Telltale signs of failing electrolytic capacitors.

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I think a lot of the controversy is caused by the large variations in component quality and operating conditions along with sheer pot luck, along with at least two different failure modes (capacitance reduction and high ESR vs. excessive leakage + shorting). On the one hand, people have occasionally found 1960s era can-type filter capacitors that were perfectly fine (but probably not in AA5s or most guitar amps), on the other hand a PA amplifier ridden hard may well be overdue for recapping after 20 years, and I'm not even talking about SMPS in toasty environments and/or with dodgy caps.

Ultimately, you can only check - or at least spot-check - capacitance, ESR and leakage to know for sure whether the parts are still good. (Which, mind you, may be nearly as much work as changing them.) Cap manufacturer and series also tend to give some clues. Appropriate derating (or lack thereof) can be another clue, and applied voltage in general - any low-voltage part that has only ever seen millivolts of DC in 40 years is probably a leaky mess at this point.
 
I have two old radios from the 1960s, of similar design except one has a wooden case and the other a plastic case. The electrolytic which needs replacing is the one across the FM discriminator. This always fails after a few decades use. Why? Because it is above the chassis right next to the output valve (and not far from the rectifier) so it get heated and eventually dries out. That is an example of what I meant by 'abuse'.
 
I remember learning electronics on a course in around 1980.
We all had a small amplifier to build up.
It had a couple of electrolytic caps on the power rails.
During the afternoon then would be bang after bang and caps flying around.
Only a couple of the 12 students didnt blow the caps up.
There would be a bang then a big cheer would go up.

Caps can go various ways.
Some lose capacitance as they grow older.
Some go short and blow fuses.
Some swell up.
Some leak.
 
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those were the days.....this is a nice forum where all they talk about are the bad caps.....Badcaps Forums - Salvation For Your Electronics!

many many years ago, i made a living out of replacing bad caps in computer mother boards, typical board can have 5 or more of those bloated and failed caps....symptoms were, not able to POST, so the computer wont load windows....
replacing all bloated caps cured the problem....where did i get my replacement caps? from atx psu sold at surplus stores....
there was time, when this problem was prevalent, when the aqueous liquids used in the manufacture of ecaps were of poor quality....i even repaired video cards with the same problems....it was good business, i made some food money.....
 
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Smell is another tell tale sign. I was repairing a Mark Levinson cd player with a bunch of bad caps. They weren't bulged but the voltage rail was being dragged down. Finally I lifted one and a bit of electrolyte had leaked and created a carbon short that was hidden. Every 100uf 25v cap was bad and cd player was from the 1990s.
 
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At my service shop back in the 1990's, early 2000's, there was a rash of Mitsubishi large screen tvs going bad.
It seems they all had hoardes of bad capacitors throughout the set leaking like mad.
I remember the "fishy smell" they made when being unsoldered from the corroded boards.
 
My father’s collection of late valve and early solid state era hi fi and test equipment turned me into a capacitor skeptic.

I tend to remove the caps in an unknown piece of equipment, test them as throughly as I can, compare them to a new cap measured with the same equipment and replace them if they measure appreciably worse.

It does seem to depend on the equipment and how it is used, there are axial Phillips caps in some of my line level stuff that measure better than modern Nichicon replacements and on the other end of the spectrum the main rail caps from a ten year old Crown (!) PA that actually rattled when removed... :D

Don’t forget, when it’s ones own equipment going a little too far isn’t really a bad thing, it’s part of the fun.
 
My rule for stuff like this is simple: If a device that is 15+ years old begins to blow fuses or otherwise malfunction (this is my telltale sign), then it gets recapped. No sniffing, no measuring, I don't bother looking for bulges. I just assume the manufacturer was cheap and replace the caps.

ALL of them - even those surface mount electrolytics, they fail too!

This has helped me to resurrect 90% of failed electronics over the past 20 years or so.
 
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The bottom line here is this......
It usually depends on the vendor/manufacturer at the time who made the capacitors for a particular product.

Some electrolytics last decades without a problem, show no signs of aging, others fail in less than 10 years.
So to do a full "recap" in some cases is not needed, although through the internet and its plethora of so-called helpful "advisers", this "recap craze" has made people paranoid puppets.
Most of it was started in the early-mid 2000's, when there was a real problem with some "bad caps" that had faulty chemical makup due to a stolen formula.
Once it was published online (the bad caps forum, among others) it took off like a rocket ship.



I compare this to the actual percentage of products (audio and video, etc) that have come to my shop over the decades with real, actual capacitor-related failures.
Don't let the "advisers" make you nuts over this, because a lot of it is just blabber talk.
 
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