Anyone read anywhere what the failure mechanism is for solid dielectric caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel like
a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one choke,
and one cap. On the 80Hz channel, this cap was a 3u3 tantalum bullet, and it
was 2k leaky. Why ? The device is under no voltage stress at all in this
position, being subject to low signal levels only. I wonder if it's some
kind of internal 'growth' like the dreaded tin whiskers, which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band disappeared.

Arfa

"Arfa Daily" wrote in message
...
Anyone read anywhere what the failure mechanism is for solid dielectric
caps of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel
like a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke, and one cap. On the 80Hz channel, this cap was a 3u3 tantalum
bullet, and it was 2k leaky. Why ? The device is under no voltage stress
at all in this position, being subject to low signal levels only. I wonder
if it's some kind of internal 'growth' like the dreaded tin whiskers,
which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band disappeared.

Arfa


Tantalums have kind of a bad reputation for shorting, and that's been my
experience. Not really seen them leaky or open.

The scratchy sound of the pot is typical of DC leakage in such a circuit.
Can make a volume pot or similar sound "dirty" or make woofers go "whoomp"
when the control is moved.

But then you know this, yes? I know you have loads of experience with this
stuff.

I got the "whoomp - whoomp" in a Yamaha receiver the other day - a bad
muting transistor put DC on the volume control.

Mark Z.

Arfa Daily wrote in message
...
Anyone read anywhere what the failure mechanism is for solid dielectric
caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel
like
a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke,
and one cap. On the 80Hz channel, this cap was a 3u3 tantalum bullet, and
it
was 2k leaky. Why ? The device is under no voltage stress at all in this
position, being subject to low signal levels only. I wonder if it's some
kind of internal 'growth' like the dreaded tin whiskers, which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band disappeared.

Arfa




I only remember s/c failures. Is there meatalisation either side of a narrow
edge? and then metalisation creep over the edge or into a crack ala this
mechanism
http://www.era.co.uk/news/rfa_feature_07b.asp
a useful study on failure mechansim of otherwise trouble free capacitors

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm

"Mark Zacharias" wrote in message
...
"Arfa Daily" wrote in message
...
Anyone read anywhere what the failure mechanism is for solid dielectric
caps of the tantalum variety ? In my experience, no matter what the
value, working voltage, or format (bead, bullet or box), they always seem
to fail leaky. Not open or short (well, very occasionally short). Just
leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd
problem in that when the 80Hz slider in the graphic was advanced in the
'boost' direction, the audio suddenly went very distorted, and then
disappeared. There was also a slight 'scratchiness' to this pot, which
did not feel like a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke, and one cap. On the 80Hz channel, this cap was a 3u3 tantalum
bullet, and it was 2k leaky. Why ? The device is under no voltage stress
at all in this position, being subject to low signal levels only. I
wonder if it's some kind of internal 'growth' like the dreaded tin
whiskers, which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band
disappeared.

Arfa


Tantalums have kind of a bad reputation for shorting, and that's been my
experience. Not really seen them leaky or open.

The scratchy sound of the pot is typical of DC leakage in such a circuit.
Can make a volume pot or similar sound "dirty" or make woofers go "whoomp"
when the control is moved.

But then you know this, yes? I know you have loads of experience with this
stuff.


Indeed yes, Mark. That was what gave the clue that it was going to be the
cap, and caused me to unsolder it, and reach for the meter ... :-)



I got the "whoomp - whoomp" in a Yamaha receiver the other day - a bad
muting transistor put DC on the volume control.

Mark Z.

I fear that such knowledge, that we were taught as young techs by others
much older and wiser than ourselves, is doomed to be conscripted to the
'lost' pile, as we expire one by one ... :-(

Arfa

Mark Zacharias wrote in message
...
"Arfa Daily" wrote in message
...
Anyone read anywhere what the failure mechanism is for solid dielectric
caps of the tantalum variety ? In my experience, no matter what the
value,
working voltage, or format (bead, bullet or box), they always seem to
fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd
problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel
like a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke, and one cap. On the 80Hz channel, this cap was a 3u3 tantalum
bullet, and it was 2k leaky. Why ? The device is under no voltage stress
at all in this position, being subject to low signal levels only. I
wonder
if it's some kind of internal 'growth' like the dreaded tin whiskers,
which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band
disappeared.

Arfa


Tantalums have kind of a bad reputation for shorting, and that's been my
experience. Not really seen them leaky or open.

The scratchy sound of the pot is typical of DC leakage in such a circuit.
Can make a volume pot or similar sound "dirty" or make woofers go "whoomp"
when the control is moved.

But then you know this, yes? I know you have loads of experience with this
stuff.

I got the "whoomp - whoomp" in a Yamaha receiver the other day - a bad
muting transistor put DC on the volume control.

Mark Z.


I misdirected myself , only last week, removing a perceived scratchy/worn
pot, that was fine, other than it had DC on it from a digital delay cct
fault.

"Arfa Daily" wrote in message
...
Anyone read anywhere what the failure mechanism is for solid dielectric
caps of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel
like a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke, and one cap. On the 80Hz channel, this cap was a 3u3 tantalum
bullet, and it was 2k leaky. Why ? The device is under no voltage stress
at all in this position, being subject to low signal levels only. I wonder
if it's some kind of internal 'growth' like the dreaded tin whiskers,
which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band disappeared.

Arfa


It seems to me that tants are notoriously intolerant of reverse voltage -
even at small signal levels!

These days ceramic chip capacitors can be found upto several uF (maybe even
10) that are small enough to substitute bead types, for larger values I'd be
tempted to go for high temp/low ESR aluminium types and maybe add a ceramic
chip SMD on the print side.

Mark Zacharias Inscribed thus:

"Arfa Daily" wrote in message
...
Anyone read anywhere what the failure mechanism is for solid
dielectric caps of the tantalum variety ? In my experience, no matter
what the value, working voltage, or format (bead, bullet or box),
they always seem to fail leaky. Not open or short (well, very
occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd
problem in that when the 80Hz slider in the graphic was advanced in
the 'boost' direction, the audio suddenly went very distorted, and
then disappeared. There was also a slight 'scratchiness' to this pot,
which did not feel like a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke, and one cap. On the 80Hz channel, this cap was a 3u3 tantalum
bullet, and it was 2k leaky. Why ? The device is under no voltage
stress at all in this position, being subject to low signal levels
only. I wonder if it's some kind of internal 'growth' like the
dreaded tin whiskers, which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band
disappeared.

Arfa


Tantalums have kind of a bad reputation for shorting, and that's been
my experience. Not really seen them leaky or open.

Thats been my experience too. I've seen them glow red hot and burst
like a volcano, spraying tiny red hot fragments all over. The
fragments burn for a second or so before dying out. Admittedly nearly
all that have done this have been bead types.

The scratchy sound of the pot is typical of DC leakage in such a
circuit. Can make a volume pot or similar sound "dirty" or make
woofers go "whoomp" when the control is moved.

But then you know this, yes? I know you have loads of experience with
this stuff.

I got the "whoomp - whoomp" in a Yamaha receiver the other day - a bad
muting transistor put DC on the volume control.

Mark Z.

--
Best Regards:
Baron.

"Arfa Daily" writes:

Anyone read anywhere what the failure mechanism is for solid dielectric caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Hmmmm. They must have "improved" them. Recall all those gum-drop
tantalums in Tek scopes that failed dead short across the power rails?

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel like
a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one choke,
and one cap. On the 80Hz channel, this cap was a 3u3 tantalum bullet, and it
was 2k leaky. Why ? The device is under no voltage stress at all in this
position, being subject to low signal levels only. I wonder if it's some
kind of internal 'growth' like the dreaded tin whiskers, which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band disappeared.

Arfa

(Samuel M. Goldwasser) wrote in
:

"Arfa Daily" writes:

Anyone read anywhere what the failure mechanism is for solid
dielectric caps of the tantalum variety ? In my experience, no matter
what the value, working voltage, or format (bead, bullet or box),
they always seem to fail leaky. Not open or short (well, very
occasionally short). Just leaky.

Hmmmm. They must have "improved" them. Recall all those gum-drop
tantalums in Tek scopes that failed dead short across the power rails?



Yes,I do,quite well. 8-)

--
Jim Yanik
jyanik
at
localnet
dot com

On Fri, 19 Mar 2010 02:24:18 -0000, "Arfa Daily"
put finger to keyboard and composed:

Anyone read anywhere what the failure mechanism is for solid dielectric caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

I've had one particular board where the same tantalum cap (bead) would
go leaky.

All other faults were dead shorts across a supply rail. I must have
replaced over a hundred of them (bead) in all manner of equipment. I
recall seeing one tantalum cap explode and catch fire like a match
head.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Sun, 21 Mar 2010 08:01:20 +1100, Franc Zabkar wrote:

On Fri, 19 Mar 2010 02:24:18 -0000, "Arfa Daily"
put finger to keyboard and composed:

Anyone read anywhere what the failure mechanism is for solid dielectric caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

I've had one particular board where the same tantalum cap (bead) would
go leaky.

What voltage across it? Maybe they're no good at near zero DC?


All other faults were dead shorts across a supply rail. I must have
replaced over a hundred of them (bead) in all manner of equipment. I
recall seeing one tantalum cap explode and catch fire like a match
head.

I've only seen them fail when reverse connected. Spectacularly in
one case with reverse connection on 24V battery -- high pitch bang
behind my back, when I turned around to look at the board and there
was the remains of the cap, standing on one leg, glowing red hot,
cooling off. No sign of the other leg or case...

Grant.
--
http://bugs.id.au/

"Grant" wrote in message
...
On Sun, 21 Mar 2010 08:01:20 +1100, Franc Zabkar
wrote:

On Fri, 19 Mar 2010 02:24:18 -0000, "Arfa Daily"
put finger to keyboard and composed:

Anyone read anywhere what the failure mechanism is for solid dielectric
caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to
fail
leaky. Not open or short (well, very occasionally short). Just leaky.

I've had one particular board where the same tantalum cap (bead) would
go leaky.

What voltage across it? Maybe they're no good at near zero DC?


All other faults were dead shorts across a supply rail. I must have
replaced over a hundred of them (bead) in all manner of equipment. I
recall seeing one tantalum cap explode and catch fire like a match
head.

I've only seen them fail when reverse connected. Spectacularly in
one case with reverse connection on 24V battery -- high pitch bang
behind my back, when I turned around to look at the board and there
was the remains of the cap, standing on one leg, glowing red hot,
cooling off. No sign of the other leg or case...

So far I've never seen one blow - only go leaky in small signal circuits.
Wherever possible I try to find a non-polarized cap (film or ceramic chip)
small enough to fit the space - that strategy never bounced a repair.

"ian field" wrote in
:


"Grant" wrote in message
...
On Sun, 21 Mar 2010 08:01:20 +1100, Franc Zabkar
wrote:

On Fri, 19 Mar 2010 02:24:18 -0000, "Arfa Daily"
put finger to keyboard and composed:

Anyone read anywhere what the failure mechanism is for solid
dielectric caps
of the tantalum variety ? In my experience, no matter what the
value, working voltage, or format (bead, bullet or box), they always
seem to fail
leaky. Not open or short (well, very occasionally short). Just
leaky.

I've had one particular board where the same tantalum cap (bead)
would go leaky.

What voltage across it? Maybe they're no good at near zero DC?


All other faults were dead shorts across a supply rail. I must have
replaced over a hundred of them (bead) in all manner of equipment. I
recall seeing one tantalum cap explode and catch fire like a match
head.

I've only seen them fail when reverse connected. Spectacularly in
one case with reverse connection on 24V battery -- high pitch bang
behind my back, when I turned around to look at the board and there
was the remains of the cap, standing on one leg, glowing red hot,
cooling off. No sign of the other leg or case...

So far I've never seen one blow - only go leaky in small signal
circuits. Wherever possible I try to find a non-polarized cap (film or
ceramic chip) small enough to fit the space - that strategy never
bounced a repair.




In TEK scopes,they were often shorted,and were used in PS decoupling
circuits ALL over the scope.
Sometimes,I could see a tiny pinhole in the epoxy coating.
I've seen them burned,too,even just the leads remaining,sticking out of the
PCB pads.

IMO,it's usually OV spikes or polarity reversals that take out tantalums.
Or manufacturing defects.

--
Jim Yanik
jyanik
at
localnet
dot com

Jim Yanik wrote:

"ian field" wrote in
:


"Grant" wrote in message
. ..

On Sun, 21 Mar 2010 08:01:20 +1100, Franc Zabkar
wrote:


On Fri, 19 Mar 2010 02:24:18 -0000, "Arfa Daily"
put finger to keyboard and composed:


Anyone read anywhere what the failure mechanism is for solid
dielectric caps
of the tantalum variety ? In my experience, no matter what the
value, working voltage, or format (bead, bullet or box), they always
seem to fail
leaky. Not open or short (well, very occasionally short). Just
leaky.

I've had one particular board where the same tantalum cap (bead)
would go leaky.

What voltage across it? Maybe they're no good at near zero DC?


All other faults were dead shorts across a supply rail. I must have
replaced over a hundred of them (bead) in all manner of equipment. I
recall seeing one tantalum cap explode and catch fire like a match
head.

I've only seen them fail when reverse connected. Spectacularly in
one case with reverse connection on 24V battery -- high pitch bang
behind my back, when I turned around to look at the board and there
was the remains of the cap, standing on one leg, glowing red hot,
cooling off. No sign of the other leg or case...

So far I've never seen one blow - only go leaky in small signal
circuits. Wherever possible I try to find a non-polarized cap (film or
ceramic chip) small enough to fit the space - that strategy never
bounced a repair.





In TEK scopes,they were often shorted,and were used in PS decoupling
circuits ALL over the scope.
Sometimes,I could see a tiny pinhole in the epoxy coating.
I've seen them burned,too,even just the leads remaining,sticking out of the
PCB pads.

IMO,it's usually OV spikes or polarity reversals that take out tantalums.
Or manufacturing defects.

Oh I love tantalums. "Ashes to ashes, dust to dust"

"ian field" wrote in message
...

"Grant" wrote in message
...
On Sun, 21 Mar 2010 08:01:20 +1100, Franc Zabkar
wrote:

On Fri, 19 Mar 2010 02:24:18 -0000, "Arfa Daily"
put finger to keyboard and composed:

Anyone read anywhere what the failure mechanism is for solid dielectric
caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to
fail
leaky. Not open or short (well, very occasionally short). Just leaky.

I've had one particular board where the same tantalum cap (bead) would
go leaky.

What voltage across it? Maybe they're no good at near zero DC?


All other faults were dead shorts across a supply rail. I must have
replaced over a hundred of them (bead) in all manner of equipment. I
recall seeing one tantalum cap explode and catch fire like a match
head.

I've only seen them fail when reverse connected. Spectacularly in
one case with reverse connection on 24V battery -- high pitch bang
behind my back, when I turned around to look at the board and there
was the remains of the cap, standing on one leg, glowing red hot,
cooling off. No sign of the other leg or case...

So far I've never seen one blow - only go leaky in small signal circuits.
Wherever possible I try to find a non-polarized cap (film or ceramic chip)
small enough to fit the space - that strategy never bounced a repair.


How interesting. Seems that lots of people *have* seen them go short and
even explode, but my experience of them really has been predominantly that
of them going leaky, whereas my experience of proper wet electros, has been
the exact reverse. Now here's a curve ball then. Most of the people that
have a lot of experience of them going short, seem to be leftpondians.
Myself and Ian, are both 'rights' ...

Arfa

Arfa Daily Inscribed thus:

How interesting. Seems that lots of people *have* seen them go short
and even explode, but my experience of them really has been
predominantly that of them going leaky, whereas my experience of
proper wet electros, has been the exact reverse. Now here's a curve
ball then. Most of the people that have a lot of experience of them
going short, seem to be leftpondians. Myself and Ian, are both
'rights' ...

Arfa

Interesting observation ! Since I'm also on the right side of the pond.

--
Best Regards:
Baron.

I recall hearing a long time ago that tantalum caps do in fact tend to
grow metallic whiskers inside, between the plates, which ultimately
bridge the cap. Whether it's tantalum or some other metal used in
construction, it is a poor conductor, and in a power supply, will
immediately burn out and the cap will return to normal. If the cap is
left for a long long time without power applied, the bridge can become
quite substantial, and the heat generated next time power is applied
can blow the cap apart. I remember the moral of the story is that
tantalum caps are good only for decoupling and power filtering, where
there is guaranteed to be sufficient current to deal with the shorts.
They are attractive for low signal applications because of their size,
but I've never used them for the above reasons.

Now, is any of this true? I have no idea. But it would account for Ta
caps in signal applications failing in a leaky manner.

On Mar 18, 10:24*pm, "Arfa Daily" wrote:
Anyone read anywhere what the failure mechanism is for solid dielectric caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel like
a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one choke,
and one cap. On the 80Hz channel, this cap was a 3u3 tantalum bullet, and it
was 2k leaky. Why ? The device is under no voltage stress at all in this
position, being subject to low signal levels only. I wonder if it's some
kind of internal 'growth' like the dreaded tin whiskers, which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band disappeared..

Arfa

wrote in message
...
I recall hearing a long time ago that tantalum caps do in fact tend to
grow metallic whiskers inside, between the plates, which ultimately
bridge the cap. Whether it's tantalum or some other metal used in
construction, it is a poor conductor, and in a power supply, will
immediately burn out and the cap will return to normal. If the cap is
left for a long long time without power applied, the bridge can become
quite substantial, and the heat generated next time power is applied
can blow the cap apart. I remember the moral of the story is that
tantalum caps are good only for decoupling and power filtering, where
there is guaranteed to be sufficient current to deal with the shorts.
They are attractive for low signal applications because of their size,
but I've never used them for the above reasons.

Now, is any of this true? I have no idea. But it would account for Ta
caps in signal applications failing in a leaky manner.

On Mar 18, 10:24 pm, "Arfa Daily" wrote:
Anyone read anywhere what the failure mechanism is for solid dielectric
caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel
like
a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke,
and one cap. On the 80Hz channel, this cap was a 3u3 tantalum bullet, and
it
was 2k leaky. Why ? The device is under no voltage stress at all in this
position, being subject to low signal levels only. I wonder if it's some
kind of internal 'growth' like the dreaded tin whiskers, which causes it ?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band disappeared.

Arfa

some useful info here
http://my.execpc.com/~endlr/reliability.html

Baron wrote:
Arfa Daily Inscribed thus:

How interesting. Seems that lots of people *have* seen them go short
and even explode, but my experience of them really has been
predominantly that of them going leaky, whereas my experience of
proper wet electros, has been the exact reverse. Now here's a curve
ball then. Most of the people that have a lot of experience of them
going short, seem to be leftpondians. Myself and Ian, are both
'rights' ...

Arfa

Interesting observation ! Since I'm also on the right side of the pond.

Are we not all on the right side of the pond??

I dont think there IS a wrong side

On Sun, 21 Mar 2010 23:44:33 +0100, Sjouke Burry wrote:

Baron wrote:
Arfa Daily Inscribed thus:

How interesting. Seems that lots of people *have* seen them go short
and even explode, but my experience of them really has been
predominantly that of them going leaky, whereas my experience of
proper wet electros, has been the exact reverse. Now here's a curve
ball then. Most of the people that have a lot of experience of them
going short, seem to be leftpondians. Myself and Ian, are both
'rights' ...

Arfa

Interesting observation ! Since I'm also on the right side of the pond.

Are we not all on the right side of the pond??

I dont think there IS a wrong side

'Cept for the land down under

Grant.

Grant wrote:
cut
Interesting observation ! Since I'm also on the right side of the pond.

Are we not all on the right side of the pond??

I dont think there IS a wrong side

'Cept for the land down under

Grant.
Thats not the wrong side, thats the bottom side ......

"Sjouke Burry" wrote in message
...
Baron wrote:
Arfa Daily Inscribed thus:

How interesting. Seems that lots of people *have* seen them go short
and even explode, but my experience of them really has been
predominantly that of them going leaky, whereas my experience of
proper wet electros, has been the exact reverse. Now here's a curve
ball then. Most of the people that have a lot of experience of them
going short, seem to be leftpondians. Myself and Ian, are both
'rights' ...

Arfa

Interesting observation ! Since I'm also on the right side of the pond.

Are we not all on the right side of the pond??

I dont think there IS a wrong side

Oh dear ! That's right as in not left ... d;-}

Arfa

"N_Cook" wrote in message
...

On Mar 18, 10:24 pm, "Arfa Daily" wrote:
Anyone read anywhere what the failure mechanism is for solid dielectric
caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to
fail
leaky. Not open or short (well, very occasionally short). Just leaky.

Example. Today, I had a Mesa Boogie combo cross my bench. Very odd
problem
in that when the 80Hz slider in the graphic was advanced in the 'boost'
direction, the audio suddenly went very distorted, and then disappeared.
There was also a slight 'scratchiness' to this pot, which did not feel
like
a bad or dirty track.

When I got the graphic pots board out, it was actually quite a simple
affair, with each of the 6 bands having just a pot, one resistor, one
choke,
and one cap. On the 80Hz channel, this cap was a 3u3 tantalum bullet, and
it
was 2k leaky. Why ? The device is under no voltage stress at all in this
position, being subject to low signal levels only. I wonder if it's some
kind of internal 'growth' like the dreaded tin whiskers, which causes it
?

A new cap (used a 3u3 tant bead that I had in stock) restored normal
operation of the equaliser, and all scratchiness in that band
disappeared.

Arfa


wrote in message
...
I recall hearing a long time ago that tantalum caps do in fact tend to
grow metallic whiskers inside, between the plates, which ultimately
bridge the cap. Whether it's tantalum or some other metal used in
construction, it is a poor conductor, and in a power supply, will
immediately burn out and the cap will return to normal. If the cap is
left for a long long time without power applied, the bridge can become
quite substantial, and the heat generated next time power is applied
can blow the cap apart. I remember the moral of the story is that
tantalum caps are good only for decoupling and power filtering, where
there is guaranteed to be sufficient current to deal with the shorts.
They are attractive for low signal applications because of their size,
but I've never used them for the above reasons.

Now, is any of this true? I have no idea. But it would account for Ta
caps in signal applications failing in a leaky manner.


Indeed it would ...


some useful info here
http://my.execpc.com/~endlr/reliability.html



Very interesting

Arfa

"Arfa Daily" wrote in message
...

"Sjouke Burry" wrote in message
...
Baron wrote:
Arfa Daily Inscribed thus:

How interesting. Seems that lots of people *have* seen them go short
and even explode, but my experience of them really has been
predominantly that of them going leaky, whereas my experience of
proper wet electros, has been the exact reverse. Now here's a curve
ball then. Most of the people that have a lot of experience of them
going short, seem to be leftpondians. Myself and Ian, are both
'rights' ...

Arfa

Interesting observation ! Since I'm also on the right side of the pond.

Are we not all on the right side of the pond??

I dont think there IS a wrong side

Oh dear ! That's right as in not left ... d;-}

Arfa


Who's left?

"ian field" wrote in message
...

"Arfa Daily" wrote in message
...

"Sjouke Burry" wrote in message
...
Baron wrote:
Arfa Daily Inscribed thus:

How interesting. Seems that lots of people *have* seen them go short
and even explode, but my experience of them really has been
predominantly that of them going leaky, whereas my experience of
proper wet electros, has been the exact reverse. Now here's a curve
ball then. Most of the people that have a lot of experience of them
going short, seem to be leftpondians. Myself and Ian, are both
'rights' ...

Arfa

Interesting observation ! Since I'm also on the right side of the
pond.

Are we not all on the right side of the pond??

I dont think there IS a wrong side

Oh dear ! That's right as in not left ... d;-}

Arfa


Who's left?


Someone said that Elvis had left the building ...

Arfa

Sjouke Burry Inscribed thus:

Baron wrote:
Arfa Daily Inscribed thus:

How interesting. Seems that lots of people *have* seen them go short
and even explode, but my experience of them really has been
predominantly that of them going leaky, whereas my experience of
proper wet electros, has been the exact reverse. Now here's a curve
ball then. Most of the people that have a lot of experience of them
going short, seem to be leftpondians. Myself and Ian, are both
'rights' ...

Arfa

Interesting observation ! Since I'm also on the right side of the
pond.

Are we not all on the right side of the pond??

I dont think there IS a wrong side

I belive I must agree ! ;-)

--
Best Regards:
Baron.

On Sun, 21 Mar 2010 09:01:00 +1100, Grant put finger
to keyboard and composed:

On Sun, 21 Mar 2010 08:01:20 +1100, Franc Zabkar wrote:

On Fri, 19 Mar 2010 02:24:18 -0000, "Arfa Daily"
put finger to keyboard and composed:

Anyone read anywhere what the failure mechanism is for solid dielectric caps
of the tantalum variety ? In my experience, no matter what the value,
working voltage, or format (bead, bullet or box), they always seem to fail
leaky. Not open or short (well, very occasionally short). Just leaky.

I've had one particular board where the same tantalum cap (bead) would
go leaky.

What voltage across it? Maybe they're no good at near zero DC?

It was in a video mixer board. I can't remember its exact function,
but it was somewhere in the signal path. The board had analogue and
TTL components, so the voltages were +5V, +12V, and -12V, IIRC.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.