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

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

Jerry Koniecki wrote:

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.

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.

I can imagine. Tantalum caps are a real pain in the ass. If you
reverse the polarity, they burn right through the PCB after a few
months! We got a board in for repair last week with that problem.
Luckily, everything on the board (yes, even the stickers with the
serial numbers) is self extinguising.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

Jerry Koniecki wrote in message ...
Frank Miles wrote:

..snippety...

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?


Yes, you can install it youself. The OPt.5 is a small extra board,
basically a video clamp circuit. There is a small ek special IC on the
board, but when you analyze the circuit you will recognize that a quad
op-amp of gain-BW 5 MHz will work well.
At least at mine it does so.

Scopes with option 5 have a differnt front panel layout. So, you might
get in trouble to realize this with your non-opt5 scope.
But basically: Yes, it can be field installed.


hth,
Andreas

Jerry Koniecki wrote:

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.

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.

I can imagine. Tantalum caps are a real pain in the ass. If you
reverse the polarity, they burn right through the PCB after a few
months! We got a board in for repair last week with that problem.
Luckily, everything on the board (yes, even the stickers with the
serial numbers) is self extinguising.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

Jerry Koniecki wrote in message ...
Frank Miles wrote:

..snippety...

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?


Yes, you can install it youself. The OPt.5 is a small extra board,
basically a video clamp circuit. There is a small ek special IC on the
board, but when you analyze the circuit you will recognize that a quad
op-amp of gain-BW 5 MHz will work well.
At least at mine it does so.

Scopes with option 5 have a differnt front panel layout. So, you might
get in trouble to realize this with your non-opt5 scope.
But basically: Yes, it can be field installed.


hth,
Andreas

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

"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

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.