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Old 2nd March 2012, 11:30 PM   #1
JdAo is offline JdAo  Portugal
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Default Vintage: Everyone is just replacing capacitors, what about other components ?

I think this might make the super high prices on some 70's or even earlier equipment look really stupid, but why are most folks just replacing capacitors ? I find capacitors are almost the only thing mentioned when reconditioning vintage equipment. What about other components ? Is there any study on the average degradation of resistors for example ? Aren't we just overlooking the whole thing and should be replacing a lot of other stuff ?

[EDIT]
I say we, well I'm just a beginner without electronics education but I think this thread could be a very useful reference and experience sharing thing...
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Old 3rd March 2012, 12:12 AM   #2
Enzo is offline Enzo  United States
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Among other things, I service jukebox amps, and some are even older than world war 2. SO resistors do shift in value, especially older ones.

One difference between resistors and caps, in my view, is that dried out/leaky caps can cease to function or even cause damage. In the signal path, leaky old waxed paper caps can send DC voltage to places it doesn;t belong, dried up filters can leave the power supply hummy, shorted caps can damage other parts. Resistors can open, but mainly they tend to rise on value. They don;t short, and there is no dielectric to get leaky. SO in general, if a 220k resistor goes up to 290k, the amp will probably still work. It won;t hurt it. Will it be optimal? Probably not, but that is another story.


Caps on old equipment usually need changing out en masse. So it gets discussed. That doesn't mean we ignore all the other things, but they are probably less urgent.
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Old 3rd March 2012, 12:28 AM   #3
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Well, all electrolytic capacitors are well known parts that "dry out" with time and when they do, they can damage many other parts. I used to work fixing TVs, and Sony was well known with pip boards problems that affected the picture and the problem was with dry surface mount capacitors. as soon as you replaced those tiny caps on the pip boards..you got picture back!!! electrolytic capacitors are very critical and when they dry out...you will know for sure!. The best intrument to test an electrolytic cap is an ESR meter. (something like this) This one is way better than those digital ones. I got this one from a gentleman that worked fixing equipments for hospitals and build these ESR meters.

PS: Even the new LCD and plasma TVs today are well known for this problems with dry out caps in the power supply that affect Sound, video and power on!!!
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Old 3rd March 2012, 02:42 AM   #4
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Agreed.
Very simply, the capacitors in question are electrolytic right? They are wet cells, akin to ordinary batteries, which means they won't last forever. In fact, most manufacturers now rate these at only 2 or 3,000 hrs or so MTBF at rated load. By contrast, other components are "solid state" and so have no significant physical or chemical changes occurring in use or storage. Some could last a lifetime.

Some DIYs take great pride in swapping all the jelly bean parts for more cute up-market ones but this is usually just a matter of personal taste. However, dried-out electrolytics are a matter of necessity - preferably replaced before they fail and perhaps take out other more difficult to replace parts with them.

So yes, recapping justifies full attention in old (20 years +) amplifiers or even any newer, hot running electronics for that matter. Anyone servicing SMPS consumer equipment will be well aware of this electrolytic cap. MTBF issue.
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Old 3rd March 2012, 05:17 AM   #5
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As said above, caps are the thing most apt to fail, though a lot depends on the particular cap and the environment it lives in. IMO an awful lot of caps get replaced for no intelligent reason. Carbon composition resistors tend to rise in value as they age, but finding exact replacements can be difficult or expensive. Some people think they sound better. You can install a superior modern resistor but some will say it sounds worse. Carbon film and metal film resistors are stable for all practical purposes and should last the life of the equipment. The same for most transistors and ICs, except for old germanium devices that didn't hold up too well.
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Old 3rd March 2012, 07:00 AM   #6
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Conrad is right but there is more to it ....often beyond caps and resistors trimmers need to be replaced even better with multiturn and also quite as often small signal transistors might have various issues

one funny case i remember was a pioneer amplifier that i was working with that had a transistor with a "mechanical" error IE: something was loose or broken inside one of the output transistors and while the amp measured, idle and play very fine Tick the transistor with a screwdriver and relay clicks ... or power up to a certain level and also relay clicked ...

other funny case was a reel to reel AKAI that had a lot of hiss while at play back and no electrolytics or very good cleaning that was done helped in any way .....traced the fault in one transistor in the head preamp with freezer spray and while freezing it the hiss was gone .... replaced all 4 transistors with better type lower cob/ higher Ft / higher beta and lower noise and become dead quiet /.....

kind regards
sakis
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Old 3rd March 2012, 07:37 AM   #7
sbrads is offline sbrads  United Kingdom
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Speaking as someone who has to get up to 20 yr old military electronics back to fully meeting as new specification I think I know what tends to suffer with age. The most likely weak components assuming a good design in the first place are.........

Polarised caps of any type going leaky or very low in capacitance value.

Solder joints. Usually joints crumbling and fracturing due to thermal cycling expansion/contraction effects or just by physical movement e.g. pcb mounted sockets.

Contamination causing leakage. Often due to vapours from leaking capacitors affecting things like wire insulation, plastics, rubber etc.

Dirty or corroded internal connectors.

PCB tracks fracturing, internal on multi-layer mainly.

Then it's stressed components pushed near to their limits, some are bound to fail eventually.

I've probably forgotten some, there's so many failure modes but most can be attributed to design constraints apart from leaky caps.
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Old 3rd March 2012, 04:01 PM   #8
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Here is an ESR tester that is currently available. It is said to be quite good, but I don't have one myself, so I can't vouch for it (I would like one, but finances do not permit it at present).

Click the image to open in full size.


More info at
Peak Electronic Design Limited - Atlas ESR - Equivalent Series Resistance Meter and Capacitor Analyser - Model ESR60
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Old 3rd March 2012, 10:13 PM   #9
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Here is information on the Creative Electronics ESR meter in post #3:
http://bama.edebris.com/manuals/creative/esr
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Old 4th March 2012, 04:14 PM   #10
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If dc offset cannot be adjusted, I have found in my journeys in vintage equipment that the transistors that deal with this (differential pair) often need to be replaced, due to the originals not being well matched. An amplifier with high dc offset (over 50mV) usually sounds very harsh and downright unpleasant. Useless.
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