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<p>Have a hunt for the Peak Atlas testers - eg. ESR60<br>
Very good for such specific tasks (electro caps - presume tants
too) and not too expensive.<br>
</p>
<div class="moz-cite-prefix">On 06/02/2020 21:01, Pete Hartman
wrote:<br>
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cite="mid:CACodTR_w8fC8-zkbARWvV-5RU+MGuywC5FGxqzNbEZXNpynraw@mail.gmail.com">
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<div dir="ltr">Do such things actually work reliably in circuit?<br>
<br>
e.g. my cap meter or the cap meter setting on my multimeter
absolutely do not work with caps soldered into a circuit.<br>
<br>
pete</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Thu, Feb 6, 2020 at 2:51 PM
Jimmy Moore <<a href="mailto:jamoore84@gmail.com"
moz-do-not-send="true">jamoore84@gmail.com</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div>>Electrolytics can last a long time. I have a
British tube guitar</div>
amplifier from 1963, I expected to need new caps with an amp
that old.<br>
When my guitar tech inspected it he said the original caps
were fine.<br>
Why? The amp design allowed heat to rise in open air to
prevent<br>
accumulated heat, thus it prevented the premature decay of
the caps.<br>
That's over 50 years on the original caps!
<div><br>
</div>
<div>No shade intended toward your guitar tech, but how did
he test them? simple capacitance check can read in-spec,
but the ESR can make it very leaky. I've wanted to build
a capacitor checker as a side-project, it seems like it
would be a useful device:</div>
<div><br>
</div>
<div><a href="https://www.youtube.com/watch?v=LhovRIM5xAo"
target="_blank" moz-do-not-send="true">https://www.youtube.com/watch?v=LhovRIM5xAo</a> </div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Thu, Feb 6, 2020 at
1:32 PM Michael E Caloroso <<a
href="mailto:mec.forumreader@gmail.com" target="_blank"
moz-do-not-send="true">mec.forumreader@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">I do not subscribe to
the convention of blanket recapping of old gear.<br>
The prevailing "recap" convention is a carryover from
guitar amps.<br>
<br>
The significant contributor to cap degradation is heat.
Guitar amps<br>
and class A/B power amps generate a lot of heat and this
dries out the<br>
caps, so a recap is warranted. Not the case with most pro
audio and<br>
synth gear as they don't generate that much heat. There
are some<br>
exceptions some pro audio gear and synth do generate high
heat. If<br>
your rack gear are tightly packed this can create an
environment where<br>
high heat can exist.<br>
<br>
Heat aside, caps do fail due to age or faulty design and
should be<br>
replaced period. Tantalum caps from the 1970s/80s are
notorious for<br>
failing with age with a short circuit (not cool on power
rails). The<br>
cases on Mullard "tropical fish" caps crack with age.
Some brands<br>
have a bad reputation - RIFA caps are notorious for
exploding. About<br>
fifteen years ago there was a run of electrolytic caps
from Asia that<br>
were built from a stolen design, and there were massive
failures in<br>
the field. These caps were used in consumer products
including<br>
computers, and you can see the visible bulge in the tops
of the cases<br>
as they fail. We had a rash of failed computers at work.<br>
<br>
Other than that, if it ain't broke then don't fix it. I
took<br>
before/after pics of the power rails on the 'scope during
a recap of<br>
an OBX and found no improvement.<br>
<br>
Caps can drift from their original value and render a
tuned circuit to<br>
malfunction, a cap meter or impedance bridge are good
tools to test<br>
the caps. On the other hand, if I see polyester caps in a
tuned<br>
circuit I have substituted better dielectric caps and
gained better<br>
performance. Processors like phasers can sound better
with the proper<br>
dielectric.<br>
<br>
Teflon or glass are the most reliable dielectrics but you
will never<br>
see them in pro audio or synth gear because of their
cost. Caps will<br>
fail for one reason or another regardless of dielectric.<br>
<br>
Electrolytics can last a long time. I have a British tube
guitar<br>
amplifier from 1963, I expected to need new caps with an
amp that old.<br>
When my guitar tech inspected it he said the original caps
were fine.<br>
Why? The amp design allowed heat to rise in open air to
prevent<br>
accumulated heat, thus it prevented the premature decay of
the caps.<br>
That's over 50 years on the original caps!<br>
<br>
Bad design will ruin caps. There are products using caps
with 16V<br>
maximum voltage rating on 15V power rails! That's asking
for trouble<br>
with such a close margin. Failing to secure large caps
from movement<br>
will eventually crack the solder joint(s) and/or the
bond(s) to the<br>
leads.<br>
<br>
MC<br>
<br>
On 2/6/20, MTG <<a
href="mailto:grant@musictechnologiesgroup.com"
target="_blank" moz-do-not-send="true">grant@musictechnologiesgroup.com</a>>
wrote:<br>
> I'm starting to see a lot of failures on Yamaha units
with switching<br>
> power supplies. Basically all the hits from the 80's.
On the items I've<br>
> fixed, I replaced the electrolytics on the PS, but
not the various<br>
> "main" boards. YMMV.<br>
><br>
> GB<br>
><br>
> On 2/6/2020 10:14 AM, John Speth via Synth-diy wrote:<br>
>> Hi folks-<br>
>><br>
>> Today I called a shop about replacing the belts
on my 30 year old<br>
>> cassette tape deck (Fostex X-26). The guy quickly
recommended also<br>
>> replacing the caps (I assume just the
electrolytics). I'm guarded<br>
>> against folks who do repairs on stuff that don't
show signs of need,<br>
>> which my tape deck doesn't.<br>
>><br>
>> What are the prevailing opinions on replacing old
electrolytics in<br>
>> equipment from the 1980's?<br>
>><br>
>> I hope I didn't start an opinion war.<br>
>><br>
>> Thanks - JJS<br>
>><br>
>><br>
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