Corsair CX400W 5vsb goes into safety loop

[Per Hansson]

Re: Corsair CX400W 5vsb goes into safety loop

interesting, never seen a ceramic cap open before.
i didnt know they had a "core", i thought they were layered.

The layers are so thin and close together that they aren't very visible in a picture like that. I've seen the small value high voltage caps cracked open (huge case sizes like 4040 just for the creepage distance), and those do have clearly visible layers.

Yes exactly, I tried my best but even with my EOS 40D DSLR and the Canon 100mm F2.8 Macro lens this is the best I could do, it is after all a tiiiiny SMD part

It looks like a MLCC terminal thermal crack but it includes the electrodes as well. Seems to be from a bad soldering process?
Gideon MLCC Failure Analysis also see SEM Lab Capacitor Failure Analysis

Thank you for those links, yet another thing to keep in mind when repairing electronics!

[PeteS in CA]

Re: Corsair CX400W 5vsb goes into safety loop

The outer surface of an MLCC is a protective insulator.

Non-polymer-termination MLCCs don't like PCB flexure, the larger sizes (>0805) especially.

[lti]

Re: Corsair CX400W 5vsb goes into safety loop

interesting, never seen a ceramic cap open before.
i didnt know they had a "core", i thought they were layered.

The layers are so thin and close together that they aren't very visible in a picture like that. I've seen the small value high voltage caps cracked open (huge case sizes like 4040 just for the creepage distance), and those do have clearly visible layers.

[redwire]

Re: Corsair CX400W 5vsb goes into safety loop

It looks like a MLCC terminal thermal crack but it includes the electrodes as well. Seems to be from a bad soldering process?
Gideon MLCC Failure Analysis also see SEM Lab Capacitor Failure Analysis

[stj]

Re: Corsair CX400W 5vsb goes into safety loop

interesting, never seen a ceramic cap open before.
i didnt know they had a "core", i thought they were layered.

[Per Hansson]

Re: Corsair CX400W 5vsb goes into safety loop

The Corsair CX400 lives again!
I did a cursory Google search and found this post on eevblog:
https://www.eevblog.com/forum/repair...uld-i-do-next/

In it user JeanF describes how he found that ceramic capacitor C107 had gone open circuit, well the exact same fault exists in mine, it has actually cracked!


I mentioned how mine did not work with a 5VSB transformer from another unit:

I found a transformer with at least the same dimensions and similar naming: VEE19FRC3
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.

Actually my hunch was spot-on:
I did have the polarity of the cables reversed, I had to switch polarity of the AUX and 5v output winding and then it works!
(I guess I could also have just switched polarity of the mains input side and it would have had the same effect).

I found a transformer on Mouser that would have been a nice fit, I thought I ordered it but by mistake I had replaced it with another one in my shopping cart so I guess it will just have to live with this upside down transformer
I have tested it up to the rated 2.5A which is actually overloading that transformer a bit (it's rated at 2 amps) but it works fine!

[Behemot]

Re: Corsair CX400W 5vsb goes into safety loop

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.

[Per Hansson]

Re: Corsair CX400W 5vsb goes into safety loop

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

I found a transformer with at least the same dimensions and similar naming: VEE19FRC3
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...

[stj]

Re: Corsair CX400W 5vsb goes into safety loop

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]

Re: Corsair CX400W 5vsb goes into safety loop

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

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.

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...

[budm]

Re: Corsair CX400W 5vsb goes into safety loop

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.

[fzabkar]

Re: Corsair CX400W 5vsb goes into safety loop

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

[Behemot]

Re: Corsair CX400W 5vsb goes into safety loop

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.

[stj]

Re: Corsair CX400W 5vsb goes into safety loop

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.

[Per Hansson]

Re: Corsair CX400W 5vsb goes into safety loop

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]

Re: Corsair CX400W 5vsb goes into safety loop

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]

Re: Corsair CX400W 5vsb goes into safety loop

Ok, it serves another purpose too, during startup the FSQ0165 has an internal switch that takes power from the bulk capacitor and charges the VCC voltage up to 12v.
If this where to fail internally I guess we would be conducting 325VDC here so then it works as a safety device for that as well, though there is a resistor on this side too.

In any case when that is done the switch closes and the device is powered from the transformer.
But seeing as this is high frequency pulsed DC I can't tell you what the voltage is on the other side of the diode (D103) because my meters can't get a reliable reading at this frequency.
But obviously since we have a stable supply after the diode it's somewhere in the range of 20V
My UNI-T meter says it's around 0.2 > 0.5Mhz and the voltage varies depending on load, but as I said it's not a reliable reading.
E.g it can sometimes show 5.7v which is completely impossible since we have a stable ~17VDC output after the diode depending on load.
And my Fluke meter is not able to show anything on either AC or DC so it's similar to my experience in this thread with these meters.

[stj]

Re: Corsair CX400W 5vsb goes into safety loop

if there is a resistor between the source and zener it wont protect the chip.
the zener will conduct, but because of the resistor it wont produce enough of a load to shut the source down.
so it will just keep conducting till it burns out.

if it was a safety device it would drive the base of an scr to short the supply - a crowbar circuit.

when you find one after a resistor it's often intended as a dirt cheap voltage regulation circuit.

so what is the source of the original supply voltage?

[Per Hansson]

Re: Corsair CX400W 5vsb goes into safety loop

stj: no the zener is a protection device.
The Zener will only conduct if the voltage crosses the breakdown voltage, which most likely is around 18v.
Thus protecting the FSQ0165 from too high a voltage (it's rated for max 20v on the VCC pin)

I have attached an annoted version of my picture above, it's the closest thing to a schematic so far
The two diodes in the top: D102 & D103 are marked "A1 W73" on their casings.

[CapLeaker]

Re: Corsair CX400W 5vsb goes into safety loop

Had a PSU a while back that would work for a while, then shut down. One of the voltage rails was jumping up and down after running a while, then shut off. Traced it to a couple of inductors that I had to desolder, take out, clean the through hole and resolder it. Works fine as kinds now. I finally found the problem by watching the voltage rails and using my hot air soldering station, heating up the inductors.