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Old 23rd February 2010, 04:50 PM   #11
llwhtt is offline llwhtt  United States
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I started my electronics career in 1974 and have yet to replace a bad "computer grade" capacitor. I have milk crates full of them that I pick up when I find a good deal at surplus stores. If there is no physical damage I don't think twice about buying them. They are usually only a couple of bucks apiece so you can get a couple of amps worth for the price of a new one. Just reform them before you use them if are worried.

Craig
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Old 23rd February 2010, 05:08 PM   #12
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Default Electrolytic caps

I've replaced a lot of 440 VAC motor drives under 5 years old where the electrolytic caps leaked out into the bottom of the box, then the drive quit working on cold mornings. Quality brand motor drives usually last more like 10 years before the caps explode. Half the electronic equipment I replaced in the factory had visible electrolytic cap problems. I just replaced every electrolytic cap in my new 1968 Hammond organ, it has quadrupled the volume, lowered hum by half, increased the high frequencies, and restored function to the percussion circuit that was inaudible when bought. Hammonds and Leslies made in the 50's are known to explode the bottom out of can caps. Spend your money where you want, I'm buying new caps from a distributor that puts a discount symbol next to the line if they are over 18 months old. Notice new caps come in various lives, 500 hours to 10000 hours. I pay extra for the ones labled to last thousands of hours. When I do so, I receive the brands and appearance that mostly I saw in the long life motor drives.
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Old 23rd February 2010, 07:14 PM   #13
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Quote:
Originally Posted by pforeman View Post
Not quite sure if I got this part right.
Applying voltage reforms caps.
So regular use will regularly reform your caps.

wow what a long paper
thanks,
Paul
You got it right. This thread is quite timely to me. I was toying with the idea of starting just such a thread. There is no shortage of people that are sure electrolytic caps go bad. I tend to disagree, and it was nice to find that paper seems to confirm what I believe. It is also nice to hear from others that feel the way I do.
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Old 23rd February 2010, 07:21 PM   #14
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Originally Posted by Steve Dunlap View Post
You got it right. This thread is quite timely to me. I was toying with the idea of starting just such a thread. There is no shortage of people that are sure electrolytic caps go bad. I tend to disagree, and it was nice to find that paper seems to confirm what I believe. It is also nice to hear from others that feel the way I do.
In the amplifiers serviced here we are certain many of the electrolytic caps go bad from testing those very caps. Actually, ripple current seems to kill most of them. 10 years of service when the amp is used almost daily we find dead electrolytic caps.
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Old 23rd February 2010, 08:11 PM   #15
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Originally Posted by sumaudioguy View Post
In the amplifiers serviced here we are certain many of the electrolytic caps go bad from testing those very caps. Actually, ripple current seems to kill most of them. 10 years of service when the amp is used almost daily we find dead electrolytic caps.
I only serviced equipment for friends the last several years I could work, but some of that was over 40 years old. I have only found one bad electrolytic cap. I'm sure I haven't seen as many pieces of service gear as you, but I do have a capacitor analyzer that checks for value, leakage and ESR. I don't doubt that you have seen many bad caps. It sounds like you service electronics, so you see a disproportionately large sample of equipment that has failed to operate properly. As sakis pointed out, some brands or models have more problems than others. I suspect that is primarily because the manufacturer cut cost by selecting electrolytic caps that weren't of sufficiently high quality. I believe you are correct about ripple current and the resulting temperature rise being the cause for failures. I also believe that proper selection of capacitors will prevent this.
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Old 23rd February 2010, 08:56 PM   #16
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I believe you are correct about ripple current and the resulting temperature rise being the cause for failures.
I tend to agree with you Steve and sumaudioguy. Actually, caps in audio have an easy life when compared to those used in photoflash.

It's not uncommon to blow caps in some of these high powered flash generators, especially those fast charge "transformerless" types. Caps are charged to 800V to 1,000V directly from the Mains and dumped instantaneously when the camera is fired. When a 3,000 joules pack blows, its pretty dramatic.
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Old 23rd February 2010, 09:29 PM   #17
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Originally Posted by Steve Dunlap View Post
I only serviced equipment for friends the last several years I could work, but some of that was over 40 years old. I have only found one bad electrolytic cap. I'm sure I haven't seen as many pieces of service gear as you, but I do have a capacitor analyzer that checks for value, leakage and ESR. I don't doubt that you have seen many bad caps. It sounds like you service electronics, so you see a disproportionately large sample of equipment that has failed to operate properly. As sakis pointed out, some brands or models have more problems than others. I suspect that is primarily because the manufacturer cut cost by selecting electrolytic caps that weren't of sufficiently high quality. I believe you are correct about ripple current and the resulting temperature rise being the cause for failures. I also believe that proper selection of capacitors will prevent this.
ha ha ha ha ...Steve ...i dont know what you are doing these days but if you pop up in my company you will need to second think this .....

please notice we never service equipment older than 30 years ...actually we hardly ever repair machines that are capacitor coupled in the output ...

Trust me any brand marantz pioneer nakamichi akai teac and many many other go for a total recaping ...at least all the small ones at this age

we normally service 150 amps a year .... trust me when i go to the parts shop the people look at me with a big smile !!!!
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Old 23rd February 2010, 09:39 PM   #18
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Default rebuilt 1200b scope today

Just rebuilt an HP 1200b scope today and 2 of the main supply caps still tested good. One was far out of spec.

In a rebuild all electrolytic caps are replaced here. Sort of a shotgun approach as we are sure we got the bad ones. The result is good reliability. We like the high temperature 105C or higher and high ripple switching type.

Before someone says something about rebuilding such an old scope and why bother, the answer is two channels of differential inputs with 100V/div sensitivity. 500kHz bandwidth is great for power supply and low noise work.

Last edited by sumaudioguy; 23rd February 2010 at 09:41 PM.
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Old 23rd February 2010, 10:05 PM   #19
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I used to work in service, though not audio. Eventually it drove me crazy (it doesn't show does it?) because I became convinced that everything was junk. Obviously the only things that come through service are the things that don't work. You have to be careful trying to get a good statistical picture from a subset called "broken". OTOH, of things that fail, caps are way high on the list, as are mechanical connections of all sorts. IMO, you have to be careful specifying caps, as ripple current can raise the internal temperature and shorten life dramatically. That 85C number is way easier to reach than most people think, though audio equipment should never stress caps if the designer had a clue. Sadly, I don't think they physically measure ripple current even in most commercial equipment, and that's the only way to be sure of what's happening. Most caps get picked by rule of thumb and sometimes that rule is wrong. I've worked for electronic companies for 35 years and have never seen anybody (except me) measure ripple current in a power supply cap. Go with brand names and measurements. If the cap is properly applied, made well and tests good for all its parameters, it will last for decades.

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Old 24th February 2010, 12:25 PM   #20
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Originally Posted by Conrad Hoffman View Post
I used to work in service, though not audio. Eventually it drove me crazy (it doesn't show does it?) because I became convinced that everything was junk. Obviously the only things that come through service are the things that don't work. You have to be careful trying to get a good statistical picture from a subset called "broken". OTOH, of things that fail, caps are way high on the list, as are mechanical connections of all sorts. IMO, you have to be careful specifying caps, as ripple current can raise the internal temperature and shorten life dramatically. That 85C number is way easier to reach than most people think, though audio equipment should never stress caps if the designer had a clue. Sadly, I don't think they physically measure ripple current even in most commercial equipment, and that's the only way to be sure of what's happening. Most caps get picked by rule of thumb and sometimes that rule is wrong. I've worked for electronic companies for 35 years and have never seen anybody (except me) measure ripple current in a power supply cap. Go with brand names and measurements. If the cap is properly applied, made well and tests good for all its parameters, it will last for decades.

Conrad
Here here. When designing I measure current of every lead of every device including grounds! The only way to know for sure, period.
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