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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Thu 07, 2017 10:42 am 
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Testing old caps is a waste of time.

Case in point; I received an eBay win yesterday, a micro sized radio. Powering it up produced hiss, and the second radio test displayed that the osc and power circuits were working.

The first Electrolytic I replaced enabled the set to start offering station reception, albeit with oscillation. Just for the hell of it, I used my capacitance meter on the original, and it showed a reading commensurate with it's printed value.

Now the larger question is, when I threw it toward the waste basket, it missed.

Does this prove...

1. Divine intervention...The capacitor is innocent of any wrong-doing. Or

2. I have a lousy aim.

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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Thu 07, 2017 1:17 pm 
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Location: Long Island
Quote:
You guys are poo pooing Yellow Caps. But have either of you actually done ANY testing large or small?
No... right?
lol


Yes I have. If you buy your caps from name brand suppliers, it's very unlikely you'll ever find anything out of spec or marginal. What they tell you you are getting, is what they say it is. But if you buy no-name caps of dubious ancestry you may find that they measure okay for C, but leakage or dissipation or tan-delta vary from one cap to the next. You find that leakage may be appreciable in some of these caps at their marked voltage ratings and there's no margin beyond that. No-name electrolytics may have barely enough electrolyte in them to function for more than a couple of years.

Quote:
Any such tests would be completely meaningless.

The "yellow caps" to which you refer are anonymous, with no maker or series identification.

So if you test five batches, they might all be identical, or all different.

What have you learned, and how would it apply to the next cap you picked up?


It would mean you should be picking up your caps from a different place.

Quote:
his thread is supposed to be about testing and checking OLD filter caps. Right?
... And I don't care if you like to do that. Go ahead.
It makes no sense for me to do it however because testing 50yo caps will never restore them to anything like new or even close to any newly manufactured cap made anywhere today.

So if testing old caps cannot restore them to new.. I ask then, ... why waste time doing it??
And again.... just like the spilled milk example. Why keep testing if it is spilled.. lol
.. No matter what you do ..you can't salvage it.
Any realist has enough logic to comprehend this.


I think it is ironic that you mentioned ISO-9000/9001, which are part of a family of standards for quality management and control. How do you think that control is achieved, except by sampling and testing the product being manufactured? Okay, so you're going to tell me that this is about old capacitors, not new ones. You think it's a pointless waste of time to test them because of the likelihood that they will test bad, and you are going to change them regardless. Of course twiddling the dials on a capacitor tester is a waste of time if you do not know or care how to interpret the results. But I say that there is a story behind every failure and there may be something instructive to be gained if you know where to look.

    What is the failure mode? Is it an old age dry-out failure, a hard short, or an open? If it's a dry-out, it is possible that the equipment or at least the capacitor was still working when it was put into storage. In that case, little else might be wrong with the equipment. But if you find a cap that died a painful death, the questions then become, did something cause the failure? Did the cap fail catastrophically and damage other parts?

    What were the secondary characteristics of the capacitor (the things beyond uF's and volts)? Even though it may be too leaky for further use, it is still possible to measure AC characteristics like capacitance and dissipation or power factor as long as the cap isn't shorted or completely open. I've mentioned Q and self-resonant frequency in other threads. One can also measure dielectric absorption with a few simple items and gain some further insight into what type of capacitor you need to make a proper replacement. If you are replacing a power supply cap in an old five tube table radio, we can pretty much conclude that they used filter caps with "slow" electrolytes giving lowest ESR at 60-Hz. But coupling caps in solid state power amplifiers might have had ultra low leakage current, "fast" characteristics for better performance at high frequencies. Even the filter capacitors in high quality audio gear were often ultra-low ESR types since low level noise and power supply impedance may be critical in audiophile equipment but not worth the bother in a table radio.

    Finally, if you do keep old caps in service where possible for the sake of originality, or because the old caps had unique characteristics which cannot be obtained in modern replacements (often the case in large can caps), the only way to do it safely is to test them thoroughly.

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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Thu 07, 2017 1:51 pm 
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Awful lot of chat about a subject that is so obvious.


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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Thu 07, 2017 3:56 pm 
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A bit off-topic: ISO9000/9001 is mostly a paperwork exercise; such certification hardly ensures that the firm actually follows their documented quality control process, or that their process is indeed sound.

Capacitors always seem to bring out the best in us. I'll just summarize by saying that in an antique consumer radio or service grade piece of test equipment, the 40-50 year old electrolytics, especially those in the power supply circuitry, should be changed as a matter of course, as there is no benefit to continue using them, but lots of drawbacks. What one does with the old capacitors (leaves them in, tests them, throws them out) is really up to the individual.


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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Thu 07, 2017 8:14 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Hubbard, Oregon, U.S.A.
"Testing old caps in that context absolutely IS a waste of time.
It's based on an assumption that some might still be good.
In the case of old electrolytics, that's a dream worthy of the best high-priced stuff. "

One chap was trying to sell OLD salvaged paper capacitors, calling them film capacitors, and electrolytic capacitors on E(vil) Bay, so I tried to inform him. I did convince him that the paper capacitors were not poly film, as he thought they were, but I could
not convince him that the old electrolytics were not worth selling, because years ago, he "reformed" some that lasted several years, he said.


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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Thu 07, 2017 10:15 pm 
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Chris108 wrote:
Finally, if you do keep old caps in service...
the only way to do it safely is to test them thoroughly.[/list]

But no test is predictive.

Even when the parts were new, testing one would not tell you whether another would fail.

With old caps, that truth is multiplied by many powers of 10.
In particular, the tests do not tell you when (not if) the cap will fail.

- Leigh

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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Thu 07, 2017 10:28 pm 
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Chris108 wrote:

Finally, if you do keep old caps in service where possible for the sake of originality, or because the old caps had unique characteristics which cannot be obtained in modern replacements (often the case in large can caps), the only way to do it safely is to test them thoroughly.[/list]

OMG Chris... I can't belive all this!
... Seriously, the only realistic place that any sane technical-person, worth his salt, would "keep" an old e-cap ( esp one made in the previous century) is in the trash can or on a glass shelf in a museum.
....but certainly NOT "in service" in an active circuit anywhere !! ... yikes!

... now... please let me shoot myself.... lol

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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Fri 08, 2017 12:13 am 
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Just found this, any of you need it?


Attachments:
string.jpg
string.jpg [ 98.03 KiB | Viewed 124 times ]

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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Fri 08, 2017 12:23 am 
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Location: Mpls, Minnesota
Pbpix wrote:
Chris108 wrote:

Finally, if you do keep old caps in service where possible for the sake of originality, or because the old caps had unique characteristics which cannot be obtained in modern replacements (often the case in large can caps), the only way to do it safely is to test them thoroughly.[/list]

OMG Chris... I can't belive all this!
... Seriously, the only realistic place that any sane technical-person, worth his salt, would "keep" an old e-cap ( esp one made in the previous century) is in the trash can or on a glass shelf in a museum.
....but certainly NOT "in service" in an active circuit anywhere !! ... yikes!

... now... please let me shoot myself.... lol

Most of my Tek test equipment is running on the original capacitors

Dave


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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Fri 08, 2017 12:54 am 
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This person can't spell either.
Paradox.
So what's actually in that box?

Image

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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Fri 08, 2017 1:08 am 
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easyrider8 wrote:
Most of my Tek test equipment is running on the original capacitors
Hi Dave,

The same is true for all of my decades-old HP and Tektronix gear.

But there's a HUGE difference in quality between the parts they used and consumer parts.

- Leigh

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Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: How to Tell if a Filter Cap is Really Bad ????
PostPosted: Dec Fri 08, 2017 2:20 am 
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Leigh wrote:
easyrider8 wrote:
Most of my Tek test equipment is running on the original capacitors
Hi Dave,

The same is true for all of my decades-old HP and Tektronix gear.

But there's a HUGE difference in quality between the parts they used and consumer parts.

- Leigh

I agree.
I still have a handful of 2uf - 60uf low voltage, mil-spec quality, e-caps from my days at Bendix in the 1960s.
These great caps were designed for gvt aero-space use. So I'm pretty sure they are still good.
When I measure the uf value they seem to be fine, and I'd be tempted to use them just for a fun test circuit.
I have no proper method to measure anything else except leakage with an ohm meter.

But nowadays I can find nicer, smaller sizes w/larger voltages and uf values so it doesn't make a lot of sense.

Last year I used a couple in a multi-vibrator LED blinking circuit. They worked perfectly and I just put a new 9v battery on the ckt and sure enough it's still blinking nicely.

But we're talking about mil-specs and aerospace quality here.
... so these were really built for the long duration.

Attachment:
mil-spec caps.jpg
mil-spec caps.jpg [ 67.73 KiB | Viewed 103 times ]

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