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PICList Thread
'[OT] Short life on electrolytic caps'
2000\03\08@073404 by Roland Andrag

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face
Hello Everyone,

I have just (with somewhat of a shock) found out that electrolytic caps are
rated for only 2000 to 7000 hours of operation.  These ratings seem to be at
high temperatures, but nonetheless they make me feel very uncomfortable
about using them.  Is this some unspoken rule that somehow passed me by?

I would like to hear some comments on what caps are usually used in
differenent situations..

Thanks
Roland

2000\03\08@080145 by Spehro Pefhany

picon face
At 02:28 PM 3/8/00 +0200, you wrote:
>Hello Everyone,
>
>I have just (with somewhat of a shock) found out that electrolytic caps are
>rated for only 2000 to 7000 hours of operation.  These ratings seem to be at
>high temperatures, but nonetheless they make me feel very uncomfortable
>about using them.  Is this some unspoken rule that somehow passed me by?

That's usually 4% failures at that life. Usually consider life to double
for every 10'C lower.

>I would like to hear some comments on what caps are usually used in
>differenent situations..

That could fill a book, or at least a chapter..


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Spehro Pefhany                                    "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com
Fax:(905) 271-9838                      (small micro system devt hw/sw + mfg)
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2000\03\08@094123 by Alan Pearce

face picon face
>I have just (with somewhat of a shock) found out that electrolytic caps are
>rated for only 2000 to 7000 hours of operation.  These ratings seem to be at

Don't forget that ordinary electrolytic capacitors are filled with a liquid
which does eventually dry out. It is because they have a liquid in them that
they are called electrolytic.

If this sort of life is unacceptable at the temperature you require you will
need to use solid tantalum types.

2000\03\08@104836 by Wagner Lipnharski

picon face
Of course, an electrolytic capacitor stored at the drawer can survive
longer than 7000 hours.

When in operation is that it suffers all possible torture. A big torture
is temperature, so, strategies are in order to locate the capacitor away
from heat sinks, transformers, and so on.  

If your power supply has a blower, make sure the caps are in direct hit
with the air flow *BEFORE* the air gets warm from heat sinks and other
hot components.

Imagine two 10,000 µF capacitors rated for 16V, one is working with 15V,
another with only 3V, which one do you think is receiving more torture
and could get early problems?  The one with 15V for sure.  

Using electronic components at marginal values is only good for fuses,
and this is an interesting point. It is common to find power supplies
that consume 1 Amp at the output with a protection fuse of 1.5 or even
2A, since nobody wants that fuse to blow without any reason, isn't it?
But then, in the same power supply you can find a 10V capacitor
filtering 9Vdc... or even a LM317 regulator supplying 1.4A, it means,
everything is wrong, right?  To work at 9Vdc, the capacitor should stand
minimum 16V and the regulator should stand at least twice the output
current.

Chances are that installing a 50Vdc capacitor to filter 9Vdc output will
make this capacitor lasting longer than the regulator, the power
transformer, the wires, the metal case, and so on.

According to your numbers, 7000 hours is barely 10 months of continuous
operation.  I have some electronic devices around that are powered
continuously for more than 10 years... it is more than 86 thousand
hours...

Wagner


Roland Andrag wrote:
{Quote hidden}

2000\03\08@115112 by Alan Pearce

face picon face
>Imagine two 10,000 5F capacitors rated for 16V, one is working with 15V,
>another with only 3V, which one do you think is receiving more torture
>and could get early problems?  The one with 15V for sure.

Not necessarily. It is the heat generated by the ripple current through the
effective series resistance which is the main killer. This heat causes the
electrolyte to "boil off" and evaporate.

there is a disadvantage to the situation in the quote above. If a capacitor is
used at too low a voltage below its rated voltage, the electrolyte fails to
maintain the oxide film on the surface of the metal plates, and the effective
leakage resistance drops alarmingly, making the device look more like a resistor
than a capacitor.

How low is  too low below rated voltage? This can be a wet finger in the air
thing to guestimate, but it often is not a big problem, despite all I have just
said. Using the wrong capacitor as a filter capacitor in a power supply is most
likely going to be the cause of failure of a capacitor in a system, unless it
fails on the early slope of the bathtub curve.

2000\03\08@121437 by Wagner Lipnharski

picon face
I should agree with you, but unless practical experiences show me
different results, I always would choose a 10000uF @ 50V capacitor
instead a 10000uF @ 5V for a 5V application, at least I would have a
considerable lower ESR, lower resistance, lower generated heat. I
already saw few large caps exploding (protective caps and all), it is
never a nice picture.  I never thought about the reducing oxide film
effect with lower voltages, it also means that the oxide is reduced (or
even doesn't exist) when the equipment is powered off for quite some
time?  I really don't know much about it.
Wagner

Alan Pearce wrote:
{Quote hidden}

2000\03\08@124554 by Grif\ w. keith griffith

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<x-flowed>Back in the B+ days of tubes and such,,, if a cap was really old,,, you
would put a big value resistor in series with it and 'Reform' it,,, maby
over night,,, or over a weekend before putting it back in service after a
long storage time.  My gut level reaction,,, the oxide film at 5 volts
would work fine at five volts,,, but over time,,, the device may not like
going back to 50 volts all at once, without a current limited reforming time.

At 12:09 PM 3/8/00 -0500, you wrote:
>   I never thought about the reducing oxide film
>effect with lower voltages, it also means that the oxide is reduced (or
>even doesn't exist) when the equipment is powered off for quite some
>time?  I really don't know much about i


'Grif'   N7IVS

</x-flowed>

2000\03\08@131715 by David VanHorn

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At 02:28 PM 3/8/00 +0200, Roland Andrag wrote:
>Hello Everyone,
>
>I have just (with somewhat of a shock) found out that electrolytic caps are
>rated for only 2000 to 7000 hours of operation.  These ratings seem to be at
>high temperatures, but nonetheless they make me feel very uncomfortable
>about using them.  Is this some unspoken rule that somehow passed me by?

Don't let it scare you TOO much.

Jim Williams has a nice formula for this, that is darned accurate, but in
general terms, every 10 degrees C you take off the cap, doubles it's life.
A typical garbage electrolytic is 2000 hours at 85C, so roughly 4000 hours
at 75, 8000 at 65, 16000 at 55, 32000 at 45, 64000 at 35 (where I generally
figure my designs will operate)

This is correlated by my repair experience were most failures are traceable
to failed electrolytics, especially in anything that runs hot. Other parts
fail too, but ask anyone who repairs computer monitors or terminals, or
power supplies, or TVs (all use electrolytics at elevated temperatures, and
moderate to high currents)

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2000\03\08@132131 by David VanHorn

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part 0 82 bytes
ttachment converted: birth:Re- [OT] Short life on electrol (MiME/CSOm) (00007593)

2000\03\08@132544 by David VanHorn

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At 12:09 PM 3/8/00 -0500, Wagner Lipnharski wrote:
\ I never thought about the reducing oxide film
>effect with lower voltages, it also means that the oxide is reduced (or
>even doesn't exist) when the equipment is powered off for quite some
>time?  I really don't know much about it.
>Wagner


True, though you usually see it only on very old caps.
It may be a situation where ALL will eventually show the problem, but some
show it sooner.

In repairing old radios (paper cap days) you want to apply voltage very
slowly, and let the caps re-form if they will, to preserve the original
parts.  I do this with all high voltage caps I use, with a current limited
0-400V bench supply.

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2000\03\08@160615 by paulb

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David VanHorn wrote:

> running an electrolytic at voltages very much lower than it's rating
> can cause the forming process to somewhat reverse itself, resulting in
> a lower effective capacitance value.

 Lower?
--
 Cheers,
       Paul B.

2000\03\08@161448 by David VanHorn

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At 08:05 AM 3/9/00 +1100, Paul B. Webster VK2BZC wrote:
>David VanHorn wrote:
>
>> running an electrolytic at voltages very much lower than it's rating
>> can cause the forming process to somewhat reverse itself, resulting in
>> a lower effective capacitance value.
>
>  Lower?

That's what they told me.  "They go to sleep, and stop being capacitors".

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2000\03\08@192816 by Russell McMahon

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Lots of opinions on this I see.
Here's what I understand  (*but then, I may be wrong :-) )
I base my design decisions on this information :-)


1.    Electrolytic capacitors are lifetime rated at their maximum design
temperature.
As noted by others, lifetimes will approximately double for every 10 degrees
Celsius / kelvins drop below this temperature.
eg Lifetime = (Manufacturers stated lifetime) x 2^( (Trated - Tactual) /
10 )
eg 85 Celsius capacitor
35 Celsius working
2,000 hour rated
Actual lifetime = 2000 x 2^(85-35)/10) = 64,000 hours = 8 years

In practice it's not exactly double per 10 degrees C and manufacturers
provide a graph of lifetime versus temperature.

2.    Electrolytics operated at high temperature will die MUCH FASTER if the
power is OFF !!!!
The electrolyte dries out. Manufacturers provide a rating figure on this
too.
AFAIR an 85C cap will die in about 10% of its lifetime if run at 85C with
power off !!!!!!!!!!!!!

3.    Electrolytic capacitors are best run at voltages below but near their
rated voltage (rather than well below their rated voltage) , all things
being equal. It may be that other factors such as ESR, ripple current rating
etc lead you to other conditions but if these are adequate then it is better
to use a 10V cap for a 5V supply than a 50V cap for a 5 V supply.

General:
- Self heating due to eg ripple current must be taken into account.
- Ripple current specs must be observed to achieve rated lifetimes.
- Avoid polarity reversal
- Most cheap ecaps are rated at 85C but remember that 105C rated caps exist.
These are dearer but may make a vast difference to lifetimes in high ripple
and/or high temperature applications.


regards



     Russell McMahon
_____________________________

>From other worlds - http://www.easttimor.com
                               http://www.sudan.com

What can one man* do?
Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/

(* - or woman, child or internet enabled intelligent entity :-))


{Original Message removed}

2000\03\08@211144 by Dan Michaels

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Interesting thread. I recall once reading that aluminum
electrolytic caps have, to a certain extent, the ability
to resurrect themselves after they have been hit with
large "overvoltages", like ESD - eg, 5KV. Supposedly,
the aluminum oxide layer can rejuvenate, even after some
damage. Apparently doesn't work for tantalums, which don't
have the oxide layer.

Any additional experience/enlightenment along this line?
Like how much damage can they take, etc?

- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================

>
>{Original Message removed}

2000\03\09@005620 by Glenn Golden

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In a nut shell

1.)  Heat kills.

2.) Use caps. rated above but near operating voltage, the capacitance is
     less than rated at lower voltages.

3.)  Caps. on the shelf will not last as long as caps. in use.
      The electrolyte dries up.

2000\03\09@011348 by David VanHorn

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At 10:46 PM 3/8/00 -0700, Glenn Golden wrote:
>In a nut shell
>
>1.)  Heat kills.

Current kills too, (because of heat)   The equation by Jim Williams takes
into account the part ratings, Temperature, ESR, current, (and a few more
terms, but I forget)

Look in the linear tech apps for it, he and Bob Pease have a special place
in my bookshelf, next to AofE.

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2000\03\09@014810 by Nigel Goodwin

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In message <.....4.0.1.20000308131038.00fa6ca0KILLspamspam@spam@mail.cedar.net>, David VanHorn
<dvanhornspamKILLspamCEDAR.NET> writes
>Jim Williams has a nice formula for this, that is darned accurate, but in
>general terms, every 10 degrees C you take off the cap, doubles it's life.
>A typical garbage electrolytic is 2000 hours at 85C, so roughly 4000 hours
>at 75, 8000 at 65, 16000 at 55, 32000 at 45, 64000 at 35 (where I generally
>figure my designs will operate)
>
>This is correlated by my repair experience were most failures are traceable
>to failed electrolytics, especially in anything that runs hot. Other parts
>fail too, but ask anyone who repairs computer monitors or terminals, or
>power supplies, or TVs (all use electrolytics at elevated temperatures, and
>moderate to high currents)

The biggest capacitor failure is in satellite receivers, most have now
switched to 105 degree versions, and we only keep 105 degree ones as
replacements for use in everything we repair!.
--

Nigel.

       /--------------------------------------------------------------\
       | Nigel Goodwin   | Internet : .....nigelgKILLspamspam.....lpilsley.demon.co.uk     |
       | Lower Pilsley   | Web Page : http://www.lpilsley.demon.co.uk |
       | Chesterfield    | Official site for Shin Ki and New Spirit   |
       | England         |                 Ju Jitsu                   |
       \--------------------------------------------------------------/

2000\03\09@015648 by David VanHorn

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>The biggest capacitor failure is in satellite receivers, most have now
>switched to 105 degree versions, and we only keep 105 degree ones as
>replacements for use in everything we repair!.

I use only 105 degree units in new designs too, the price difference isn't
that large.

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2000\03\09@021239 by Roland Andrag

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Thanks for all the great replies!! Someone (David VanHorn?) has made
reference to Jim Williams - which book were you referring to (could you give
a more complete reference) - sounds like interesting reading...

Thanks
Roland

2000\03\09@032518 by Graham North

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I have a satellite receiver which does not work, I have tried but can not
find the problem.

How can I tell if it's the caps?

Cheers

Graham



       The biggest capacitor failure is in satellite receivers, most have
now
       switched to 105 degree versions, and we only keep 105 degree ones as
       replacements for use in everything we repair!.
       --

       Nigel.

2000\03\09@080942 by Tom Handley

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  Dan, this is a good thread. I had to revisit the subject when my old
Mag Innovision 17" monitor died a couple of years ago. It turned out that
electrolytic caps spec'd at 85C died taking out several components from the
H.O.T. to the flyback transformer... Talking with Mag confirmed the problem
and I got the replacement parts with 105C caps...

  The "rehealing" feature with electrolytics relates to the working
electrolyte in that any faults in the oxide layer will be repaired by
further anodization. This is a factor is the design of the cap.

  "Self-Healing" refers to metallized caps where a partial discharge
results in a localized failure of the dielectric which burns away the
metallized electrode effectively isolating the fault.

  Someone mentioned "reforming" electrolytics. I had not considered this
to be a problem but, after `blowing the dust off' ITT's "Reference Data for
Radio Engineers", I ran across the following:

  "Conventional aluminum electrolytic capacitors which have gone 6 months
or more without voltage applied may have to be reformed." A DC source at the
rated voltage with a 1.5K internal resistance for caps with a rated voltage
exceeding 100V or 150 ohms for <=100V must be applied for one hour after the
cap reaches it's rated voltage +/- 3%. The cap is then discharged through a
resistor of 1ohm/V.

  I would first check with the cap vendor to see what the shelf-life is in
this `day and age', and what, if any, `reforming' procedure is required.
Still, it's something to think about if you have a bunch of `ancient'
electrolytics laying around and you are experimenting for home use.

  - Tom

At 07:12 PM 3/8/00 -0700, Dan Michaels wrote:
{Quote hidden}

------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

2000\03\09@120726 by David VanHorn

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At 08:23 AM 3/9/00 +0000, Graham North wrote:
>I have a satellite receiver which does not work, I have tried but can not
>find the problem.
>
>How can I tell if it's the caps?


Your first clue would be if any have exploded, bulged, or ruptured their
tops.
After that, you'll likely need a schematic, and a meter at least, to track
down the problem
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2000\03\09@124713 by Dan Michaels

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Tom wrote:

>   The "rehealing" feature with electrolytics relates to the working
>electrolyte in that any faults in the oxide layer will be repaired by
>further anodization. This is a factor is the design of the cap.
>
>   "Self-Healing" refers to metallized caps where a partial discharge
>results in a localized failure of the dielectric which burns away the
>metallized electrode effectively isolating the fault.
>

So, it is reasonable to think that a cap *blasted by an ESD bolt*
can possibly "reheal" by reforming its oxide layer, or may
"self-heal" with the charge blasting the electrode away in a local
area, but leaving intact the rest of the cap surface. (I'm not sure
if your reference to "s-h" & metallized caps applies to aluminum
electrolytics).

I got onto this a few years ago, when consulting with a company
that was using 6805 embedded controllers in industrial icemaker
machines. A really bad ESD, EMI, and inductive switching transient
environment. The controllers were constantly latching up (the
orig design had NO protection on the sense lines at all - would you
believe!). The contractor redesigned the controllers by adding
pi-filters to the sense lines, consisting of 10uF/25v alum
electrolytic right on the "external" pin, then 10K resistor, and
finally .1 uF bypass at the uC pin.

We did some inhouse ESD tests using a 5KV Zap gun, and I was
amazed to discover that the little 25v electrolytics weren't
completely blown off the boards. Leakage increased into the
caps temporarily, but this seemed to diminish after a while.
Thus, I got onto the healing bit.

I also discovered that the small lead spacing on the caps acted
as a spark gap, but still the caps must have been getting blasted
pretty good. All in all, pretty amazing.

Thanks,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom

2000\03\09@134633 by Tom Handley

picon face
At 10:45 AM 3/9/00 -0700, Dan Michaels wrote:
>So, it is reasonable to think that a cap *blasted by an ESD bolt*
>can possibly "reheal" by reforming its oxide layer, or may
>"self-heal" with the charge blasting the electrode away in a local
>area, but leaving intact the rest of the cap surface. (I'm not sure
>if your reference to "s-h" & metallized caps applies to aluminum
>electrolytics).

  Dan, "Self-Healing" only applies to metallized caps (with metallized
electrodes), not electrolytics. I brought that up to prevent confusion
with the "rehealing" property of electrolytics.

  - Tom

>I wrote:
>>   The "rehealing" feature with electrolytics relates to the working
>>electrolyte in that any faults in the oxide layer will be repaired by
>>further anodization. This is a factor is the design of the cap.
>>
>>   "Self-Healing" refers to metallized caps where a partial discharge
>>results in a localized failure of the dielectric which burns away the
>>metallized electrode effectively isolating the fault.


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

2000\03\09@164952 by John Orhan

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Hi all,
I am searching for a good hi fi power output stage circuit around the 50 -
100watt mark having foolishely volenteered to help a good friend of mine
with his audiophilia problem . Can anyone suggest a good site for such
things or a known good circuit?? This will save months of angst.

                               Sincerely       John

               {Original Message removed}

2000\03\09@170028 by David VanHorn

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At 08:48 AM 3/10/00 +1100, John Orhan wrote:
>Hi all,
>I am searching for a good hi fi power output stage circuit around the 50 -
>100watt mark having foolishely volenteered to help a good friend of mine
>with his audiophilia problem . Can anyone suggest a good site for such
>things or a known good circuit?? This will save months of angst.


There is no known cure for audiophilia.

Unfortunately, they tend to ignore sound engineering, and go with the "it's
more expensive, so it must be better" approach.. :-P
I lost the link, but I had a site selling a 3 Meter speaker cable for
$7000.00

For my money, an LM-12 is pretty hard to beat, and you can connect it as a
voltage to current converter, and drive the speakers that way, eliminating
the effects of the speaker wire.


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2000\03\09@180522 by Gennette Bruce

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       -----Original Message-----
       From:   David VanHorn [SMTP:EraseMEdvanhornspam_OUTspamTakeThisOuTCEDAR.NET]
       Sent:   Friday, 10 March 2000 6:41
       To:     PICLISTspamspam_OUTMITVMA.MIT.EDU
       Subject:        Re: [OT] Short life on electrolytic caps

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       At 08:23 AM 3/9/00 +0000, Graham North wrote:
       >I have a satellite receiver which does not work, I have tried but
can not
       >find the problem.
       >
       >How can I tell if it's the caps?


       Your first clue would be if any have exploded, bulged, or ruptured
their
       tops.
       After that, you'll likely need a schematic, and a meter at least, to
track
       down the problem

You forgot colour change - quiet or failed Sanyo TV sound was always easy to
fix, you just looked for the grey cap in amoungest the pink ones.  The dried
out caps heated up and changed the wrapper colour as they failed.

Bye.

2000\03\09@181543 by David VanHorn

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>You forgot colour change - quiet or failed Sanyo TV sound was always easy to
>fix, you just looked for the grey cap in amoungest the pink ones.  The dried
>out caps heated up and changed the wrapper colour as they failed.


Nice of them to do that, but it's mostly peculiar to that brand.
The ones I've seen don't change color until they are showing many other
symptoms.
(like fragmentation)
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2000\03\09@191401 by Kev

picon face
Cap Meter or ESR meter will help find failed/ marginal caps.  There is even
a PIC project to build a cap meter, just don't have the address handy.

Kev
HKC Inc

>         >
>         >How can I tell if it's the caps?
>
>
>         Your first clue would be if any have exploded, bulged, or ruptured
> their
>         tops.
>         After that, you'll likely need a schematic, and a meter at least,
to
> track
>         down the problem
>
> You forgot colour change - quiet or failed Sanyo TV sound was always easy
to
> fix, you just looked for the grey cap in amoungest the pink ones.  The
dried
> out caps heated up and changed the wrapper colour as they failed.
>
> Bye.
>

2000\03\09@200802 by Joe Dudas

picon face
   http://redrival.com/mcgahee/

That addy will get you to teh projects page

Joe
----- Original Message -----
From: "Kev" <@spam@KKloppKILLspamspamEROLS.COM>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Thursday, March 09, 2000 4:12 PM
Subject: Re: [OT] Short life on electrolytic caps


> Cap Meter or ESR meter will help find failed/ marginal caps.  There is
even
> a PIC project to build a cap meter, just don't have the address handy.
>
> Kev
> HKC Inc
>
> >         >
> >         >How can I tell if it's the caps?
> >
> >
> >         Your first clue would be if any have exploded, bulged, or
ruptured
> > their
> >         tops.
> >         After that, you'll likely need a schematic, and a meter at
least,
> to
> > track
> >         down the problem
> >
> > You forgot colour change - quiet or failed Sanyo TV sound was always
easy
> to
> > fix, you just looked for the grey cap in amoungest the pink ones.  The
> dried
> > out caps heated up and changed the wrapper colour as they failed.
> >
> > Bye.
> >

2000\03\10@015148 by Nigel Goodwin

flavicon
picon face
In message <6621F2E12035D311B02208002BC33C593B1BB3@LANDUK1>, Graham
North <RemoveMEgraham.northTakeThisOuTspamLANDINST.COM> writes
>I have a satellite receiver which does not work, I have tried but can not
>find the problem.
>
>How can I tell if it's the caps?

Stick a scope on the PSU outputs, and measure the ripple - it should be
fairly low on all the outputs. Obviously 1 volt ripple on a 30 volt rail
isn't too bad, but 1 volt ripple on a 5 volt rail is much too high, it's
normally pretty obvious which ones are duff. You also get problems with
coupling capacitors drying out as well, you really need a circuit to
follow the signal path to find those.
--

Nigel.

       /--------------------------------------------------------------\
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       \--------------------------------------------------------------/

2000\03\10@044906 by paulb

flavicon
face
David VanHorn wrote:

> Your first clue would be if any have exploded, bulged, or ruptured
> After that, you'll likely need a schematic, and a meter at least, to
> track down the problem

 Schematic?  Now *here's* a serious sort of sense of humour! :))
--
 Cheers,
       Paul B.

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