A bulge necessarily equals a bad capacitor?

**linuxguru** · 11-11-2005, 08:53 AM

Re: A bulge necessarily equals a bad capacitor?

A domed/cracked top is always indicative of a capacitor that will fail. However, very slight bulges are sometimes present even in premium capacitors at the time of manufacture - I have a bunch of new Panasonic/Matsushita caps that have a tiny, barely visible bulge.

**Chris1992** · 11-11-2005, 01:27 PM

Re: A bulge necessarily equals a bad capacitor?

And what capacitors are they? Intel boards are famous for using almost always good caps.

**willawake** · 11-11-2005, 02:29 PM

Re: A bulge necessarily equals a bad capacitor?

the only likely candidates for failure on a Intel D865PERL would be the nichicon HN(M) or HM(M) series or in some cases the little yellow fujitsu caps (have an F symbol on them) can cause a problem. the rest of the caps would be rubycon, other nichicon series or united chemicon which are good.

for your installation issues, i have no idea, not cap related though. perhaps a different bios might have helped? my D875PBZLK doesnt supply enough voltage to the hyperx ram to run it at the proper agressive settings. they implemented vdimm adjust in a later version of the board

anyway check for HN HM and tell us which cap is bulging. a pic would be nice.

**Fatal0E** · 11-11-2005, 08:58 PM

Re: A bulge necessarily equals a bad capacitor?

Built many security camera DVR systems with this board, and the 845epil, they are all coming back in with blown nichicon HNN caps, tall skinny ones next to the cpu. Intel fixes them for free with chemicon and oscon caps.

**einhverfr** · 11-17-2005, 01:19 PM

Re: A bulge necessarily equals a bad capacitor?

Just for the record in order to help people who may read this later.

A domed/bulging capacitor always indicates a capacitor that needs to be replaced. And this may occur for reasons other than manufacturing flaws.

Electrolytic capacitors have one issue as a group. They have a liquid in them (the electrolyte mixture) which can boil when the cap overheates. To prevent uncontroled explosions, these caps are "vented" on the top usually with stamped lines in the aluminum foil casing. This means that this area will be the first to fail under pressure. So bulging capacitors indicate ones that are overheating under current use. They should be replaced.

Most of the discussion on these forums centers around bad electrolyte mixtures that boil at low temperatures (within the expected operating temperature of the cap). However, all electrolytic capacitors can fail/overheat if voltages are reversed, if a voltage spike occurs, or if other heating problems are present. So the fact that these are otherwise good brands of caps provides no guarantee that an individual cap will not fail. I would therefore suggest that if the cap is overheating and is an otherwise known good brand that you might want to consider replacing it and monitoring it, and if the second one starts to fail, replace your motherboard before something bad happens.

**Per Hansson** · 11-27-2005, 11:59 AM

Re: A bulge necessarily equals a bad capacitor?

Was installing a NIC in a Intel D865PERL board, saw two bad Nichicon HN(M) caps between the CPU and RAM... No pics because I was unable to take a good pic with his digicam...

http://www.intel.com/cd/channel/rese...tes/193414.htm

**arneson** · 11-27-2005, 12:28 PM

Re: A bulge necessarily equals a bad capacitor?

Originally posted by einhverfr

the fact that these are otherwise good brands of caps provides no guarantee that an individual cap will not fail. I would therefore suggest that if the cap is overheating and is an otherwise known good brand that you might want to consider replacing it and monitoring it, and if the second one starts to fail, replace your motherboard before something bad happens.

This is good advice but the monitoring may be difficult for a machine that's not in your possesion.
Very good post, you kind of summed up my feelings nicely.

**willawake** · 11-27-2005, 02:20 PM

Re: A bulge necessarily equals a bad capacitor?

Was installing a NIC in a Intel D865PERL board, saw two bad Nichicon HN(M) caps between the CPU and RAM...

what was wrong with the onboard nic?

anyway you wanna get RMA on the board. hopefully you will get back a late revision which will be kickass.

i wish my D875PBZLK had badcaps to get me a late revision

**willawake** · 11-27-2005, 02:23 PM

Re: A bulge necessarily equals a bad capacitor?

They have a liquid in them (the electrolyte mixture) which can boil when the cap overheates

nobody has any comments on that?

**PeteS in CA** · 11-27-2005, 07:25 PM

Re: A bulge necessarily equals a bad capacitor?

nobody has any comments on that?

[Basso profundo]You rang?[/Basso profundo] Hmmm ... well, if you simply heat a lytic, not connected to a circuit, they start to swell at around 140C-150C (ambient, case, and core temp). When I torture caps, their core may reach that temp when I start to see swelling, but I suspect another mechanism may be at work - in my tests and in the MBs these forums focus on. I think it is very likely that the ripple current (in my tests and on the MBs) is causing the cathode foil to be formed, which generates hydrogen gas and can cause swelling and venting.

While I agree that the electrolyte is a vulnerability in a lytic cap, that electrolyte is also the true cathode of the capacitor (the cathode foil simply makes the electrical connection to the outside world possible). As such, the electrolyte is necessary for there to be capacitance, and the electrolyte also conducts the ripple current.

**linuxguru** · 11-27-2005, 09:00 PM

Re: A bulge necessarily equals a bad capacitor?

> I think it is very likely that the ripple current (in my tests and on the MBs) is causing the cathode foil to be formed, which generates hydrogen gas and can cause swelling and venting.

There may be multiple mechanisms at work:

1) Direct electrolysis giving rise to H2 that is not fully neutralised by (possibly inadequate or missing) depolarizers - this is directly related to high ripple current.

2) Basic pH of faulty electrolytes directly attacking the aluminium foil due to the failure of Aluminium oxide barrier layers - this can explain the failure of some caps like YEC that have never been in-circuit, leave alone powered up.

3) Impure foil containing 2.5% copper that causes local galvanic action and foil corrosion, leading to failure (this is related to 2. above, in that it can happen without any voltage applied to the electrodes).

4) Overheating due to ripple current and/or proximity to the CPU that causes trapped moisture to evaporate to steam - this is probably the dominant failure mode in the small yellow Fujitsu polymer SPAs on the Intel motherboards (this could also be considered to be a design flaw by Intel, rather than a quality issue in the capacitors).

The chemistry is fairly complex as numerous materials are found in a modern electrolytic, so there are probably additional mechanisms at work. As a general rule, if the rate at which it fails increases exponentially with a rise in temperature, there is a chemical (Arhenius) mechanism in play; if it increases linearly or not at all with temperature, there is a pure physical mechanism (like phase change or dissolution) at play.

Both kinds of mechanisms are always at work - but in a good capacitor, the rate of reaction is vanishingly small over the entire range of conditions it is specified for, giving a long lifetime.

**arneson** · 11-27-2005, 10:47 PM

Re: A bulge necessarily equals a bad capacitor?

Sounds like a description of my Liver, which I hope will give long life.

**willawake** · 11-28-2005, 03:10 AM

Re: A bulge necessarily equals a bad capacitor?

Sounds like a description of my Liver, which I hope will give long life.

did you get extended warranty?

nice post by linuxguru btw

A bulge necessarily equals a bad capacitor?

A bulge necessarily equals a bad capacitor?

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