I have recently acquired a 3458A which incorporates a Schaffner FN9223-3-06 mains filter. The 3458A has a build date of approx 2005 and the Schaffner filter has a date code of 0432.

I am wondering if these later Schaffner filters have the same dramatic failure mode exhibited by their earlier models and whether it should be replaced. I am reluctant to replace it if it is not necessary due to it being riveted into the chassis.

开云体育

As far as I know there is not a problem. We've fitted hundreds of assorted types of Schaffner IEC input filters to equipment since the mid 1990s and as far as I know without any failure. I suppose there may have been failures but our customers may just not have mentioned it to us? (Unlikely!)

It is true that most of those will have been living in 220/240VAC land their whole lives whereas the only HP fitted one I've had fail went within a day or so of crossing the Atlantic and seeing 240V for the first time.

Any 'stand alone' yellow Rifa caps you find serving as input filters should be changed with extreme prejudice on sight however!?

On 2022-09-06, at 10:58, Adrian Nicol <Adrian@...> wrote:

Any 'stand alone' yellow Rifa caps you find serving as input filters should be changed with extreme prejudice on sight however!

Yes. The point about Schaffner filters is that X caps of this type (reportedly from WIMA, not RIFA) were use in their line filters up to some point, which (together with the fact that they make a somewhat sealed enclosure) is the reason they explode.

The question really is when Schaffner stopped using the “clear epoxy blob” type of X cap and switched to caps that didn’t have that fatal flaw.

Your data seems to suggest mid-1990s or earlier.

Can we get more precise?
Maybe obtain a statement from the horse’s mouth?
(Somebody in this mailing list must have worked for Schaffner…)

Grü?e, Carsten

If you are in the USA, you will probably never witness
a Schaffner filter fail. If you are in 220-240V land, you
may not be so lucky.

When the filters fail, the worst that happens is they release
a little foul smoke, and sometimes a little tar. Both problems
are pretty easy to clean up... if they happen.

Being in the US, my policy is to leave them alone, and to
fix any that fail, when they fail. If I were in 220-240V land,
I would replace them on sight. The rivets are a simple problem.
Center punch them, drill them out, and use a fresh pop rivet
when you replace the filter.

-Chuck Harris


On Tue, 06 Sep 2022 01:30:40 -0700 "Stephen Bell"
<s.r.bell@...> wrote:

I have recently acquired a 3458A which incorporates a Schaffner
FN9223-3-06 mains filter. The 3458A has a build date of approx 2005
and the Schaffner filter has a date code of 0432.

I am wondering if these later Schaffner filters have the same
dramatic failure mode exhibited by their earlier models and whether
it should be replaced. I am reluctant to replace it if it is not
necessary due to it being riveted into the chassis.

On Tue, Sep 6, 2022 at 2:14 PM Chuck Harris <cfharris@...> wrote:

If you are in the USA, you will probably never witness
a Schaffner filter fail. If you are in 220-240V land, you
may not be so lucky.

When the filters fail, the worst that happens is they release
a little foul smoke, and sometimes a little tar. Both problems
are pretty easy to clean up... if they happen.

Being in the US, my policy is to leave them alone, and to
fix any that fail, when they fail. If I were in 220-240V land,

I definitely live in 240V land (even more when the PV plant is active).
Many schaffner filters died or were found dead when I acquired various
test gears.
However, I've not replaced them "on sight", I still have a few
instruments (Solartron, Data I/O)
with the original filters and I don't plan to mess with them unless
they release the magic and stinky
smoke first.

Frank IZ8DWF

Yeah, I've had them go bang on other instruments and it makes a mess. You might want to do it at the same time as the electrolytics and also socket and renew the battery-backed sram if it's not already. Here's my parts list:



The key thing to avoid an unnecessary recal, of course, is to extract the calram contents promptly. There are loads of utilities around to do that over gpib.

There's lots of discussion on this and related subjects on the eevblog metrology forum.

Alan

I haven't replaced the schaffner filter on my two 3458A's. Keysight don't change them automatically if they repair a unit, so I guess they? are not expecting them to fail suddenly.

If you do replace the shaffner, also consider C15/16 on the outguard power supply board which are 2200pF 250VAC rated - and on mine look like rifa's.

On 2022-09-06, at 18:27, Keith <keith@...> wrote:

I haven't replaced the schaffner filter on my two 3458A's. Keysight don't change them automatically if they repair a unit, so I guess they are not expecting them to fail suddenly.

I don’t know off-hand how similar the 3457A ones are, but these do fail, and need to be replaced on sight.

(And I do hate those rivets — drilling them out is not what I want to do, given the danger of metal shavings making it into the instrument.)

Grü?e, Carsten

Yep, had a Schaffner, filter, fuse, switch combo on an HP 4951C released both magic smoke and tar 10 min after powering up this ebay purchase out of the US, on 240V in the land down under. Don't know which was worst, breathing the acrid smoke or cleaning the tar off of some of the components on the main PCB.

Regards,
Peter

Funny you mention the clear encapsulation.

So I have some RIFA's I ordered and received from digikey in 2018. I
saved them for a project in the original antistatic bag in a cardboard
box in the unlite closet. So no UV exposure. I keep my office
relatively temperature controlled because of the test equipment there.
Imagine my fascination when I opened the box last year and found that
they had cracked. Keep in mind this isn't a large sample size it's
just 3 or 4 capacitors but to me it says a lot. I don't believe the
failure mode for the RIFA's is heating and drying out or whatever.
IMHO the encapsulation failure is the root cause. I suspect the
acrylic has a lot of internal stress from a rapid curing process used
by RIFA.

-Evan Foss

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I should have mentioned in my original post that I live in 230V land and I have already directly witnessed quite a number of Schaffner filters and RIFA capacitors fail with the release of a lot of the magic smoke along with a revolting stench. All the failures I have witnessed so far have been the earlier FN323 and FN326 series with date codes ranging through the 1980s and 1990s.

These earlier Schaffner filters I replace on sight, along with RIFA capacitors,? but I am wondering if the more recent series from Schaffner had eliminated the? problem and don't need replacement.

My 3458A had just arrived back from Keysight after replacement of the A3 board and they didn't change the mains filter so I guess they don't see the newer filters as being problematic. Although, the level of support from Keysight has seemed to have gone down these days - they didn't bother changing the snap-hat batteries either even though they were well past due for replacement.

I will also check C15/C16 to see if those have been changed; I suspect not. If they are RIFA I will definitely change those.

"Chuck Harris" <cfharris@...> writes:

If you are in the USA, you will probably never witness
a Schaffner filter fail. If you are in 220-240V land, you
may not be so lucky.

When the filters fail, the worst that happens is they release
a little foul smoke, and sometimes a little tar. Both problems
are pretty easy to clean up... if they happen.

Being in the US, my policy is to leave them alone, and to
fix any that fail, when they fail. If I were in 220-240V land,
I would replace them on sight. The rivets are a simple problem.
Center punch them, drill them out, and use a fresh pop rivet
when you replace the filter.

I'm started to exchange these filters immediately before even connecting
devices to power. I'm often buying TE in the US, and what happend
several times now is that i thought "lets connect it for a short time
and see whether it works". I had it already two times that the filters
blew up a few seconds after i connected the devices. Likely because they
picked up moisture during shipment. I'm living in Germany which is 230V Land,
these days we have often 235V-240V line voltage.

In total i think i've seen now 5 filter blowing up. Not sure how many
filters i had in total, maybe 10.

Given that the filter is connected directly without any fuse to the
power outlet which usually has a 16A circuit breaker, i'm also a bit
afraid of the fire hazard.

/Sven

On 2022-09-07, at 23:10, Sven Schnelle <svens@...> wrote:

I'm started to exchange these filters immediately before even connecting
devices to power. I'm often buying TE in the US, and what happend
several times now is that i thought "lets connect it for a short time
and see whether it works”.

If I need to do such a check, I run the device from a 110 V source (*).
Smaller chance of blowing up, and 1/4 the energy if it does.

Interesting discussion, but we are not much further along pinning down any manufacturing date from which on Schaffner filters can be considered reasonably safe. Somewhere in the 1990s, apparently...

Grü?e, Carsten

(*) A Variac will do; but I can’t really imagine a lab without some 110 V devices, so I usually have a dedicated autotransformer around (which just needs to be connected the right way to phase/neutral).

On 2022-09-09, at 16:50, dbztuzujdhgtrjzthxh via groups.io <dbztuzujdhgtrjzthxh@...> wrote:

I thoroughly support replacing these filters on sight.
The first of mine that failed - it took weeks to get the smell out of the house.

Yes. And I still have tar marks on some furniture that was subjected to the jet of molten (vaporized?) tar coming out of the 3457A. Fortunately, that furniture was hard to set on fire.

The caps are only rated 250V which is ok on 110V, but no margin when used in the rest of the world.

That is a common misunderstanding of the problem.

These caps were rated for 250 V because they were designed and intended be used on 250 V mains. (250 V is the working voltage rating, not the voltage at which they start to fail — there is *plenty* of margin.)

It just turned out that the manufacturing process didn’t actually serve to protect the innards from moisture ingress in the long run, which eventually causes the caps to degrade well below their rating.
The failure then indeed happens earlier (and is more catastrophic) in 230-V-land than in 110-V-land, but the failure is the same.

Depending on climate, moisture ingress is less heavy when the device is powered (warmer than the room) continuously. Then when it is decommissioned, put into storage, and ultimately sold on ebay, the problem hits.

This doc shows what is inside and how to rebuild if you can't find a suitable replacement

www.n4iqt.com/solartron/solartron-repair.pdf

These are great images to learn more about these line filters.
But if you need to replace them, getting a new line filter is a bit less of a waste of time.
If you try to repair the line filter: Definitely do *not* get a replacement cap that is again a clear blob of hard epoxy; these will fail the same way some 20, 30 years from now. Best get one with a plastic cup and some more ductile plastic filling covering the capacitor coil.

Grü?e, Carsten

Let's be fair here, if we can...

Where an X or Y cap has a rating, that is the nominal
working voltage for the cap. The safety margin is already
cooked into the rated working voltage.

So, an X or Y cap may say 250VAC, but it is really a
much higher voltage capacitor. It is sized appropriately
to operate on a 250VAC power main.

Schaffner caps were perfectly fine when they were new, and
perfectly fine when they were quite old. But at some point
after being quite old, they failed. In droves...

The failure has nothing to do with the environment, but
rather everything to do with the epoxy used to mold the
body of the cap. Epoxy is a confused tangle of bonds that
get created as the chemicals in its mix combine. Epoxy
used to pot X or Y caps contains fillers and fire retardant
additives.

If the engineer/chemist that designed the epoxy mixture
guessed wrongly, the epoxy he designed will shrink for the
rest of time. Eventually, the tension will get so high that
the epoxy bonds break, the plastic cracks, and moisture can
get into the paper dielectric capacitor.

All paper dielectric capacitors will fail eventually if
moisture is allowed to infiltrate the paper.

-Chuck Harris


On Fri, 9 Sep 2022 14:50:38 +0000 (UTC) "dbztuzujdhgtrjzthxh via
groups.io" <dbztuzujdhgtrjzthxh@...> wrote:

I thoroughly support replacing these filters on sight.The first of
mine that failed - it took weeks to get the smell out of the
house.The caps are only rated 250V which is ok on 110V, but no margin
when used in the rest of the world.

This doc shows what is inside and how to rebuild if you can't find a
suitable replacement www.n4iqt.com/solartron/solartron-repair.pdf

"Carsten Bormann" <cabocabo@...> writes:

But if you need to replace them, getting a new line filter is a bit less of a waste of time.
If you try to repair the line filter: Definitely do *not* get a replacement cap that is again a clear blob of hard epoxy; these will fail the same way some 20, 30 years from now. Best get one with a plastic cup and some more ductile plastic filling covering the capacitor coil.

Kemet still sells metallized paper (MP) caps that appear to use the same
epoxy coating. Do we know that modern Schaffner filters have opted for
the film caps over the MP versions? Has anyone opened these up?

Also, how simple is it to open up the line filter and just replace the
caps?

Matt

I have just had two blow-ups in an 8514 and in an 8515. Nasty stink!
Does anyone know where to obtain replacements for the Schaffner mains sockets that mechanically fit?
The ones I see here in Europe are all too long. The chassis of the 851x is in the way.

Tom