over.
So either I got the cables reversed or this transformer is too different to be usable.
Also saw on the side of the original transformer that it had some more numbers:
Top: VEE19FB10
Side:
SBI4.2
E150436 C
There exists an UL document for a transformer with that naming, not the exact same pinout though...

[Behemot]

It should be at least from similar Seasonic unit. There are some slight differences in nubmer, maybe because of continuous output current of the rail. I bet this one is different though…VEE19 (something like vertical 19mm sized EE core?) just specifies the core itself so that is quite generic; than the remaining numbers are important.

[rsuga]

A bit off-topic but I just wanted to share my experience with this power supply. I've owned it for almost 10 years now with moderate usage (daily, but no OC). Had to replace the fan and the OST RLX series caps (the blue ones), which failed on me twice (one cap was bloated, the other one was bad but didn't show visual signs).

I read somewhere in the forum that these blue OSTs were crap, and I can confirm I had two failures. Of course I've been using them for a long time, but still...

I replaced the first one with Nippon Chemicon KY series (the only good ones I could find, general purpose but still rather low-ESR), and the second one with a new RLS series I had around (I hope it won't fail at least in a couple of years). Probably not the best recap but it's been working well.

This PS also sports additional OSTs RLSes in the outputs which I preemptively replaced with Rubycon MCZs.

[PeteS in CA]

Actually, NCC KY series are low impedance, high ripple current parts, probably a good choice. As for the Rubycon MCZ, that might be "too good", and it might not be great in a P/S. If I recall correctly, it's an ultra-low impedance part, and that could affect the stability of the control loop. Also, the water-based electrolytes in ultra-low impedance parts don't do well in hot environments, which the output sides of P/Ss tend to be (hot rectifiers, hot output inductors, and an output harness that impedes airflow).

[Behemot]

I have a feeling that those ostors are ultra-low ESR, Seasonics puts few of them in their OEM units for some reason.

[rsuga]

Originally Posted by PeteS in CA

Actually, NCC KY series are low impedance, high ripple current parts, probably a good choice. As for the Rubycon MCZ, that might be "too good", and it might not be great in a P/S. If I recall correctly, it's an ultra-low impedance part, and that could affect the stability of the control loop. Also, the water-based electrolytes in ultra-low impedance parts don't do well in hot environments, which the output sides of P/Ss tend to be (hot rectifiers, hot output inductors, and an output harness that impedes airflow).

Many thanks for the feedback, I was not aware of these potential issues w/ ultra-low ESR caps in SMPS, and it does make a lot of sense. These RLXs are indeed ultra-low ESRs.

I'll look into removing the MCZs in the upcoming months then. I'll see if I can find KZEs or KZHs around, would those be better replacements? Thanks again.

[sam_sam_sam]

KZE are available but not in all UF values I will use KZE or KY or the automotive type of LXZ and LXY and had no issues using any of these series in switching power supply

[Behemot]

yo ignoring me post for what reason?

[rsuga]

Originally Posted by Behemot

yo ignoring me post for what reason?

In my previous post I replied I confirmed the RLXs were ultra-low esrs, I just didn't quote you as I replying to a previous message.

Appreciate your and Sam's input on this. Thanks again.

[Behemot]

so why exactly yo want to replace anything when its working there in milions of units for over a decade now, FROM THE FAB? if those MCZs don't already have 12 years of use on them, I see no reason to replace anything

[rsuga]

Originally Posted by Behemot

so why exactly yo want to replace anything when its working there in milions of units for over a decade now, FROM THE FAB? if those MCZs don't already have 12 years of use on them, I see no reason to replace anything

If you check my original post above, you'll see the original ones are not MCZs but stock OST RLSes w/ 10+ years which I replaced preemtively (w/ the MCZs) together with the two failed OST RLX caps (the blue ones).

What PeteS in CA conveyed makes a lot of sense (ultra low ESRs where we had low ESRs, water-based electrolytes), so that's why I mentioned I was considering replacing the MCZs again sometime in the future.

Tx.