[sdiy] How do old electrolytics go bad?

[Scott Nordlund]

It's worth saying also that sometimes the tolerance is something like -20/+50%

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> Date: Fri, 6 Feb 2009 15:40:34 -0700
> From: sounddoctorin at imt.net
> To: igg.debus at t-online.de
> Subject: Re: [sdiy] How do old electrolytics go bad?
> CC: Synth-diy at dropmix.xs4all.nl
>
> I typically see old electro's drift higher and higher..even to 10X the
> original value and then they'll plummet often to dead or they'll even
> short sometimes. This in observing Fender and other amps of various
> ages largely.
>
> The *source* of this phenomena, I assume, is that the electrolyte
> gradually degrades and in doing so some functional distances may be
> altered..and of course closer plates mean higher capacitance. Shrinkage
> of the dielectric material. And then as it gets too close it punctures
> and leaks sometimes. Or something totally disconnects in other cases.
> Not sure but rambling possibilities anyway :-)
>
> Anyway that phenomena is common whatever the case, let me assure you. -Bob
>
> Ingo Debus wrote:
>
>> Hi,
>>
>> we all know that electrolytic capacitors often go bad when they are
>> old. In the past I had replaced some that had a significantly lower
>> than rated capacitance. But now I got two that show a higher than
>> rated value on my DMM: one is rated 100uF/3V and shows 270uF on the
>> meter, the other is rated 16uF/16V and shows 23uF. Of course I
>> desoldered them from the circuit before measuring.
>> Is this normal? Or did they have the higher values from the
>> beginning? Or are they leaking and thus fooling my meter?
>>
>> I estimate these caps are about 40 years old.
>>
>> Ingo
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>>
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