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!

"Roy Lewallen" wrote in message
...
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?

Walter Harley wrote:
"Roy Lewallen" wrote in message
...

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

wrote:

In rec.radio.amateur.homebrew Ken Finney 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! 8-)

Charlie
Edmondson Engineering
Unique Solutions to Unusual Problems

"Henry Kolesnik" wrote in message ...
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

On Thu, 22 Jan 2004 18:12:20 GMT, "Ken Finney"
wrote:


"John Larkin" wrote in
message ...
On Wed, 21 Jan 2004 22:21:31 -0800, "Tim Wescott"
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

I've started a new thread with a partial respnse to your comments Subject:
Tantalums and test eqpt
73
hank wd5jfr
"Tom Bruhns" wrote in message
...
"Henry Kolesnik" wrote in message
...
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

In sci.electronics.design Tom Bruhns wrote:
"Henry Kolesnik" wrote in message ...
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?

snip
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

To take this as an example, set-top boxes to act as a TV tuner will be
available for a long while after analog switchoff.

Don't mean to beat a dead topic to a second death, but in case you wanted to
know NASA uses tantalums extensively as replacements for electrolytics
on-orbit (on station & shuttle). I don't can't recite the reasoning
verbatim, but it is an M&P (materials and processes) issue, having to do
with operating at low pressures and also the dangers of electrolytics
entering various failure modes due to overheating in space (no
bouyancy-driven convection). Tantalums tend not to fail catastrophically
(pop or explode) when thermally stressed.

Jason Dugas
KB5URQ
NASA-JSC

"Henry Kolesnik" wrote in message
...
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

Frank Miles wrote:

In article ,
Dr. Anton.T. Squeegee wrote:
In article ,
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 whe

(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.

Ah ha! I have a 465 (w/DM44) that I purchased in 1978 for personal use
(no commercial abuse). Shortly after the warranty expired, it would not
power up.
I traced the problem to a shorted tantalum filter cap on the +15 volt
line.
But of course, it wasn't in the power supply, but rather on one of the
boards.
Pain to get to, IIRC.

BTW, I did not get option 5 (TV sync separator). I wonder if it is
feasable to
install it myself? Documentation is listed as 465 option 5 supplement
070-2191-00.
Anyone have this info?

--
Jerry wa2rkn no email @ present