Capacitor Mystery

Why don't you simply replace them for new ones of their marked value??? This should not be too complicated...

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Jerry G. =====

I have several of these that measure considerably less than their marked value. I'm thinking that they might be the type of capacitor that uses metallized film, which burns off when it has a dielectric failure. The many burnoffs may cause the capacitance to decrease substantially over time. Could this be the reason for the low measured capacitance?

I've googled and I came up with info on Siemens capacitors at EPCOS, which seems to be the Siemens and Matsushita capacitors, which is how the documents are labeled. But I can't find any info on this model. I would guess that these capacitors are teenagers at least, agewise. I've also looked on Faradnet. Any ideas?

Thanks.

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My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it:

This

You have missed his point entirely. He is not saying that he has problems with failures in a circuit; he is interested in known *why* these devices are failing as they are.

Cheers!

Sir Charles W. Shults III, K. B. B. Xenotech Research

321-206-1840

value??? This

I just go Click, Click! And the whole board pops out of the card cage, I drop it in the trash, and I just insert another card, of which I literally have tons more.

And i'm just interested in the failure mode, why and how this is happening. Many of the others measure something like .872 uF, which is well below the 5% tolerance but still allows the circuit to function. But I'm thinking that the marginal capacitance is causing the audio quality to suffer.

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If you want to investigate the failure mode you might want to build
yourself a zapper, then do a "before and after" test on one (or
several) of the caps;  measure the capacitance, zap the cap to burn
off some of the metalization and then remeasure the capacitance.
Depending on how much metal you remove/displace (or whatever that
self-healing mechanism is) per hit, you may have to zap it a bunch of
times before you get a measureble change in capacitance.

cage,

is

But not only how many times, but how much voltage? It's a 1 uF cap, so it will hold qquite a bit of charge. How do I zap it? Jacob's Ladder? Tesla Coil? Connect it to the primary of a 120VAC to 6VAC at a couple amps transformer, and then arc the 6V winding to a nice, high current power suource?

If the zapping isn't strong enough, the change after many zaps might be nearly zero. if it's too strong, the smoke might come out. Or something else might come out. Scary thought.

Electrolytic capacitors have a life span, under good conditions, of 5 years.

You're lucky to have a few teenagers amongst those you have.

The fact is that this is the basis of consumer electronics life-period. (life-span)

Any devices life span is dictated by the life expectancy of it's comp>

Dunno about that! I have a Roberts Tape Recorder from the 60's that still works fine. Never replaced a component in it. Were the old components more robust than the current crop?

Al

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There's never enough time to do it right the first time.......

Capacitors take a beating in modern equipment ( mid 1980's and now). I would say when they started using cap's in switching supplies and in pulse formation (Vertical and Horizontal sweep) and flyback derived DC voltages. Reducing size of equipment and improper cooling (cheap fans) doesn't help either. Will the short product cycles eventually burn the Manufacturers ? Products today are not as reliable as they once were, they don't have to be. People accept the junk products of today, they accept having to install continuous software upgrades as a way of life. Years ago if you had to constantly upgrade to keep going, people would find another way. My opinion only...

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*************************************************** "We ought always to know precisely why a given job is done in a particular way, and why it is done at all, and why it can't be done more efficiently, if it must be done at all."-- T.J.Watson

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years.

It's supposed to last a lot longer than 5 years because it's not an electrolytic.

My own experience says that electrolytics last a lot longer than 5 years as long as t hey don't get hot. The hotter they get, t he shorter thay last. So if you have an old toob amp with the 'lytics next to a toob, then good luck. That commonly happened with the rectifier. But nowadays you get get a solid state substitute for the 6X4, 5U4 or whatever.

[snip]

Yeah right. Don't tell my vintage audio equipment. 30+ years and counting. And btw, sensible manufacturers give you a formula to calculate expected lifetime. I have never seen one state an explicit number of years.

Michael

Keep in mind, though, that there's a difference between the expected IN-SERVICE lifetime for electrolytics, vs. their shelf life. If stored for long periods with no voltage applied, the dielectric layer (the really, really thin layer of aluminum oxide formed on the foil) may degrade, often to the point of making the cap very likely to fail soon after being placed in service. If the cap is actually IN service, though, the regular application of voltage across the thing keeps it healthy. (Remember that the dielectric layer is produced by the application of a "forming" voltage as part of the manufacturing process in the first place.)

This, of course, is a completely separate concern than the possibility of the electrolyte drying up due to a less-than-perfect seal...

Bob M.

The statements above illustrate why it is so important to state the conditions under which the items under discussion are used. Both answers are correct, if the conditions warrent them.

BTW, I think I once read that the Spitfire engines used during the Battle of Britain had to be overhauled after 10 hours of flight. And that was because they were being operated in an overrated condition so they could produce the extra horsepower needed for the air battles. The NAZI planes could not be overrated as they had much further to fly.

Al

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There's never enough time to do it right the first time.......

5

counting.

expected

It used to be that serious audiophile gear used good quality 'lytics such as Western Electric caps. Those were the gray colored ones that were made for communications equipment that was designed to last for 30 years. I think McIntosh used those, and maybe some other makers as well.

I have a few HP power supplies that are over 30 years old, and still going strong with the original caps in them. So never say never.