Tantalum caps.

[Frank Miles]

In article <MPG.1a79a982cc75a507989c17@192.168.42.131>,
Dr. Anton.T. Squeegee <SpammersArePondScum@dev.null> wrote:

In article <100u2kvskpbroc8@corp.supernews.com>, wd5jfr@oklahoma.net
says...

<snippety

from my personal stuff purchased new. One example is a MGA Mitsubishi rear
projection TV that operated flawlessly for nearly 20 years of daily use.
Most of my test equipment comes from hamfests and is surplus after becoming
obsolete and non-operative in less than 20 years. That leads me to wonder
what the real story is behind tantalum capacitors. What do the experts have
to say?

The ONLY problems I've ever had with tantalums are where:

(1) The part was defective from the manufacturer.

(2) The voltage rating was consistently exceeded.

(3) The thing was installed backwards (reverse polarity).

I have no less than five Tektronix O-scopes here, all vintage
late-70's to mid-80's. This means not one of them is less than 20 years
old. They all use lots of tantalums, and they all work great, but then
again Tek was (in those days) proud of what they put out, and was most
definitely engineer-driven (which means at least a 20% 'fudge factor'
built into everything they made).

Tantalum caps are very stable and durable, but they are much more
costly than aluminum types. In consumer electronics, the manufacturers
will try to shave every penny they can off the cost of the design, often
contrary to good common (engineering) sense.

Such considerations are (usually) not so critical when it comes to
non-consumer stuff.

Tektronix was, during that time, strongly discouraging all new designs from
using tantalums. IIRC they had been taken to court over a case in which
a 465 'scope (the original, not the plastic follow-ons) had spontaneously
ignited and had resulted in an expensive fire. Forensics revealed that
a tantalum power-supply bypass cap had started the conflagration. The
drive to reduce tantalum usage was driven primarily by this liability issue,
more than component cost. If you wanted to use a tantalum, you had to
justify its usage to the component/design review committees -- which wasn't
difficult if you had good reasons and your design was solid.

-frank
(ex-Tekie)
--

 

[ddwyer]

In article <5f5159fa.0401212325.d64168f@posting.google.com>, OK1SIP
<remove_ok1sip@atlas.cz> writes

Hi all,
tantalum caps seem to be too expensive for consumer-grade equipment.
They contain pricey material - silver and, of course, tantalum, so
making them cheaper is impossible. AFAIK they are widely used in
military-grade equipment, where the price is not an issue. Their main
advantages are a longer life (they do not dry out nor leak) and a
bigger temperature range (frost resistance).
About using cheap parts in consumer electronics: At least 80 percent
of failures of certain types of TV sets were caused by dried-out
aluminum caps. The good practice when repairing these sets was: first
check all electrolyte caps by adding a good one in parralel. It was
successful very often.

BR from Ivan
The observations are consistent with the view that electrolytic

capacitor reliability decreases within a short time most other
components have failure modes that take a much longer time to reach the
end of the bathtub.
--
ddwyer

 

[ddwyer]

In article <400fc77e$0$224$fa0fcedb@lovejoy.zen.co.uk>, Fred
<fred@abuse.com> writes

"Jeroen" <Jeroen.Belleman@cern.ch> wrote in message
news:bunvkj$k7e$1@sunnews.cern.ch...
John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.

The high k types vary to +-10% and +20-80% from memory if full temp is

allowed for.
High K doped with piezo material, they can be heard to click if hit with
a square wave.

 

[ddwyer]

In article <bup74o$aot$1@puck.litech.org>, Mike Andrews
<mikea@mikea.ath.cx> writes

Some years ago I wandered into one of the design labs to ask some questions
about a new thingy we were doing.

On a bench was a metal trash can with wires leading to a power supply,
thermometer, and a chart recorder.

[snip]

We got off the floor and looked up to the acoustical ceiling where there
was capacitor pieces and an alligator clip embedded therein.

When the guy running the test said "Maybe we had better rethink this
design", I decided to go back to my lab and come back on a better day.

We continued to use tantalums (aerospace), but there were a lot more
explosions in the lab to make sure they didn't happen on the shipped
product.
Read the data books carefully. There is a formulae relating source

resistance, proof voltage/actual voltage and capacitance.
Note early Plessey button tantalum (very reliable) incorporated liquid
conc nitric? dont blow them up!

--
ddwyer

 

In rec.radio.amateur.homebrew Ken Finney <kenneth.c.finney@boeing.com> wrote:

Silver cased wet slug tantalums DO explode, most contracts that
allow the use of wet slugs require the use of tantalum cased parts.

Some years ago I wandered into one of the design labs to ask some questions
about a new thingy we were doing.

On a bench was a metal trash can with wires leading to a power supply,
thermometer, and a chart recorder.

"What's all this", I ask.

"Getting some real data on stressing tantalums. The trash can is a blast
shield just in case" was the answer.

Just after the guy running the test uttered the words "looks like nothing
bad is going to happen" the cap exploded with the trash can acting as
a megaphone for the bang and director for the shrapnel; everyone around
hit the deck.

We got off the floor and looked up to the acoustical ceiling where there
was capacitor pieces and an alligator clip embedded therein.

When the guy running the test said "Maybe we had better rethink this
design", I decided to go back to my lab and come back on a better day.

We continued to use tantalums (aerospace), but there were a lot more
explosions in the lab to make sure they didn't happen on the shipped
product.

--
Jim Pennino

Remove -spam-sux to reply.

 

[Mike Andrews]

In <bup6n6$9f0$1@mail.specsol.com> (rec.radio.amateur.homebrew), jimp@specsol-spam-sux.com wrote:

Some years ago I wandered into one of the design labs to ask some questions
about a new thingy we were doing.

On a bench was a metal trash can with wires leading to a power supply,
thermometer, and a chart recorder.

[snip]

We got off the floor and looked up to the acoustical ceiling where there
was capacitor pieces and an alligator clip embedded therein.

When the guy running the test said "Maybe we had better rethink this
design", I decided to go back to my lab and come back on a better day.

We continued to use tantalums (aerospace), but there were a lot more
explosions in the lab to make sure they didn't happen on the shipped
product.

As someone who had a big (non-Tantalum) filter cap explode _right_
_next_ to my one-and-only, precious, irreplaceable face, I approve
of this strategy. It sure as blazes beats having a cap in the power
supply drawer imbed itself in the ceiling, missing a cheekbone by
about 1/4", and it also beats having to go through hundreds of power
supplies in the comm center, looking for bulging caps.

We found -- and replaced -- about a thousand. I'm still pretty antsy
about working on anything with filter caps in it, and tend to put a
straight-edge along the can to see if it's bulging. If it _is_, I
just replace it.

--
.... at the end of the conversation, the guy said "Thanks a lot for
reporting this. If you need more details on our anti-spam policies,
just hit 'refresh' on the URL you reported."
-- Willondon Donovan in nanae

 

[ddwyer]

In article <c0tv0013s1ate0ods8264p7gur0o0fecu8@4ax.com>, John Larkin
<jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> writes

Wet-slug tants are expensive (do they still have silver cases?) but
don't blow up like the dry ones. The dry slugs coat the sintered
tantalum (fuel) with MnO2 (oxidizer).
As I mentioned elsewhere some wet slug used conc nitric as the
electroyte (from memory 35 years ago) but very reliable.

--
ddwyer

 

[Tim Wescott]

I've seen more than one problem with high-value ceramics causing problems
during operational vibe tests because of microphonics. In our case it
usually seems to be the vibration causing capacitance change rather than
true piezoelectricity, but it happens in any case. The last one that I
remember we replaced the ceramic caps with back-to-back tantalums, in fact.
Worked like a charm.

"ddwyer" <dd@ddwyer.demon.co.uk> wrote in message
news:z$6M3VAzgCEAFw+P@ddwyer.demon.co.uk...

In article <400fc77e$0$224$fa0fcedb@lovejoy.zen.co.uk>, Fred
fred@abuse.com> writes

"Jeroen" <Jeroen.Belleman@cern.ch> wrote in message
news:bunvkj$k7e$1@sunnews.cern.ch...
John Larkin wrote:

I think multilayer ceramics are pushing 100 uF these days.

Yes, but alas, only with zero volts across them. Capacitance
drops precipitously with DC bias. For a cap with Y5V dielectric,
at half the rated DC voltage, there's only 10% of the initial
capacitance left. Most manufacturers don't tell you.

The high k types vary to +-10% and +20-80% from memory if full temp is
allowed for.
High K doped with piezo material, they can be heard to click if hit with
a square wave.

 

[John Woodgate]

I read in sci.electronics.design that Bill Turner <noway@nohow.com>
wrote (in <7hiv00l0dpa8i70dt2r91tf0b3v9ja5or3@4ax.com&gt about 'Tantalum
caps.', on Thu, 22 Jan 2004:

Consumer electronics are costed down to the lowest possible level. If
they can use something cheaper, they WILL use something cheaper. A TV
set or VCR has had people go over the design hundreds of times with
BOMs and catalogs, checking to see if they can shave a penny here or a
penny there.

_________________________________________________________

Well, maybe. Any manufacturer who has been nailed with thousands of
dollars in warranty costs caused by saving a penny might disagree with
your statement. I've seen it happen.

Epidemic faults were, in my experience, rarely caused by cost-reduction
but either by component manufacturing faults (noisy tantalum caps and
unreliable fuses, for example) or by unrecognized 'gotchas' in the
original circuits (high-Q series resonance in a loudspeaker crossover
filter).
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Woodgate]

I read in sci.electronics.design that OK1SIP <remove_ok1sip@atlas.cz>
wrote (in <5f5159fa.0401212325.d64168f@posting.google.com&gt about
'Tantalum caps.', on Wed, 21 Jan 2004:

tantalum caps seem to be too expensive for consumer-grade equipment.
They contain pricey material - silver and, of course, tantalum,

No. We used quite a lot of tantalum 'bead' caps in consumer audio and TV
until we found the problems they have and we could get aluminium
electrolytics 'with no added salt', so they didn't leak and were much
more reliable. I still have some boards with them fitted.

The problem with Al caps drying out is mainly that people let them get
too hot. They were rated at 75 C or 85 C *max. ambient*, not
'temperature rise'. It's still a problem; we have 'designer' set-top
boxes with no ventilation, and service people put 130 C rated Al caps in
them as replacements; 105 C rated is often not good enough!
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Dr. Anton.T. Squeegee]

In article <bup58t$lf4$1@nntp3.u.washington.edu>, fpm@u.washington.edu
says...

Hi, Frank,

Tektronix was, during that time, strongly discouraging all new designs from
using tantalums. IIRC they had been taken to court over a case in which
a 465 'scope (the original, not the plastic follow-ons) had spontaneously
ignited and had resulted in an expensive fire. Forensics revealed that
a tantalum power-supply bypass cap had started the conflagration. The
drive to reduce tantalum usage was driven primarily by this liability issue,
more than component cost. If you wanted to use a tantalum, you had to
justify its usage to the component/design review committees -- which wasn't
difficult if you had good reasons and your design was solid.

Wow! I didn't know this... Thanks for the neat bit of history.

I will add that most of the tantalums I'm finding in my gear are
localized filters for the power-input traces in 7000-series O-scope
plug-ins.

Everything still works great, though. ;-)


--
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
kyrrin a/t bluefeathertech d-o=t c&o&m
Motorola Radio Programming & Service Available -
http://www.bluefeathertech.com/rf.html
"Quando Omni Flunkus Moritati" (Red Green)

 

[Roy Lewallen]

Frank Miles wrote:

Tektronix was, during that time, strongly discouraging all new designs from
using tantalums. IIRC they had been taken to court over a case in which
a 465 'scope (the original, not the plastic follow-ons) had spontaneously
ignited and had resulted in an expensive fire. Forensics revealed that
a tantalum power-supply bypass cap had started the conflagration. The
drive to reduce tantalum usage was driven primarily by this liability issue,
more than component cost. If you wanted to use a tantalum, you had to
justify its usage to the component/design review committees -- which wasn't
difficult if you had good reasons and your design was solid.

-frank
(ex-Tekie)

I was there at the time, too. Tantalums were essentially verboten unless
the source impedance supplying the tantalum cap was at least 3
ohms/volt. That's because it was found that the short circuit failure
mode was aggravated by high inrush current, so the source current had to
be limited. One of the chief reasons we had been using tantalums in the
first place is that they have very good bypass characteristics up to
quite high frequencies -- so a single capacitor could handle a very wide
range. When the source impedance was high, the capacitor didn't need to
be so good in the first place, and of course adding a physical resistor
in series with a supply bypass pretty much defeats the whole purpose.
Consequently, the 3 ohms/volt rule pretty much eliminated tantalums as a
viable choice for most applications. Fortunately, it was at just about
the same time that very big improvements were made in aluminum capacitor
technology. As the aluminums shrunk in size, they became much better at
bypassing higher frequencies. So they took over from tantalums pretty
rapidly. There was a glitch for a while, though -- boards were being
cleaned with Freon at the time, and it was discovered that Freon could
migrate past the seals on some or most aluminum capacitors and corrode
the aluminum, leading to poor reliability. The solution adoped by some
manufacturers was to add a rubber seal at the lead end of the capacitor.
That increased the length of the leads between the outside of the
capacitor and the inner body, increasing the lead inductance and
decreasing the capacitor's high frequency bypass capability. . . but
that's just another example of the day-to-day problems an engineer faces
and has to overcome.

Incidentally, I got a Tek 1502 TDR on eBay not long ago. It had a
shorted tanalum power supply bypass capacitor.

A couple of other anecdotes -- A time base plugin I designed had gotten
through the entire extensive pre-production test phases, accelerated
life tests, etc., and was in pilot production. I walked past the
production line technician's bench every day, and began noticing several
tantalum capacitors of the same type in the replaced-component box. They
had come from a sweep circuit I had essentially copied from an
instrument which had been in production for some time. Puzzled, I
analyzed the circuit carefully, and discovered that at an extreme
setting of one control, the tantalum cap could have a very small reverse
voltage applied. I modified the circuit to eliminate the possibility of
any reverse voltage of any level, and the capacitors quit failing.
Servicing data from the instrument I had copied the circuit from showed
noticeably reduced reliability of the capacitor, also. The lesson
learned is that tantalums won't tolerate _any_ reverse voltage. If they
don't fail immediately, a disproportionate number will fail eventually.

The other anecdote involves a QRP rig. As a crude reverse-voltage
protection, I had reverse-connected a 3-watt diode (actually, a 36 volt
zener I had lots of) across the power supply terminals. My battery
supply normally had an-line fuse which would blow. Just before Field Day
one year, the fuse holder broke and I didn't have a spare in the junk
box. I'd never blown a fuse in 20 years of Field Days, so went without.
The battery was a 12 volt, 5 Ah sealed lead acid unit, capable of a few
hundred amps if shorted. As I'm sure you've guessed, that was to be The
Year of the Reverse Connected Supply. The wires to the battery
immediately melted out of their insulation, burning some holes in the
tent floor. I managed to disconnect the battery without getting burned
and before a real fire started, and checked the damage. The rig's
(recently installed) power switch was fortunately off, so the innards
didn't get any reverse voltage. The diode had gotten so hot that the
plastic case had fractured and probably burned -- it was gone. The
diode's solder joints had melted, and the two separated diode leads were
dangling. But there was still a dead short across the terminals -- a
small 6.8 uF dipped tantalum capacitor was also across the terminals,
and it had become such a good short that it hadn't gotten hot enough to
explode. (The power supply wires were something like #24 or #26, so
they'd limited the current.) My guess is that it went short just as soon
as the diode opened, and made a better quality short than the diode had.
The fuse is now back in place (along with new diode and capacitor), so
of course I haven't reverse connected the supply since.

Roy Lewallen, W7EL

 

[Lewin A.R.W. Edwards]

Consumer electronics are costed down to the lowest possible level. If
they can use something cheaper, they WILL use something cheaper. A TV

Well, maybe. Any manufacturer who has been nailed with thousands of
dollars in warranty costs caused by saving a penny might disagree with
your statement. I've seen it happen.

Caused by bad engineering (or purchasing), I would say.

"Costing down" does not mean "making inappropriate component
substitutions", and I wasn't suggesting or advocating such a policy.
It means, quite simply, going over the circuit and seeing where a
cheaper design or a cheaper, _compatible_ substitute can be used. If
the device has a 12 month warranty, and it dies after that period
expires, then nobody really cares which component was the first to
fail. Especially in disposable consumer electronics!

 

[Walter Harley]

"Roy Lewallen" <w7el@eznec.com> wrote in message
news:1010hb9gigfli91@corp.supernews.com...

analyzed the circuit carefully, and discovered that at an extreme
setting of one control, the tantalum cap could have a very small reverse
voltage applied. I modified the circuit to eliminate the possibility of
any reverse voltage of any level, and the capacitors quit failing.

How much voltage? We talking tens, hundreds, or thousands of mV?

 

[Roy Lewallen]

Walter Harley wrote:

"Roy Lewallen" <w7el@eznec.com> wrote in message
news:1010hb9gigfli91@corp.supernews.com...

analyzed the circuit carefully, and discovered that at an extreme
setting of one control, the tantalum cap could have a very small reverse
voltage applied. I modified the circuit to eliminate the possibility of
any reverse voltage of any level, and the capacitors quit failing.


How much voltage? We talking tens, hundreds, or thousands of mV?

As I recall, it was a couple of tenths of a volt. The capacitor was
probably a 12 or 25 volt unit.

A quick scan of the web shows that some manufacturers claim their
tantalum capacitors will withstand something like 10% of rated voltage
(not to exceed 1 volt) at 25 degrees C, and 3 - 5% of rated voltage (not
to exceed 0.5 volt) at 85 degrees C, with a time limit on application of
reverse voltage. Because of my experience, though, I'd consider it to be
bad design practice to allow any reverse voltage at all until I saw some
reliability figures for capacitors used under those conditions. The
problem is that it doesn't cause immediate failure, or even assured
failure -- it just increases the probability of failure. Some
applications can tolerate the increased failure rate, and some can't. At
Tek, a great deal of importance was placed on reliability.

Roy Lewallen, W7EL

 

[Charles Edmondson]

jimp@specsol-spam-sux.com wrote:

In rec.radio.amateur.homebrew Ken Finney <kenneth.c.finney@boeing.com> wrote:




Silver cased wet slug tantalums DO explode, most contracts that
allow the use of wet slugs require the use of tantalum cased parts.



Some years ago I wandered into one of the design labs to ask some questions
about a new thingy we were doing.

On a bench was a metal trash can with wires leading to a power supply,
thermometer, and a chart recorder.

"What's all this", I ask.

"Getting some real data on stressing tantalums. The trash can is a blast
shield just in case" was the answer.

Just after the guy running the test uttered the words "looks like nothing
bad is going to happen" the cap exploded with the trash can acting as
a megaphone for the bang and director for the shrapnel; everyone around
hit the deck.

We got off the floor and looked up to the acoustical ceiling where there
was capacitor pieces and an alligator clip embedded therein.

When the guy running the test said "Maybe we had better rethink this
design", I decided to go back to my lab and come back on a better day.

We continued to use tantalums (aerospace), but there were a lot more
explosions in the lab to make sure they didn't happen on the shipped
product.


Few years ago, my boss came in, laid a printed schematic on my desk, and

said "Put this in PSpice, so we can demo it to a customer. I said OK,
and started entering the design. He comes in a couple of hours later,
and wants to know if it is finished! I go, SaWha? He now tells me that
he is getting on a plane in a few hours, and has a meeting with the
customer in the morning! So I get to it, end up emailing it to him the
next morning, as there were some digital parts not in the standard
libraries, had several components that I had to create, etc. There are
still major bugs in the simulation, etc. That afternoon, he calls, and
says that they were mad because they didn't see what they were looking
for in the simulation. I ask, What were they looking for? And he tells
me, this cap in the power supply keeps exploding! I then realize he is
talking about the tantalum! Since I had just seen a thread like this
one, I knew about tantalums, so I told him that there was no way we were
going to create a special model for PSpice for tantalum caps! Most
designers just knew not to use them as power supply filters!

Got a bad review from him that year. I now know that, when you get an
assignment, ask LOTS of questions, to the actual customer whenever
possible!

Charlie
Edmondson Engineering
Unique Solutions to Unusual Problems

 

[Tom Bruhns]

"Henry Kolesnik" <wd5jfr@oklahoma.net> wrote in message news:<100u2kvskpbroc8@corp.supernews.com>...

Over the last few years I've acquired quite a few consumer electronincs pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a
tantalum to repair some test equipment I was going to salvage a tantalum. I
couldn't find one anywhere, so I assume they're too expensive or too
unrelaible for high end consumer electronics. A couple of the boards were
from my personal stuff purchased new. One example is a MGA Mitsubishi rear
projection TV that operated flawlessly for nearly 20 years of daily use.
Most of my test equipment comes from hamfests and is surplus after becoming
obsolete and non-operative in less than 20 years. That leads me to wonder
what the real story is behind tantalum capacitors. What do the experts have
to say?
tnx
hank wd5jfr

Didn't see anyone else mention that aluminum electrolytics don't work
well when cold, but tantalums keep working fine.

Your test equipment probably became "obsolete" because the things
being tested were newer and more sophisticated than the equipment was
designed for, and therefore it was no longer needed. Technology moves
along rather swiftly these days. If all analog TV signals were
discontinued with only digital available, your old rear projection TV
would also be obsolete. Test equipment is commonly much more
sophisticated than consumer...drifts that are practically unnoticable
in consumer electronics would be intolerable in test equipment. But
even so, I have plenty of test equipment that's 20+ years old that
still works fine. I've had to repair (or toss) a higher percentage of
my consumer electronics than of my test equipment, for sure.
"Discman" type CD players seem to have an especially short life, but
I've had tape recorders, TVs and at least one stereo amplifier fail as
well.

Cheers,
Tom

 

[John Larkin]

On Thu, 22 Jan 2004 18:12:20 GMT, "Ken Finney"
<kenneth.c.finney@boeing.com> wrote:

"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:c0tv0013s1ate0ods8264p7gur0o0fecu8@4ax.com...
On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"
tim@wescottnospamdesign.com> wrote:

I wouldn't assume that just because your test equipment comes to you
broken
is a result of tantalum caps -- perhaps your sample is skewed by buying
at
hamfests instead of burgling active technology companies? Maybe if you
only
acquired your home entertainment equipment from dumpsters you'd conclude
that aluminum electrolytics are bad?

I recently escaped from a company that does aero (but not space) systems.
They get mounted on aircraft and are expected to survive being shipped in
an
unpressurized cargo hold at 50000 feet. At that altitude a wet aluminum
electrolytic will dry out, but a tantalum will be fine. There are even
wet-slug tantalums for high-altitude applications that will not dry out
at
these altitudes.


Wet-slug tants are expensive (do they still have silver cases?) but
don't blow up like the dry ones. The dry slugs coat the sintered
tantalum (fuel) with MnO2 (oxidizer).


snip

Silver cased wet slug tantalums DO explode, most contracts that
allow the use of wet slugs require the use of tantalum cased parts.

Sure, any cap will explode if you dump enough energy into it. The
difference is that the dry Ta:MnO2 guys only need a tiny bit of energy
to ignite, then chemically explode on their own. Just a high dV/dT
will set one off.

John

 

[Henry Kolesnik]

I've started a new thread with a partial respnse to your comments Subject:
Tantalums and test eqpt
73
hank wd5jfr
"Tom Bruhns" <k7itm@aol.com> wrote in message
news:3200347.0401221736.13a164b@posting.google.com...

"Henry Kolesnik" <wd5jfr@oklahoma.net> wrote in message
news:<100u2kvskpbroc8@corp.supernews.com>...
Over the last few years I've acquired quite a few consumer electronincs
pcbs
including TVs, VCRs, stereos, etc, so when I discovered that I needed a
tantalum to repair some test equipment I was going to salvage a
tantalum. I
couldn't find one anywhere, so I assume they're too expensive or too
unrelaible for high end consumer electronics. A couple of the boards
were
from my personal stuff purchased new. One example is a MGA Mitsubishi
rear
projection TV that operated flawlessly for nearly 20 years of daily use.
Most of my test equipment comes from hamfests and is surplus after
becoming
obsolete and non-operative in less than 20 years. That leads me to
wonder
what the real story is behind tantalum capacitors. What do the experts
have
to say?
tnx
hank wd5jfr

Didn't see anyone else mention that aluminum electrolytics don't work
well when cold, but tantalums keep working fine.

Your test equipment probably became "obsolete" because the things
being tested were newer and more sophisticated than the equipment was
designed for, and therefore it was no longer needed. Technology moves
along rather swiftly these days. If all analog TV signals were
discontinued with only digital available, your old rear projection TV
would also be obsolete. Test equipment is commonly much more
sophisticated than consumer...drifts that are practically unnoticable
in consumer electronics would be intolerable in test equipment. But
even so, I have plenty of test equipment that's 20+ years old that
still works fine. I've had to repair (or toss) a higher percentage of
my consumer electronics than of my test equipment, for sure.
"Discman" type CD players seem to have an especially short life, but
I've had tape recorders, TVs and at least one stereo amplifier fail as
well.

Cheers,
Tom

 

[Asimov]

"Roy Lewallen" bravely wrote to "All" (22 Jan 04 13:49:22)
--- on the heady topic of "Re: Tantalum caps."

RL> From: Roy Lewallen <w7el@eznec.com>
RL> Just before
RL> Field Day one year, the fuse holder broke and I didn't have a spare in
RL> the junk box. I'd never blown a fuse in 20 years of Field Days, so
RL> went without. The battery was a 12 volt, 5 Ah sealed lead acid unit,
RL> capable of a few hundred amps if shorted. As I'm sure you've guessed,
RL> that was to be The Year of the Reverse Connected Supply. The wires to
RL> the battery immediately melted out of their insulation, burning some
RL> holes in the tent floor. I managed to disconnect the battery without
RL> getting burned and before a real fire started, and checked the damage.
RL> The rig's (recently installed) power switch was fortunately off, so
RL> the innards didn't get any reverse voltage. The diode had gotten so
RL> hot that the plastic case had fractured and probably burned -- it was
RL> gone. The diode's solder joints had melted, and the two separated
RL> diode leads were dangling. But there was still a dead short across the
RL> terminals -- a small 6.8 uF dipped tantalum capacitor was also across
RL> the terminals, and it had become such a good short that it hadn't
RL> gotten hot enough to explode. (The power supply wires were something
RL> like #24 or #26, so they'd limited the current.) My guess is that it
RL> went short just as soon as the diode opened, and made a better quality
RL> short than the diode had. The fuse is now back in place (along with
RL> new diode and capacitor), so of course I haven't reverse connected the
RL> supply since.
RL> Roy Lewallen, W7EL

You should have added a cheap automotive relay with a series diode
powering the coil, and maybe thrown in a red led idiot light to
indicate the reverse polarity. ;-)

.... Dunno if we'll get that past the CSA und UL 'owever.