<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 7 Feb 2020, at 7:01 am, Pete Hartman <<a href="mailto:pete.hartman@gmail.com" class="">pete.hartman@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Do such things actually work reliably in circuit?<br class=""><br class="">e.g. my cap meter or the cap meter setting on my multimeter absolutely do not work with caps soldered into a circuit.<br class=""><br class="">pete</div></div></blockquote><div><br class=""></div><div><br class=""></div><div>Pete, I bought one of these a few years ago</div><div><br class=""></div><div><a href="https://evbesrmeter.pt/index.htm" class="">https://evbesrmeter.pt/index.htm</a></div><div><br class=""></div><div>which is designed to be used in circuit (powered down). It is essentially a “low ohms” meter, using a pulsed signal I believe.</div><div>I can say that is has reliably identified faulty electrolytics in a variety of vintage gear dating back to the 60s, so no more guessing and shot-gunning the repairs.</div><div><br class=""></div><div>Adam</div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><br class=""><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" class="">jamoore84@gmail.com</a>> wrote:<br class=""></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" class=""><div class="">>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 class="">When my guitar tech inspected it he said the original caps were fine.<br class="">Why? The amp design allowed heat to rise in open air to prevent<br class="">accumulated heat, thus it prevented the premature decay of the caps.<br class="">That's over 50 years on the original caps!<div class=""><br class=""></div><div class="">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 class=""><br class=""></div><div class=""><a href="https://www.youtube.com/watch?v=LhovRIM5xAo" target="_blank" class="">https://www.youtube.com/watch?v=LhovRIM5xAo</a> </div><div class=""><br class=""></div><div class=""><br class=""></div></div><br class=""><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" class="">mec.forumreader@gmail.com</a>> wrote:<br class=""></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 class="">
The prevailing "recap" convention is a carryover from guitar amps.<br class="">
<br class="">
The significant contributor to cap degradation is heat. Guitar amps<br class="">
and class A/B power amps generate a lot of heat and this dries out the<br class="">
caps, so a recap is warranted. Not the case with most pro audio and<br class="">
synth gear as they don't generate that much heat. There are some<br class="">
exceptions some pro audio gear and synth do generate high heat. If<br class="">
your rack gear are tightly packed this can create an environment where<br class="">
high heat can exist.<br class="">
<br class="">
Heat aside, caps do fail due to age or faulty design and should be<br class="">
replaced period. Tantalum caps from the 1970s/80s are notorious for<br class="">
failing with age with a short circuit (not cool on power rails). The<br class="">
cases on Mullard "tropical fish" caps crack with age. Some brands<br class="">
have a bad reputation - RIFA caps are notorious for exploding. About<br class="">
fifteen years ago there was a run of electrolytic caps from Asia that<br class="">
were built from a stolen design, and there were massive failures in<br class="">
the field. These caps were used in consumer products including<br class="">
computers, and you can see the visible bulge in the tops of the cases<br class="">
as they fail. We had a rash of failed computers at work.<br class="">
<br class="">
Other than that, if it ain't broke then don't fix it. I took<br class="">
before/after pics of the power rails on the 'scope during a recap of<br class="">
an OBX and found no improvement.<br class="">
<br class="">
Caps can drift from their original value and render a tuned circuit to<br class="">
malfunction, a cap meter or impedance bridge are good tools to test<br class="">
the caps. On the other hand, if I see polyester caps in a tuned<br class="">
circuit I have substituted better dielectric caps and gained better<br class="">
performance. Processors like phasers can sound better with the proper<br class="">
dielectric.<br class="">
<br class="">
Teflon or glass are the most reliable dielectrics but you will never<br class="">
see them in pro audio or synth gear because of their cost. Caps will<br class="">
fail for one reason or another regardless of dielectric.<br class="">
<br class="">
Electrolytics can last a long time. I have a British tube guitar<br class="">
amplifier from 1963, I expected to need new caps with an amp that old.<br class="">
When my guitar tech inspected it he said the original caps were fine.<br class="">
Why? The amp design allowed heat to rise in open air to prevent<br class="">
accumulated heat, thus it prevented the premature decay of the caps.<br class="">
That's over 50 years on the original caps!<br class="">
<br class="">
Bad design will ruin caps. There are products using caps with 16V<br class="">
maximum voltage rating on 15V power rails! That's asking for trouble<br class="">
with such a close margin. Failing to secure large caps from movement<br class="">
will eventually crack the solder joint(s) and/or the bond(s) to the<br class="">
leads.<br class="">
<br class="">
MC<br class="">
<br class="">
On 2/6/20, MTG <<a href="mailto:grant@musictechnologiesgroup.com" target="_blank" class="">grant@musictechnologiesgroup.com</a>> wrote:<br class="">
> I'm starting to see a lot of failures on Yamaha units with switching<br class="">
> power supplies. Basically all the hits from the 80's. On the items I've<br class="">
> fixed, I replaced the electrolytics on the PS, but not the various<br class="">
> "main" boards. YMMV.<br class="">
><br class="">
> GB<br class="">
><br class="">
> On 2/6/2020 10:14 AM, John Speth via Synth-diy wrote:<br class="">
>> Hi folks-<br class="">
>><br class="">
>> Today I called a shop about replacing the belts on my 30 year old<br class="">
>> cassette tape deck (Fostex X-26). The guy quickly recommended also<br class="">
>> replacing the caps (I assume just the electrolytics). I'm guarded<br class="">
>> against folks who do repairs on stuff that don't show signs of need,<br class="">
>> which my tape deck doesn't.<br class="">
>><br class="">
>> What are the prevailing opinions on replacing old electrolytics in<br class="">
>> equipment from the 1980's?<br class="">
>><br class="">
>> I hope I didn't start an opinion war.<br class="">
>><br class="">
>> Thanks - JJS<br class="">
>><br class="">
>><br class="">
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