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Ageing Capacitors

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m1keC

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I recently started work on recapping an Akai AS980 quadraphonic receiver and thought you might like to know that having replace the 2200uF electrolytics on the output they all4 tested as 1100-1200uF. So, although they all tested as still being capacitors, they had lost about half of their rated value. I'll include a circuit diagram - the cap is C8 2200uF.
Screenshot 2020-01-25 at 07.58.34.png
 

proufo

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While you all are at it, could someone share his experience in using legged capacitors (say, Wondercaps) in circuit boards that have SMD ones?

It looks it would be easy, but there is no info anywhere (nor YouTube videos).

Thanks in advance.
 

gene_stl

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SMD caps probably ought to be replaced with SMD caps. You could drill the contact land and put the wire through but you would be entering a new land. The wires would add inductances.
 

jimfisheye

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Modern PC boards are often multi-layer with ground planes and internal connections. Careful with that drill, Eugene! (Yes, I do listen to too much Pink Floyd.)

If you're thinking of replacing with a better quality and/or higher voltage cap because the original part was under spec'd (this is a thing), you should be able to pull that off. There could be edge cases where you let in some noise or let out some RF if it turns out that area on the board had some tight tricky placement stuff going on to battle that.
 

DuncanS

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In general I would say replace like with like, so capacitance, dielectric material and rated voltage - or with a higher rated voltage.

If SMD capacitors were used with wires, then the wires would only add inductance of the order of 10nH or less, so would be insignificant at audio frequencies as the inductive impedance is 2 x Pi x Frequency x Inductance.
 

quadsearcher

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SMD electrolytics can be replaced with leaded electrolytics, just need to trim and shape the leads to the size of the pads. Did it in the 90s restoring camcorders. Big boutique capacitors would not physically fit and the weight could tear circuit traces, although for small values, newer poly caps are getting a lot smaller.
 

proufo

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SMD electrolytics can be replaced with leaded electrolytics, just need to trim and shape the leads to the size of the pads. Did it in the 90s restoring camcorders. Big boutique capacitors would not physically fit and the weight could tear circuit traces, although for small values, newer poly caps are getting a lot smaller.
Many many thanks!

Also many thanks for the other replies.
 

Sonik Wiz

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I recently started work on recapping an Akai AS980 quadraphonic receiver and thought you might like to know that having replace the 2200uF electrolytics on the output they all4 tested as 1100-1200uF. So, although they all tested as still being capacitors, they had lost about half of their rated value. I'll include a circuit diagram - the cap is C8 2200uF.View attachment 45583
In another post by Kirk referring to July '72 AUDIO magazine I found this that I think is relevant:

Capacitor Life Span
Q. Do mylar tubular capacitors and
ceramics deteriorate with age? If so, is
the deterioration gradual or is there
usually a sudden failure? If gradual,
what is the effect upon power amplifier
performance? Is there an average life
span for these components, beyond
which replacement is advisable?
Similar advice re electrolytic capac-
itors will be appreciated.-Walter Diehl,
Great Neck, N.Y.

A. Tubular paper capacitors and
ceramic units do not usually fail; their
life span is indefinite. When they do
fail, however, they will fail suddenly
and completely. They will either com-
pletely short or they will open.
Electrolytics will fail after a time. I
do not know if we can specify a defi-
nite life span for them, but perhaps
ten years is about what can be ex-
pected of most of them. Some will last
longer and others a shorter length of
time. Electrolytic capacitors fail grad-
ually, losing their capacitance little by
little,
Depending upon their location
in a circuit this gradual decrease in
capacitance can lead to loss of bass
response, crosstalk between channels,
leakage of signal even with the gain
control turned down fully, motor -
boating, and hum.

As is true of paper and ceramic
capacitors, electrolytics are also sub-
ject to catastrophic failure. Sometimes,
too, the internal connections between
the lugs and the foil can become de-
fective, leading to intermittent opera-
tion of the capacitor.

If you have electrolytic capacitors
in the "junk box," you may find that
they deteriorated in another respect.
Their breakdown voltage may become
lower than their nominal rating. If
you plan to use a capacitor which has
been stored for long periods, you can
take precautions to see that it does not
fail when placed in service. You can
reform the electrolytic coating. This
requires the use of a variable voltage
power supply. Connect the capacitor
in series with a resistor whose value
is in the order of 50K or 100K ohms,
ten watts. Connect this series com-
bination across the power supply,
being careful of polarity. If the capac-
itor is rated at 450 V, start with ap-
proximately 200 volts. Over a period
of several hours, gradually bring up
the voltage to the rated value. You
should allow at least 12 hours for this
operation.

It is possible that the capacitor
will short out during this reforming
process. Of course, it must then be
discarded. The resistor, therefore, is
used to limit the current flowing in
the circuit, thereby protecting the
power supply from possible damage.
Edit:
Well now I'm thinking I should check the value of the power supply caps in my oldish Adcom 555 power amps. Tho I must admit they fire up fine & no audible discrepancies. Still I am an occasional victim of audio nervosa.
 
Last edited:

Telegraph Audio

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Dec 15, 2019
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I recently started work on recapping an Akai AS980 quadraphonic receiver and thought you might like to know that having replace the 2200uF electrolytics on the output they all4 tested as 1100-1200uF. So, although they all tested as still being capacitors, they had lost about half of their rated value. I'll include a circuit diagram - the cap is C8 2200uF.View attachment 45583
They lose their value over time, capacitors must be changed. The technique requires attention and some elements need to be changed over time. This is what we say as professionals. We use high quality parts, but they also have their own time.
 

ar surround

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They lose their value over time, capacitors must be changed. The technique requires attention and some elements need to be changed over time. This is what we say as professionals. We use high quality parts, but they also have their own time.
And don’t forget about replacing the NPE capacitors in older speakers. They have a lifetime as well. Failure of a series capacitor in the electrical chain of a tweeter or midrange can result in a catastrophic damage to the driver...Although dulling of the sound over time is more likely.
 

MidiMagic

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Messages
332
Electrolytic capacitors tend to lose capacity and max voltage when they are idle. This usually does not happen while they are in daily use.
 

Telegraph Audio

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Dec 15, 2019
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Location
Kuiv,Ukraine
Electrolytic capacitors tend to lose capacity and max voltage when they are idle. This usually does not happen while they are in daily use.
If the storage conditions (temperature and humidity) are violated, the loss occurs even faster. If the equipment operates in unacceptable conditions, then capacitors will lose capacitance and maximize voltage.
 
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