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Symptoms and Repair of Bad Caps.

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62sunbeam

62sunbeam

Raconteur
I have a few units I'm trying to get back up to snuff and while a few have what I believe to be bad pots or sliders which I plan to clean with deoxit I was wondering what are the tell tail symptoms of bad capacitors and what does it take to replace them?

Do I just find caps with matching specs at the local Fry's or do I want something special and where would I get these "special" caps?

In a given unit how do I determine which are the likely bad units?

Thanks in advance.

Eric
 
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Shrunken sleeves, bulging, liquid around the bottom, corrosion on nearby parts.
http://amp8.com/etc/amp-inho/c-test.htm
The caps most likely to need replacing are in the power supply.
Most of the caps you need can be found at Mouser and Digi-Key.

What many people do is replace every electrolytic cap in the unit, as 20+ year old caps are past their prime.
 
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Get Advice

My opinion is that you should get professional advice. A lot of people are "experts" parroting the received wisdom. Here's a quote from an email I got concerning this very subject:

Most of the time, we find that the vintage gear benefits most from a
good cleaning of the switches, controls, and speaker relays,
resoldering, and a good tuner alignment.

Be careful about those who say that recapping is necessary. We have
seen many units which have been almost ruined by someone who thought
they knew better than the original designer of the set.


So I'd put off pulling the trigger on caps until you've done these things first.
 
Well, most of the people here who recommend replacing caps in vintage equipment have done it themselves and have heard the results with thier own ears.

We have no idea where that statement you highlighted came from.
 
Many are ruined by NOT recapping.... but explore the subject here, do a search and you will at least be able to identify visual signs of a bad or failing cap. Thanks to the techs here many a novice has been able to avoid the "puff-a-smoke" experience.
 
Is there a sound or other symptom of bad or going bad caps?
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Depends on the circuit where the cap is used. Sometimes the only symptom will be a dead channel or dead unit as the failing cap takes out other components. This can make recapping vital for some units in order to prevent damage to NLA components.
 
LouStools said:
Most of the time, we find that the vintage gear benefits most from a
good cleaning of the switches, controls, and speaker relays,
resoldering, and a good tuner alignment.

Be careful about those who say that recapping is necessary. We have
seen many units which have been almost ruined by someone who thought
they knew better than the original designer of the set.


So I'd put off pulling the trigger on caps until you've done these things first.
Click to expand...

Yes, a good cleaning is the first step, but think of it this way, the original designed of the set probably figured it would hit the dumpster after ~10 years. And even if they didn't think of it that way, caps (especially electrolytic caps) do have a finite life. Even mediocre modern caps are much better than the originals with respect to tolerance and life.

The only way to be sure is to pull every single cap and do leakage and ESR tests, and even those won't catch 100% of bad caps. If you plan on keeping the unit for many years to come, there's no good reason not to recap.
 
One symptom is higher than proper ESR (Equivalent Series Resistance) -- can measure with ESR meter or with signal generator (square) and oscilloscope. Caps tend to increase ESR long before they go really, really bad, or bulge, etc as I understand it.
 
I for one have recapped probably three vintage units and countless speakers and have yet to find a single cap that did not test perfectly with a capacitance meter and esr meter. If you really believe recapping is a necessity, why not also replace all transistors? I've come across many bad ones, again, never a bad cap.
 
http://amp8.com/index.htm
This guy runs a repair service out of his home in Japan. He is a semi retired electronics technician. When he does an overhaul repair, every questionable part is replaced, caps included.
I myself have done two amp repairs. One was a Technics SU-8080 that worked, but had a bad hum. This unit had a failed filter cap in a secondary regulated circuit. I decided to do a complete recap. I have an ESR cap meter, and there was about 30% of the caps out of spec with either high ESR, and/or high or low by more than 20% capacitance. Since the amp was defective, I couldn't listen to it before the repairs. I will say that it sounds very very good now.
My second repair was a Luxman L-80V with a dead channel. Fixed the channel. Again, I recapped the entire unit, replacing all elctros. Not many measured bad, maybe 5% were marginal. This amp also sounds really good.
I have a Luxman L-430 that works great, but somehow the sound doesn't quite do it for me. Maybe a recap is in order?
 
As recently as the mid 90s, a +/- 20% tolerance spec on an electrolytic was common, was even wider prior to that. Caps showing signs of damage or leakage are obviously in need of replacement. Humming caused by bad filter caps, certainly. Amps that run hot more so than amps that don't, as heat dries out electrolytics. If you are having any kind of problem, chances are much higher that it is related to transistors, dirty pots, or elsewhere, not "bad caps." Mostly, 20 year old caps are fine and don't "need" replacement unless there are symptoms, but this being a hobby and re-capping relatively cheap, no valid reason is necessary to re-cap if one derives enjoyment from it and have the required equipment and skills.
 
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Blanket Statements Not Wise

RossW said:
Yes, a good cleaning is the first step, but think of it this way, the original designed of the set probably figured it would hit the dumpster after ~10 years. And even if they didn't think of it that way, caps (especially electrolytic caps) do have a finite life. Even mediocre modern caps are much better than the originals with respect to tolerance and life.

The only way to be sure is to pull every single cap and do leakage and ESR tests, and even those won't catch 100% of bad caps. If you plan on keeping the unit for many years to come, there's no good reason not to recap.
Click to expand...

I'm sorry, but blanket statements like this just don't make sense to me.

I got my advice from a reputable repair shop. This guy told me to slow my roll with respect to re-capping until the unit had been thoroughly cleaned and inspected, which seems more reasonable than to whipping out the soldering iron and getting busy, at least to me.

Why do I think this is good advice? Well, one reason is this guy could have made a ton of money by clamming up and doing what I suggested. Another is that you can always recap after you do a preventive maintenance on your equipment, but you can't undo the other. Really frogging things up if you just charge ahead is a distinct possibility.

I've been around too long not to recognize the seeds of disaster. It doesn't stop me from doing the wrong thing, mind you, but it does eliminate one avenue of excuse.

Again, this is just an opinion.
 
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LouStools said:
I'm sorry, but blanket statements like this just don't make sense to me.

I got my advice from a reputable repair shop. This guy told me to slow my roll with respect to re-capping until the unit had been thoroughly cleaned and inspected, which seems more reasonable than to whip out the soldering iron and getting busy, at least to me.

Why do I think this is good advice? Well, one reason is this guy could have made a ton of money by clamming up and doing what I suggested. Another is that you can always recap after you do a preventive maintenance on your equipment, but you can't undo the other. Really frogging things up if you just charge ahead is a distinct possibility.

I've been around too long not to recognize the seeds of disaster. It doesn't stop me from doing the wrong thing, mind you, but it does eliminate one avenue of excuse.

Again, this is just an opinion.
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Any caps that are 30+ years old have outlived their mean time between failures (MTBF). They may work, they may not. If I'm doing a repair for somebody, I'll do a quick ESR test in-circuit and replace any electros that are marginal. But if I'm going to listen to it in my livingroom, I'm going to replace all the caps. First, they're cheap, and second, as they age they do have an effect on the sound, no doubt about it. If replacing caps is a technical challenge for you, you may elect not to, but there are definite benefits to be had from recapping a 30-year-old unit.
 
There's a lot of loose talk about recapping, a lot of people getting into trouble in the effort, and practically zero hard evidence that it's necessary or beneficial. I'm talking about cases where the equipment is fully functional prior to cap therapy, and there's no obvious sign of capacitor deterioration, of course. It's not good enough to find a few caps postmortem that don't meet ESR specs, because this claim isn't backed up by quoting the original cap's ESR spec. ESR often isn't specified to begin with, for capacitors that aren't intended for power supply filtering applications. I would like to see a few before & after THD+N, frequency response, and noise measurements to back up all of the wild claims.

I do freely accept, by the way, that a recapped amp sounds different. I've demonstrated this effect very clearly to myself. What I don't accept is the claim that it's obviously better. Rigging for flame...
 
lukiedog said:
Mostly, 20 year old caps are fine and don't "need" replacement unless there are symptoms, but this being a hobby and re-capping relatively cheap, no valid reason is necessary to re-cap if one derives enjoyment from it and have the required equipment and skills.
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What he said.
 
I found out recently that a life of a cap at a nuke station is less than five years.

If it is for my equipment, why would I not follow the same guideline for the whopping total of $30 that it will cost me....

Plus, it is fun to get in there and change them out....
 
BinaryMike said:
I do freely accept, by the way, that a recapped amp sounds different. I've demonstrated this effect very clearly to myself. What I don't accept is the claim that it's obviously better. Rigging for flame...
Click to expand...

Can't argue with you there. I'll qualify my earlier post and say that in almost all cases (one particular H/K amp still stands out in my mind) the difference is a positive one in terms of sound quality.
 
http://amp8.com/etc/amp-inho/c-koukan.htm

BinaryMike said:
There's a lot of loose talk about recapping, a lot of people getting into trouble in the effort, and practically zero hard evidence that it's necessary or beneficial. I'm talking about cases where the equipment is fully functional prior to cap therapy, and there's no obvious sign of capacitor deterioration, of course. It's not good enough to find a few caps postmortem that don't meet ESR specs, because this claim isn't backed up by quoting the original cap's ESR spec. ESR often isn't specified to begin with, for capacitors that aren't intended for power supply filtering applications. I would like to see a few before & after THD+N, frequency response, and noise measurements to back up all of the wild claims.

I do freely accept, by the way, that a recapped amp sounds different. I've demonstrated this effect very clearly to myself. What I don't accept is the claim that it's obviously better. Rigging for flame...
Click to expand...

Myself, I recap as preventive maintenance.
 
I guaran-****ing-TEE you that we are NOT getting into a pissing match about whether recapping is necessary or not.

If you want to read the pro's and con's, and hear arguments galore on both sides, there a nice sticky in the Sansui forum. I believe every word that ever in life needs to be said on the subject has already been said there. Go read it.

Mods, please lock this thread.
 
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