--Silly question time: do capacitors tend to drift in the same direction? And if so, which way? Just got stereo out of the shop and the repair guy said the problem was with the caps..
-- "Steamboat Ed" Haas : Blue Cross socks us Hacking the Trailing Edge! : $23,000/yr!! ...
Depends on what is causing the drift. Temperature is one cause. Some drift positive, some drift negative. Why do you interpret "problem with the caps" as drift? Tom
"steaming great idiot "
** Depends which way the wind blows - f****it. ** No fooling ??... Phil
Capacitors can fail. They lose their capacitance over time and electrolytic can drop significantly. This is probably what you are asking for as it makes the most sense. Capacitance can obvious locally change due to temperature fulgurations and other things but generally it will not cause a circuit to fail or generally even operate erratically(unless it is very poorly designed). But if it is old or uses cheap capacitors, specifically if electrolytics, then the device can fail in any number of ways.
For audio stuff caps tend to be used for two primary purposes. One is power regulation and the other is audio filtering. The filtering caps generally rarely go bad and if they do it is results in a gradual decay of sound quality except when a catastrophic event occurs. The power regulation caps are generally what fail the most and can be due to over voltages and such. They are the large capacitors in the device. Generally they cost up to a few bucks each so if he charged you an arm and a leg then he's probably ripping you off. For example, it could simply have been a fuse and he said it was the caps.
If they were replaced it should be someone easy to tell and generally there are just two to four of these(they will be the largest ones there). It is possible the power stage uses SMPS which reduces cap size and may make it harder to find the.
BTW, a capacitor is basically a battery that works in a similar way but has opposite properties. A capacitor can be charged up or discharged very quickly(battery = slowly) and cannot old a charge as long(a battery can last quite some time). In fact, in some cases capacitors can be used to replace batteries(so called supercaps that can hold a ton of charge). Actually a battery is a type of capacitor that was designed to last longer but at the price of not being able to dump it's electrons as quick.
Example, if you short out a capacitor it will "release" a large number of electrons in almost an instant. Say maybe something like 1 million amps in
1ps(10^-9 seconds). 5ps later it maybe down to 10,000A. 1000ps later it's basically at 0.A batter OTH might be able to put out a few amps for several minutes which will slowly drop off.
Of course I'm just trying to give you some idea as the specific numbers depend on the actual devices used.
Increased ESR is the most common problem.
In general, no they do not change capacitance over time within their tolerance ratings. They all have a tolerance rating with some types are as bad as minus 82% meaning they can lose almost half of their capacitance with time and temperature but still be in range. Others are more tight in tolerance and can be expected to keep their values indefinitely.
Of course any cap or electronic part can go bad and lose capacitance for any number of reasons.
When a repair guys says the problem was with the caps, what does he mean? What caps? A certain cap? Or a whole bunch of them? We really need more information for a definitive answer. I would be wary if more than one cap was found bad. It could happen but you may have been scammed. Some repair guys just "shotgun" a problem replacing everything they can think of, good or bad, in hopes of hitting the problem..
"Bob Eld"
** Utter BOLLOCKS !!Even the poorest quality electros will not lose any capacitance until they reach the end of their useful life.
The percentage tolerance band quoted is FROM NEW !!
But ALL caps drift in value with temperature, some go up and some go down.
Refer to maker's specs for the details.
.... Phil
No, tolerance is a different thing. It's about how close to the stated value it is when it comes from the factory. For some applications, the value doens't matter much, so you can live with a wider tolerance, which at one point meant a cheaper capacitor (I'm not sure how that holds today), while other capacitors need to be very close to the needed value and thus you get a higher tolerance capacitor.
Electrolytics generally have a wide tolerance, which seems to be a reflection of the manufacturing process, but then maybe when they are used most applications (filter and bypass capacitors, audio coupling capacitors) aren't fussy so nobody spends the money for higher tolerance electrolytics on a regular basis.
Some types of capacitors are more likely than others to change value over enough time.
There is also how a a capacitor reacts to temperature, again for a lot of purposes that doesn't matter since the value isn't critical, while for some very specific applications it matters a lot (in which case one picks capacitors that are will vary less with temperature, and even get capacitors that are specifically designed for temperature compensation.
Michael
Sometimes you are interesting and informative and other times...
--Thanks for the useful response! I would guess that the power regulation caps went south as there was a continued tripping of solenoids, disabling the speaker outputs. And yes, it's an older unit: maybe 35 yrs or so now. First failure of this sort so a decent MTBF IMO. The guy didn't charge as much as I had feared so I'm happy with the fix. Also happy to have learned something.
Ack. I guess the real trick is knowing how to detect the fault in so complex a contraption. I took a peek under the hood B4 I took it to the shop and I was totally flummoxed. Not just circuit boards but lotsa wire wrapped stuff. Decided to let an expert work on it! :-)
--Ack; I built a small mass driver once upon a time; used about .5 farad and burned out a few switches in the process, heh. Thanks again
--
"Steamboat Ed" Haas : Blue Cross socks us
Hacking the Trailing Edge! : $23,000/yr!! ...
www.nmpproducts.com
---Decks a-wash in a sea of words---
--Thanks; saved the link. Most helpful!
-- "Steamboat Ed" Haas : Blue Cross socks us Hacking the Trailing Edge! : $23,000/yr!! ...
--It's been a long time since I killfiled anyone but this bozo prompted action. Any more kooks I should look out for over here?
-- "Steamboat Ed" Haas : Blue Cross socks us Hacking the Trailing Edge! : $23,000/yr!! ...
--Aha! Thanks for that; for some reason I had assumed they all fail in the same direction, so to speak.
--Well I know it's one of several ways they fail; Just curious about what/where/when/why, so to speak, as I've heard of the problem from others messing with Stamp circuits, etc. I guess there are several failure modes; it's just a term I've encountered so curiosity got me thinking. Thanks for helpful response!
--
"Steamboat Ed" Haas : Blue Cross socks us
Hacking the Trailing Edge! : $23,000/yr!! ...
www.nmpproducts.com
---Decks a-wash in a sea of words---
I wouldn't killfile Phil. He quite often gives intelligent accurate advice. From time to time he gets like you saw. (Some of us think it's a medication issue.) I always read his responses, if they are the wacky kind I just ignore it.
Regards, Tom
Phil is abrasive and abusive, but he generally knows what he's talking about, and has made many useful contributions to the group.
Why he behaves as he does, I neither know nor care. I have quite a few bozos killfiled, but he is not one. Engineering skill overrides personality, as far as I am concerned.
Leave him out of your killfile, and maybe you'll learn something you didn't already know,
--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
** Did you actually read the f****it OPs absurd question ??
Calling him a "steaming great idiot" was being kind.
..... Phil
This guy:
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Probably electrolytic caps in the power supply. They can dry out over time and lose capacitance and increase ESR.
Film and ceramoc caps are pretty stable over time and change a bit with temperature. Not enough that you could hear any difference.
Do you trust this repair guy?
John
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