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I am guessing that this subject has been hashed over a number of times but as I am fairly new here i will ask away.

I see on the different boards from the scopes I now have some from same unit and others same board different scopes that there is a vast array of colors of tants used. So my question are the solid blue ones better than the multi color ones or just a new better one.
Also what are the differences between the solid blue, solid orange and ones that are brown, green, blue?
Looking at Digikey and Mouser which are the best manufacturer of the new ones? There is a big difference in price.
On a couple of the main boards there are some leaking silver tants so best type replacement to use there or just replace with a appropriately adjusted electrolytic?
One board has a burned up tant and scorched board and other components will have to test them. I am thinking to replace all the multi colored ones with newer from one of the suppliers especially the wet axial ones they haven't leaked enough to damage the board but just barely. How does one dispose of the bad wet ones/

Jim

The only type you have to be concerned about are bead tantalum capacitors used for local power supply
rail decoupling. Colour is unimportant.

They will be 6V rating on 5V rails and 16V rating on 15V rails. And bewilderingly 50V rating on 50V
rails. They randomly fail as a dead short. Replace them with low ESR aluminium electrolytic with
three times the capacitance. That is exactly what Tek did in later serial numbers.

Anywhere else - as coupling capacitors between stages for example - are generally just fine.

I have never personally seen a wet tantalum leak. Which is just as well because replacements cost a
king's ransom.

Craig

On Wed, 18 Jul 2018, Craig Sawyers wrote:

The only type you have to be concerned about are bead tantalum capacitors
used for local power supply rail decoupling. Colour is unimportant.

They will be 6V rating on 5V rails and 16V rating on 15V rails. And
bewilderingly 50V rating on 50V rails. They randomly fail as a dead short.
Replace them with low ESR aluminium electrolytic with three times the
capacitance. That is exactly what Tek did in later serial numbers.

Better yet replace them with higher voltage rated ones if they are
available. 20V tantalum lasts forever on 5V rail as well as 35V one on 15V.

Anywhere else - as coupling capacitors between stages for example - are
generally just fine.

I have never personally seen a wet tantalum leak. Which is just as well
because replacements cost a king's ransom.

I can send you a handful :) They _ALWAYS_ leak sooner or later because of
their very chemistry. They are filled with sulfuric acid and although silver
sulfate has very low solubility it is still not zero so sooner or later that
nice silver can turns to sieve. And the fact they are almost always used at
their rated voltage or even above also doesn't make them last longer...

I have dozens of those leaked in 492BP/494AP SAs that I refurbish on a
regular basis. The same is true for those HP 835xx microwave plugins that I
revived quite a few -- I have never seen a single such plugin that didn't
have at least one leaked wet tantalum. The most spectacular was one 83572A
plugin where sulfuric acid from one big wet tantalum ate off it leads
completely, spilled on the motherboard and ate a hole through the entire
motherboard PCB, through all of its copper and fiberglass layers.

Craig

Subject: [TekScopes] tants new vs old

I am guessing that this subject has been hashed over a number of times but as I am fairly new here i
will ask away.

---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*

On 18/07/18 06:46, Craig Sawyers wrote:

I have never personally seen a wet tantalum leak. Which is just as well because replacements cost a
king's ransom.

I have had axial tantalum capacitors leak and destroy nearby PCB traces, specifically
C6246 and C6341 in a Tek 1502 TDR.

The only place I've ever seen a wet tantalum leak is in the 184 TMG; fortunately, corrosion was limited to the capacitor leads themselves.? There must be environmental factors at work, because some people see a lot of wet Ta failures.? It's probably high ambient temperatures.?
-Dave

From: Craig Sawyers <c.sawyers@...>
To: [email protected]
Sent: Tuesday, July 17, 2018 10:47 PM
Subject: Re: [TekScopes] tants new vs old

The only type you have to be concerned about are bead tantalum capacitors used for local power supply
rail decoupling. Colour is unimportant.

They will be 6V rating on 5V rails and 16V rating on 15V rails. And bewilderingly 50V rating on 50V
rails. They randomly fail as a dead short. Replace? them with low ESR aluminium electrolytic with
three times the capacitance. That is exactly what Tek did in later serial numbers.

Anywhere else - as coupling capacitors between stages for example - are generally just fine.

I have never personally seen a wet tantalum leak. Which is just as well because replacements cost a
king's ransom.

Craig

Subject: [TekScopes] tants new vs old

I am guessing that this subject has been hashed over a number of times but as I am fairly new here i
will ask away.

Hi Craig,

You would think that should be the case but as I commented on a recent thread, I've got a whole bunch of Tek 7000 series stuff working over the last couple of years, most recently the 7912AD and I guess I've replaced well over a dozen dead-short Tants in that time.

All bar one was blue, the other was 'brown with stripes' none have been yellow or orange. Yet, I would say that an (unscientifically derived) statistic is there are more yellow & orange Tants present in the equipment. Now, I've not looked to see if, for instance yellow/orange are always 5V and so on - just my observation - along with the comment I have worked on as much HP gear and have never had to replace a single Tant in that but don't even know if they used them though!

I assume the colour may be an indicator of manufacturer (the yellow is very 'AVX'?) I wonder if anyone else has noticed a colour bias in the failure rate?

...I now await a puff of (yellow/orange) smoke from the bench......

Adrian

The only place I've ever seen a wet tantalum leak is in the 184 TMG; fortunately, corrosion was
limited
to the capacitor leads themselves. There must be environmental factors at work, because some
people see a lot of wet Ta failures. It's probably high ambient temperatures. -Dave

The only thing that can degrade a rubber-sealed wet tantalum, and also (particularly) axial
electrolytics, is the flux cleaning regime. As an example I bought a NOS P6046 differential probe, and
needed to change the power supply to 240V from 110V. Good job - the axial electrolytics were leaking
out of the rubber end seal and was chomping the circuit board traces. That was almost certainly a
result of defluxing solvent that was used, which penetrated the end seals causing long term
degradation. More affordable wet tantalum (which are still punishingly expensive) have/had rubber
seals which even when perfect can allow slow water loss, particularly over 100C.

Wet tantalum is used extensively in military and space applications, and is known for its long-term
reliability. Although an older paper this sets out the inherent reliability
downloads.hindawi.com/journals/apec/1976/123103.pdf .

Typical cost for a regular grade AVX wet tantalum, 400uF/100V is UKP176.

Also, current information from Vishay, particularly "Product which has been built and test supported
to 10 000 hours (per MIL Specification) has seen useable life well beyond twenty years. Some of the
tantalum products were the space probes launched in the 1970's which are still going."


And for glass hermetic sealed versions (which
resists water loss).

As a result, these hermetically sealed mil spec ones are seriously not cheap. But if you need long
life, and tiny leakage currents, and extended life, wet tant is the way to go.

Craig

Better yet replace them with higher voltage rated ones if they are available. 20V tantalum lasts

forever

on 5V rail as well as 35V one on 15V.

Well, yes. All I'm saying is that I have identical plugins (such as 7A26) in which at some point Tek
went from tant bead to aluminium electrolytic. So substitution is tried and tested.

And low ESR is not as good for tantalum beads as compared with modern low ESR aluminium
electrolytics designed for switched mode supplies. As an example an AVX 47uF 35V tantalum bead has
an ESR at 100kHz of 0.8 ohms. A Panasonic FR of the same capacitance, but 25V rated has an ESR of
0.3 ohms at 100kHz.

I can send you a handful :) They _ALWAYS_ leak sooner or later because of their very chemistry.

They

are filled with sulfuric acid and although silver sulfate has very low solubility it is still not

zero so sooner

or later that nice silver can turns to sieve. And the fact they are almost always used at their

rated

voltage or even above also doesn't make them last longer...

Operating any capacitor at or above its rated voltage is a short term recipe for capacitor death
regardless of chemistry. Even with wet tant, the current recommendation is that for long life the
rated voltage should be at least 1.6 times the operating voltage.

I have dozens of those leaked in 492BP/494AP SAs that I refurbish on a regular basis. The same is

true

for those HP 835xx microwave plugins that I revived quite a few -- I have never seen a single such
plugin that didn't have at least one leaked wet tantalum. The most spectacular was one 83572A

plugin

where sulfuric acid from one big wet tantalum ate off it leads completely, spilled on the

motherboard

and ate a hole through the entire motherboard PCB, through all of its copper and fiberglass

layers.

That is impressive! Were these rubber sealed versions?

Craig

I have had axial tantalum capacitors leak and destroy nearby PCB traces, specifically
C6246 and C6341 in a Tek 1502 TDR.

Interesting - must check mine. Wonder why they used them only on the +25V rail, which is only used on
the high voltage board, to feed the switching transistors on the primary of the HV transformer, but
regular electrolytics on the other rails? Noted that these wet tants are 30V parts on a 25V rail
(rated = 1.2 rail voltage), so is somewhat close to the wire.

Craig

On 18/07/18 09:29, Craig Sawyers wrote:

I have had axial tantalum capacitors leak and destroy nearby PCB traces, specifically
C6246 and C6341 in a Tek 1502 TDR.

Interesting - must check mine. Wonder why they used them only on the +25V rail, which is only used on
the high voltage board, to feed the switching transistors on the primary of the HV transformer, but
regular electrolytics on the other rails? Noted that these wet tants are 30V parts on a 25V rail
(rated = 1.2 rail voltage), so is somewhat close to the wire.

It has only happened in 20% of my 1502s. I seem to have a
fetish for the damn things :)

ISTR the 25V rails are not low current, which might increase
the stress.

On Wed, 18 Jul 2018, Craig Sawyers wrote:

Better yet replace them with higher voltage rated ones if they are available. 20V tantalum lasts

forever

on 5V rail as well as 35V one on 15V.

Well, yes. All I'm saying is that I have identical plugins (such as 7A26)
in which at some point Tek went from tant bead to aluminium electrolytic.
So substitution is tried and tested.

That is fine where it is possible. Alas there are places where it is
difficult to make such a replacement. Just for example -- there are some
high capacitance (something like 1,000uF 25V) wet tantalums in 494AP inside
RF enclosures that were used because of much higher capacitance per volume
and it is almost impossible to find an aluminum capacitor that would've fit
into those enclosures even with same capacitance. Trying to find something
of the same size with bigger capacitance to properly replace a tantalum
doesn't make the task any easier :)

And low ESR is not as good for tantalum beads as compared with modern low
ESR aluminium electrolytics designed for switched mode supplies. As an
example an AVX 47uF 35V tantalum bead has an ESR at 100kHz of 0.8 ohms. A
Panasonic FR of the same capacitance, but 25V rated has an ESR of 0.3 ohms
at 100kHz.

There are low-ESR tantalums these days that are even better :) There are
also other considerations like limited life of those aluminum/polymer
capacitors, much higher leakage currents, bigger size etc. For power
supplies those are OK but they won't fit the bill where some unique tantalum
features are needed. And one should not forget that all aluminum capacitors,
polymer or not, are _WOUND_ ones unlike tantalums so they have much higher
inductance.

Properly chosen tantalum essentially lasts forever unlike aluminum which is
also a factor.

I can send you a handful :) They _ALWAYS_ leak sooner or later because of their very chemistry.

They

are filled with sulfuric acid and although silver sulfate has very low solubility it is still not

zero so sooner

or later that nice silver can turns to sieve. And the fact they are almost always used at their

rated

voltage or even above also doesn't make them last longer...

Operating any capacitor at or above its rated voltage is a short term recipe for capacitor death
regardless of chemistry. Even with wet tant, the current recommendation is that for long life the
rated voltage should be at least 1.6 times the operating voltage.

I have dozens of those leaked in 492BP/494AP SAs that I refurbish on a regular basis. The same is

true

for those HP 835xx microwave plugins that I revived quite a few -- I have never seen a single such
plugin that didn't have at least one leaked wet tantalum. The most spectacular was one 83572A

plugin

where sulfuric acid from one big wet tantalum ate off it leads completely, spilled on the

motherboard

and ate a hole through the entire motherboard PCB, through all of its copper and fiberglass

layers.

That is impressive! Were these rubber sealed versions?

They were teflon sealed. But that doesn't matter because vast majority of
them didn't leak through the seal. They had their silver cans eaten through.

The very first sign of imminent failure is intense blackening around
NEGATIVE lead and then case color change under the thermosetting sleeve.
Sulfuric acid etches the can and finds its way out through microscopic (not
even "pinhole") holes first. Capacitor at this stage is still mechanically
sound and most of that miniscule quantity either dries out around hegative
lead or gets trapped inside the plastic sleeve thus changing the case color.
The capacitor is still within its specs at this point but its case is
already seriously weakened and mechanical failure is just around the corner.
And when it finally happens the capacitor simply breaks into pieces and all
sulfuric acid it contained gushes out making a big puddle that eats whatever
it gets in contact with.

The above scenario applies to properly used wet tantalums. Those cheaper
rubber-sealed ones in e.g. 7000-series plugins usually have different
failures mechanism -- they were used at their full rated voltage and even
above and had significant ripple currents running through them so they
overheated and boiling sulfuric acid found its way out through positive
terminal seal way before it got a chance to eat through the silver can.

---
*
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
*

Just wanted to get a little clarity here and also do an update. Went through a number of the scopes I have now and have found three of them where the wet tant has already been replaced with aluminum electrolytics same one that is leaking on the 466 board I am working on. On one of them it was replaced with a 1000uf 10v and on another a 1000uf 35v was used they replaced a 1000uf 10v wet tant they are both larger but fit in place. There is no way to fit a three times capacitance increase in place for that one found a 3300uf 16v that is closest to it at 3 times. There is a very small wet one used on the 464/466 that is 3.6uf 125v that is leaking on the one board I can get a 10uf 160v to replace it think it will fit but would using a solid bulb type of tant same uf but higher voltage be a better choice?
Made a list of wet tants used and what aluminum lytics I could get to replace with and most are close for fitting there are three leakers on this board and one iffy.

Jim