Switching PSU noise on +12V for CPU

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Look if you don't want to respond, you don't need to respond. No sense in personal attacks which are absolutely the most useless posts around.

In any case, to reduce a counterfeiter's costs, one would expect to stick with one large lot and not actually mix them. Or at least have enough of them such that they are very uniform to any one seller.

This is not as uniform as I expected, when I first looked at these they appeared mostly the same (I did notice one anomaly the first pass), until the closer inspection now I see even more within the same batch.

Once again I expected these to at least be close to spec and not blow up in 10 minutes; 10 weeks or 10 months, maybe. After all Dell did not see their computers blow up in 10 minutes else it would have been caught in burn-in.

[kaboom]

Re: Switching PSU noise on +12V for CPU

You've been on BCN since 11/08/2012 and you're just figuring that out?!

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

OH FUN!!!

After about 8 hours, the cap that I stuck on my Sencore decreased to 1300µA leakage... Voltage went up to 13V...

BUT it BLOATED!!! It'll explode any time now!

This is NOT a 16V cap!

And fun... I just noticed these fake Nichicons that I have, they're all sorts of different capacitors from different manufacturers. Looks like the counterfeiter used caps from all companies, so you never know who made that counterfeit. Will have to setup another thread...

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

I hooked up one of these fake caps to my Sencore with 15V reform voltage. Currently it's leaking at 2.8mA, so at least it seems a bit lower than when I was testing with my bench psu. Measuring the voltage with a DMM it looks the Sencore is at 11.8V, so perhaps it hasn't gotten up to the voltage where it was leaking really badly.

The only "good" think is that this cap does read 3300uF±20% at 3500uF... but the voltage rating is really wrong.

Oh BTW, the fake cap took less than 10 minutes of bias at 12V to vent. I pity whoever actually used these as 12V filter caps...

[Wester547]

Re: Switching PSU noise on +12V for CPU

16v is too low for a 12v line - even if a few people will now start flaming me over saying it.
also, if that cap has been sitting for over a year it may have started to depolarize.

i had that the other day, dug out a working board that i stored a couple of years back,
powered it up - BANG - fucking teapo 6.3v cap on the 5v rail!!
replaced the bitch and a matching one with a pair of 16v rubycon's

The Teapo capacitor likely bulged because it's crap and no other reason. Teapo capacitors are sometimes known to outgas without ever having _any_ bias applied to their plates (in storage). It does hold true that capacitors from crap brands (nevermind counterfeit capacitors) are more likely to be overrated, not just in terms of voltage and capacitance but in terms of ripple current in the datasheets (which in and of themselves tend to be amuck with sloppiness and inconsistent values).

And IMHO, if 16V was really too low for the +12V input (or output), for wet electrolytics, expedited failures, even from good brands and series, would be more commonplace. Leakage current does augment as you approach the rated voltage, and that in turn causes the consumption of electrolyte to rise so as to correct defects (even those minor) in the oxide layer (reforming). I like the fact that those recent HMs survived voltage torture testing. I wonder if any KZG could survive and brave the same challenge?

[kaboom]

Re: Switching PSU noise on +12V for CPU

when I set my bench PSU to about 14V I see about 300mA leakage on a 16V cap. This is NOT right...

Thinking outside the box, it makes perfect sense when you consider those are fake caps...

Not 16V rated at all.


FWIW, I have "torture tested" several Nichicons out of various equipment I junked. I applied 18V to several PW, VR, and HM 16V caps, from 100u to 4700u, and after a few minutes, leakage in most cases was below 10mA, with the 4700u/16V VR ultimately withstanding 20V with less than a mA of leakage.

Again, these were used caps from junk equipment.

Legitimate "16V" caps are usually formed to withstand 20V; the old datasheets would list these as 16V rated/20V surge.

As for the fake caps, they'll have whatever printed on their sleeve that looks or "feels" good, depending on their intended use (mobo, SMPS, etc).

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Hmm...Since my Sencore also has a "reform" function, I wonder what it will do with these leaky caps....
I need to stick it in a blast chamber and see what happens when I let it reform for a while. This cap shouldn't be all that old...

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Weird. I cannot find 16V caps on this Foxconn M/B, maybe it does not have prefiltering and depends on the PSU to do all the filtering?

I also checked the ATX24 power plug. Holy crap, I see 600mV droops on this wire that aren't visible on other wires.

And those fake Nichicons. I tried repeatedly rapidly manually charging/shorting one of them, yes the cap starts getting warm. Maybe expected, but when I set my bench PSU to about 14V I see about 300mA leakage on a 16V cap. This is NOT right...

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Leakage also rises with how close it is to their rated voltage...

[stj]

Re: Switching PSU noise on +12V for CPU

leakage rises with age.

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Anyone have leakage meters? The caps that I have, the "good" ones - even used ones from top end manufacturers, barely leak at all at their rated voltage. It's these shitty fakes that aren't close. I think these caps are really 10V and not 16V, and no wonder why they blew up at 12V (though I did not expect them to behave as they did... thought they would last at least for a little while...)

[stj]

Re: Switching PSU noise on +12V for CPU

16v is too low for a 12v line - even if a few people will now start flaming me over saying it.
also, if that cap has been sitting for over a year it may have started to depolarize.

i had that the other day, dug out a working board that i stored a couple of years back,
powered it up - BANG - fucking teapo 6.3v cap on the 5v rail!!
replaced the bitch and a matching one with a pair of 16v rubycon's

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Weasel: FAKE FAKE FAKE

FAKE NICHICON
Before popping: capacitance: 3500uF
ESR = 0 (cannot measure, my ESR meter resolution doesn't go that low)
Leakage at _10_ volts: 75 microamps

After popping: capacitance: 2100uF
ESR = 0.9 ohms
Leakage at _10_ volts: 75 microamps

Testing leakage at 15 volts, my Sencore says No Can Do, Leaks Too Much.

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Right, as said earlier, I was wondering if it was OK, and some of this could possibly be wire related. The probe point is on the upper side of the connector, so the board 2x2 connector resistance is not part of the circuit to the scope. I should try more machines or find another PSU to compare with. I guess it does make sense as the MB should have a buck supply that yanks on the rail for a fraction of a cycle, but wonder where the cap in question should be (mb, psu?) Or is it just the wire?

I don't recall this PSU as a dual rail 12V (which could also explain things, alas it's not) but what bothers me is that if these circuits are truly hooked up to the same tap, the only additional series resistance to the CPU power plug is those two 1ft pieces of wire to the m/b, else all outputs should look like the same especially since they're unloaded.

[EDIT]
OK, I see one of my dead Asus motherboards actually has a 16V cap on it, assuming that is the onboard 12V filter for the 2x2. Now I need to look for the same for the Foxconn which is the board in question. Still surprised it will show on the 2x2 top pin but not on the other unloaded taps of the PSU.

[EDIT 2]
You know what, fsck this. I'll stick in some caps on the top of the 2x2 connector and see if the behavior changes... ha...

[EDIT 3]
I stuck in a phony Nichicon 3300uF 16V cap in parallel with the 12V 2x2 (stuck it into the top of the connector and forced it in). Got the ripple down to ~100mV total. The funny thing is that this is a phony and while I was experimenting...

POP! Goes the Weasel!

This is the first time I saw a cap pop. I don't even think I connected it backwards, it's correct according to the sleeve and the wire lengths (shorter wire is usually GND). Alas it popped, steam wheezed out. Dead Fake Cap, nothing lost, experimental data gained.

[kaboom]

Re: Switching PSU noise on +12V for CPU

if you see something on the board but not at the psu, either your wires arent up to the job or you have a bad joint or poor/burned crimp terminal

No, "if you see something on the board but not at the psu, the load is backfeeding ripple into the caps (and feedback ckt if PSU's caps are marginal) in the originating supply."

Remember, certain video cards were supposedly "incompatible" with certain power supplies, whereby a "mismatch" made those vulnerable SMPSes hunt around and shutdown when the VGA card started taking load and backfeeding its ripple into the PSU.

Regardless, allwire has resistance, and the caps at the supply, while they are shunting the suckouts to a degree (seen on unloaded molex plux), the caps on the board are supposed to provide current to "fill in" those suck outs.

Even more with the choke most mobos have between the incoming +12 and their bank of caps before the high side devices.

And since all wire has resistance, you'll still measure more ripple at a load such as a CPU buck converter, unless extreme filtering is provided at the board; again, it is not the purpose of the caps in the SMPS to "anchor" something at the down at the load.

The ripple current loop at the downstream converter is commutated/shunted by those caps on the board! If increasing wire size back to the source reduces ripple voltage present at the load, then the caps at the load are marginal. Even w/o burned terminals- all wire has resistance.

[stj]

Re: Switching PSU noise on +12V for CPU

if you see something on the board but not at the psu, either your wires arent up to the job or you have a bad joint or poor/burned crimp terminal

[kaboom]

Re: Switching PSU noise on +12V for CPU

i would say the deep drops are a lack of ripple-handling,

No, they don't appear at the cap in the supply, which the unloaded disk drive connector "jumper wire" allows the scope to see.

[stj]

Re: Switching PSU noise on +12V for CPU

i would say the deep drops are a lack of ripple-handling, something very few meters can check.
the small peaks may be an esr issue.

mobo caps are probably done though or the board wouldnt show load peaks that sharp

[kaboom]

Re: Switching PSU noise on +12V for CPU

Maybe the input caps on that +12 to vcore converter have high ESR, and when the highside devices come on, you get the suck outs.


If the power supply had bad caps, you'd see the same, or more, noise on that unloaded molex. Did this ever occur to you?

[eccerr0r]

Re: Switching PSU noise on +12V for CPU

Well one thing is the ripple generated by the PSU, the other thing is ripple caused by load. The really thin downward spikes are load caused, how that should be accounted for I'm not sure.

I tried another PSU and it wouldn't boot. But this PSU was questionable to begin with (it has a 20-pin ATX where the m/b has a 24). Plus it was a swapout since it couldn't power a P4 anymore.

The ripple at the power connector really has no bearing on the ripple seen by the CPU - as the onboard switching regulator will attenuate the noise even more... The ripple on the 1x4 molex 12V (trace ch2) is just about 100mV so it's getting close to the limit.

The unfortunate problem is that the original PSU is a custom one as it's a low profile microatx case. Cap replacement is my only option though I'm not sure even if they are replaced, whether it will be clean...or is it the motherboard caps that need to be replaced (not sure if there are any significant 12V-capable caps on the motherboard... most seem to be too low for 12V...)