explosion mystery on my 7104


Sparky99
 

I powered by 7104 on this evening. After about 30 minutes I hear a loud squealing noise (imagine steam escaping from a boiling kettle) coming from the back of the instrument and immediately sensed a very intense burning / smoke smell - the kind I would usually associated with electrolytic caps that let go, but only seemingly stronger. My house RCD for the circuit the scope is on also tripped about the same time that I turned the scope off.
Fearing the worst I unplugged the scope, reset the RCD and took a look at the back - only to be met with a mystery. The cooling fin nearest the mains IEC connector was covered with a dark brown guey substance which had run down to the lower end of the fin. The other side of the IEC connector was blackened with dust and some goo. The IEC connector itself was oddly empty of any goo or particles, seemingly indicating that whatever caused the "explosion" was external to the inner part of the connector at least. The force of the explosion was such that the wall behind the scope was also covered with debris - small blackened parties and a light coating of dark brown residue. The mains fuse of the scope was intact.
The fuse, RCD and external nature of the guey and blackened areas all indicate that it was something external to the scope which caused the problem - but what? I have not tried powering the scope on yet, will wait until tomorrow for that - I am already in quite some trouble tonight with my wife :). Any thoughts on what might have caused the explosion? I considered insects, but the amount of goo suggest something unusually large, and also I don't understand how they could have caused current to flow between the live and earth conductors (thus tripping the RCD) as the IEC connector is reasonably well sealed when plugged in - especially from the kind of large bugs that would contain sufficient "goo". Has anyone got any ideas or theories on this?

Sparky 99


 

The mains input filter or a mains filter cap has blown. Very common problem, nothing serious, just messy. Happens most often in 230...240VAC
countries.

Raymond


 

On Fri, Jun 18, 2021 at 12:32 AM, Raymond Domp Frank wrote:


The mains input filter or a mains filter cap has blown. Very common problem,
nothing serious, just messy. Happens most often in 230...240VAC countries.
Hi Julian,
You'll find many references to this problem, its cause and how to repair your 'scope, on this group and others. It takes quite bit of work with these 'scopes: It'll be necessary to remove the switching power supply and (AFAIR) open it. On the other hand, your 'scope will operate even with the circuit blown as it is. Usually, once it's blown, it's blown all the way, so you won't be disturbed by more noises, smoke and smell. There's no harm in using the 'scope as is, strange as it may sound. EMC (noise in and out) will probably be worse but many people don't really care about that. Real lovers of this old equipment will want to repair it though.
Cleaning up the mess in the 'scope usually is quite a hassle.

Raymond


 

On Fri, Jun 18, 2021 at 01:47 AM, Raymond Domp Frank wrote:


You'll find many references to this problem, its cause and how to repair your
'scope, on this group and others.
Julian,
Google "Blown Rifa cap", "Blown (Schaffner) mains filter" and the like. You'll be met by dozens of descriptions of these cases.

Raymond


Jean-Paul
 

Cracked plastic encapsulant.

Much worse problem on 240 V mains, have yet to see the Rifa X/Y line filter cap issue on a 120V mains

Jon


redarlington
 

In the Apple II community, we call this RIFA Madness. It's exceptionally
common that those Rifa line filter caps blow here in the States with our
120v lines. We either replace before powering up old equipment, cut em
out, or deal with a cleanup if we ignore them.

-Bob N3XKB

On Thu, Jun 17, 2021 at 10:56 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:

Cracked plastic encapsulant.

Much worse problem on 240 V mains, have yet to see the Rifa X/Y line
filter cap issue on a 120V mains

Jon






Roy Thistle
 

On Fri, Jun 18, 2021 at 09:22 AM, redarlington wrote:


It's exceptionally
common that those Rifa line filter caps blow here in the States with our
120v lines.
I dunno... if it was "exceptionally common" I would have seen it... or heard about it here... in the colonies... as we have have a nominal 120 V system here too... and I've got those X or Y Rifa caps, in Apple II smps... as well as in HP... and I think Tek too.
It makes a lot of sense to say they are more common to fail in places where the nominal voltage is 230 volts or 240 volts... as many of them were clearly rated for 250V.
AFAIC a lot of it is pure flummery meant to flummox "capacitor replacement kiddies" ... who ape YouTube profiteers.
Not saying it can't happen... if the cracked RIFAs get wet enough... they could cascade short... but I agree with other posters... it's only common on YouTube.
--
Roy Thistle


-
 

Roy, that's not true. About 15 years ago I obtained 13 E and F series HP
1000 computers and 8 extra power supplies from a large US military
contractor. I powered them up and the RIFA caps blew up in about 70% of
them within minutes or up to about 2 days after I powered them up. All of
these units had been under a maintenance contract with HP up until the time
that they were removed from service and placed in inside dry storage and
everything was 100% functional when it was placed in storage. I don't know
if the problem is due to the brand of RIFA cap, or the particular model or
just a particular batch or related to being stored unused for a period of
time, but exploding RIFA caps are a KNOWN issue. I've had RIFA caps explode
in other HP equipment as well but never in the numbers that they did in
those HP computers. In fact I have owned hundreds of HP 9000 and 98xx
series computers (EVERY generation) and I've never had a RIFA cap explode
in any of them.

On Fri, Jun 18, 2021 at 2:10 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

On Fri, Jun 18, 2021 at 09:22 AM, redarlington wrote:


It's exceptionally
common that those Rifa line filter caps blow here in the States with our
120v lines.
I dunno... if it was "exceptionally common" I would have seen it... or
heard about it here... in the colonies... as we have have a nominal 120 V
system here too... and I've got those X or Y Rifa caps, in Apple II smps...
as well as in HP... and I think Tek too.
It makes a lot of sense to say they are more common to fail in places
where the nominal voltage is 230 volts or 240 volts... as many of them were
clearly rated for 250V.
AFAIC a lot of it is pure flummery meant to flummox "capacitor replacement
kiddies" ... who ape YouTube profiteers.
Not saying it can't happen... if the cracked RIFAs get wet enough... they
could cascade short... but I agree with other posters... it's only common
on YouTube.
--
Roy Thistle






Tom Lee
 

A quick google turns up many posts attesting to the RIFA problem. The mains voltage matters little. Many members of this list who live in 120V lands have experienced the multimedia spectacular that is the exploding RIFA cap.

Tom

Sent from my iThing, so please forgive brevity and typos

On Jun 18, 2021, at 11:38, - <rrrr6789@gmail.com> wrote:

Roy, that's not true. About 15 years ago I obtained 13 E and F series HP
1000 computers and 8 extra power supplies from a large US military
contractor. I powered them up and the RIFA caps blew up in about 70% of
them within minutes or up to about 2 days after I powered them up. All of
these units had been under a maintenance contract with HP up until the time
that they were removed from service and placed in inside dry storage and
everything was 100% functional when it was placed in storage. I don't know
if the problem is due to the brand of RIFA cap, or the particular model or
just a particular batch or related to being stored unused for a period of
time, but exploding RIFA caps are a KNOWN issue. I've had RIFA caps explode
in other HP equipment as well but never in the numbers that they did in
those HP computers. In fact I have owned hundreds of HP 9000 and 98xx
series computers (EVERY generation) and I've never had a RIFA cap explode
in any of them.

On Fri, Jun 18, 2021 at 2:10 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

On Fri, Jun 18, 2021 at 09:22 AM, redarlington wrote:


It's exceptionally
common that those Rifa line filter caps blow here in the States with our
120v lines.
I dunno... if it was "exceptionally common" I would have seen it... or
heard about it here... in the colonies... as we have have a nominal 120 V
system here too... and I've got those X or Y Rifa caps, in Apple II smps...
as well as in HP... and I think Tek too.
It makes a lot of sense to say they are more common to fail in places
where the nominal voltage is 230 volts or 240 volts... as many of them were
clearly rated for 250V.
AFAIC a lot of it is pure flummery meant to flummox "capacitor replacement
kiddies" ... who ape YouTube profiteers.
Not saying it can't happen... if the cracked RIFAs get wet enough... they
could cascade short... but I agree with other posters... it's only common
on YouTube.
--
Roy Thistle









n4buq
 

I'm in 125V land and a RIFA released smoke in my 2445 but it didn't have the violent eruption described by others. I was kind of disappointed... :)

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: TekScopes@groups.io
Sent: Friday, June 18, 2021 1:54:30 PM
Subject: Re: [TekScopes] explosion mystery on my 7104

A quick google turns up many posts attesting to the RIFA problem. The mains
voltage matters little. Many members of this list who live in 120V lands
have experienced the multimedia spectacular that is the exploding RIFA cap.

Tom

Sent from my iThing, so please forgive brevity and typos

On Jun 18, 2021, at 11:38, - <rrrr6789@gmail.com> wrote:

Roy, that's not true. About 15 years ago I obtained 13 E and F series HP
1000 computers and 8 extra power supplies from a large US military
contractor. I powered them up and the RIFA caps blew up in about 70% of
them within minutes or up to about 2 days after I powered them up. All of
these units had been under a maintenance contract with HP up until the time
that they were removed from service and placed in inside dry storage and
everything was 100% functional when it was placed in storage. I don't know
if the problem is due to the brand of RIFA cap, or the particular model or
just a particular batch or related to being stored unused for a period of
time, but exploding RIFA caps are a KNOWN issue. I've had RIFA caps explode
in other HP equipment as well but never in the numbers that they did in
those HP computers. In fact I have owned hundreds of HP 9000 and 98xx
series computers (EVERY generation) and I've never had a RIFA cap explode
in any of them.

On Fri, Jun 18, 2021 at 2:10 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

On Fri, Jun 18, 2021 at 09:22 AM, redarlington wrote:


It's exceptionally
common that those Rifa line filter caps blow here in the States with our
120v lines.
I dunno... if it was "exceptionally common" I would have seen it... or
heard about it here... in the colonies... as we have have a nominal 120 V
system here too... and I've got those X or Y Rifa caps, in Apple II
smps...
as well as in HP... and I think Tek too.
It makes a lot of sense to say they are more common to fail in places
where the nominal voltage is 230 volts or 240 volts... as many of them
were
clearly rated for 250V.
AFAIC a lot of it is pure flummery meant to flummox "capacitor replacement
kiddies" ... who ape YouTube profiteers.
Not saying it can't happen... if the cracked RIFAs get wet enough... they
could cascade short... but I agree with other posters... it's only common
on YouTube.
--
Roy Thistle













Roy Thistle
 

On Fri, Jun 18, 2021 at 11:39 AM, - wrote:


that's not true. About 15 years ago I obtained 13 E and F series HP
1000 computers and 8 extra power supplies from a large US military
contractor.
Yup. If the equipment was stored where the humidity was high... which is not proper storage... then the cracked Rifa capacitors... or any case damaged X/Y cap could absorb moisture... and could short.
The thing to do before you power on equipment is to make sure its thoroughly dry... and that means enough time in a dry environment.
That includes Apple stuff... and stuff from the dump.

--
Roy Thistle


Roy Thistle
 

On Fri, Jun 18, 2021 at 11:54 AM, Tom Lee wrote:


A quick google turns up many posts
Hi Dr. Tom:
Well a quick search on the net turns up many posts about eye witness accounts of Yeti too.
If you have the time, and you want to: what's your explanation of why the voltage does not factor into it?
It seems to me it does.


--
Roy Thistle


Tom Lee
 

The point is that RIFA caps of that era crack at high rates. “Dry storage” is not the solution. That should be obvious.

Sent from my iThing, so please forgive brevity and typos

On Jun 18, 2021, at 13:34, Roy Thistle <roy.thistle@mail.utoronto.ca> wrote:

On Fri, Jun 18, 2021 at 11:39 AM, - wrote:


that's not true. About 15 years ago I obtained 13 E and F series HP
1000 computers and 8 extra power supplies from a large US military
contractor.
Yup. If the equipment was stored where the humidity was high... which is not proper storage... then the cracked Rifa capacitors... or any case damaged X/Y cap could absorb moisture... and could short.
The thing to do before you power on equipment is to make sure its thoroughly dry... and that means enough time in a dry environment.
That includes Apple stuff... and stuff from the dump.

--
Roy Thistle





Roy Thistle
 

Hi N4bug:
Sorry you didn't get to have the experience.
But, my reply was to the claim that it's "exceptionally common" ... not that people have not had it happen to them.
IMO it is not "exceptionally common" and that it does.. well that's as they say a meme (although that term is often misused.)
There's a lot of old Tek and HP equipment... and I'm willing to think that compared to the amount of it... it's rare that the XY class caps fail in such a way as the OP described... unless it being stored improperly, as in humid environments.
The Rifa case on those caps do crack and craze. I've got them doing that in equipment here. But, they are working fine.
So cracking of the Rifa case could be the distal cause... depending on how you look at it.
I suggest the proximal cause is the absorbed moisture... with the cap working at higher voltages... but, not only... get enough moisture, for long enough... and perhaps it doesn't take much of a surge to cause a short.

--
Roy Thistle


redarlington
 

So to follow up, I should've quantified what I meant by exceptionally
common. In my world it's so common we have memes about those RIFA caps
popping. Yes, they crack and that's the big sign to check for before
replacing them. They're gonna pop. I'm not a fan of blindly swapping out
parts before they show signs of degrading. The problem is, they show signs
after all these years. I'm sure we can all find counterexamples. I'm
talking about my experience in my world, this happens so often that it gets
annoying just to read about it, so we have to joke about it. Maybe Apple
got the shaft. Maybe it was a bad run for... 10 years. I don't know.
Guys, have fun. Apologies for the distraction.

-Bob N3XKB

On Fri, Jun 18, 2021 at 3:02 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:


Hi N4bug:
Sorry you didn't get to have the experience.
But, my reply was to the claim that it's "exceptionally common" ... not
that people have not had it happen to them.
IMO it is not "exceptionally common" and that it does.. well that's as
they say a meme (although that term is often misused.)
There's a lot of old Tek and HP equipment... and I'm willing to think that
compared to the amount of it... it's rare that the XY class caps fail in
such a way as the OP described... unless it being stored improperly, as in
humid environments.
The Rifa case on those caps do crack and craze. I've got them doing that
in equipment here. But, they are working fine.
So cracking of the Rifa case could be the distal cause... depending on how
you look at it.
I suggest the proximal cause is the absorbed moisture... with the cap
working at higher voltages... but, not only... get enough moisture, for
long enough... and perhaps it doesn't take much of a surge to cause a short.

--
Roy Thistle






stevenhorii
 

With that failure rate in those HP1000 computers, it would make me wonder
if, since they came from a US military contractor, if the computers had
been purchased on a contract by them as a lot. That makes it more likely
that they were manufactured by HP at about the same time. Maybe a bad lot
of Rifa capacitors?

Also, I have some equipment with capacitors that look like the Rifas but
are marked with the Philips name and part number. Are they just made by
Evox Rifa for Philips or are they made by Philips? Does anyone know? The
capacitors look fine - no cracked or discolored cases.

Steve Horii

On Fri, Jun 18, 2021 at 14:39 - <rrrr6789@gmail.com> wrote:

Roy, that's not true. About 15 years ago I obtained 13 E and F series HP
1000 computers and 8 extra power supplies from a large US military
contractor. I powered them up and the RIFA caps blew up in about 70% of
them within minutes or up to about 2 days after I powered them up. All of
these units had been under a maintenance contract with HP up until the time
that they were removed from service and placed in inside dry storage and
everything was 100% functional when it was placed in storage. I don't know
if the problem is due to the brand of RIFA cap, or the particular model or
just a particular batch or related to being stored unused for a period of
time, but exploding RIFA caps are a KNOWN issue. I've had RIFA caps explode
in other HP equipment as well but never in the numbers that they did in
those HP computers. In fact I have owned hundreds of HP 9000 and 98xx
series computers (EVERY generation) and I've never had a RIFA cap explode
in any of them.

On Fri, Jun 18, 2021 at 2:10 PM Roy Thistle <roy.thistle@mail.utoronto.ca>

On Fri, Jun 18, 2021 at 09:22 AM, redarlington wrote:


It's exceptionally
common that those Rifa line filter caps blow here in the States with
our
120v lines.
I dunno... if it was "exceptionally common" I would have seen it... or
heard about it here... in the colonies... as we have have a nominal 120 V
system here too... and I've got those X or Y Rifa caps, in Apple II
smps...
as well as in HP... and I think Tek too.
It makes a lot of sense to say they are more common to fail in places
where the nominal voltage is 230 volts or 240 volts... as many of them
were
clearly rated for 250V.
AFAIC a lot of it is pure flummery meant to flummox "capacitor
replacement
kiddies" ... who ape YouTube profiteers.
Not saying it can't happen... if the cracked RIFAs get wet enough... they
could cascade short... but I agree with other posters... it's only common
on YouTube.
--
Roy Thistle










Roy Thistle
 

On Fri, Jun 18, 2021 at 02:07 PM, redarlington wrote:


Apologies for the distraction
Hi N3XKB:
Well it's not a distraction for me. And, I'm glad you offered your input.
I've got those Rifa caps in stuff here, and they have cracked/crazed... and yet the stuff has been working for a long time.
I don't want to have a mass evacuation of RIFA smoke... so I'm interested.


--
Roy Thistle


Sparky99
 

Hi everyone, thanks for helping me out on this - I removed the power supply in the 7104 (which is a very late model from 88/89) today and even after removing the covers it looks clean. There is one Rifa cap which has a cracked case and which following the advice on here I will replace, but the really odd thing is that everything else looks intact. It makes no sense as on the back of the scope there was a brown tar like goo, and blackened powder - which had even been deposited onto the wall behind the scope. The only way it could have got onto the scope at the back where it is is through the cut-out for the mains IEC connector, but this seems clean. All the symptoms are cap like, but it really looks as though its non of the internal components. I'll investigate further tomorrow and try powering it up again - so at the moment, still a mystery!

Julian


Stephen Bell
 

My experience with RIFA mains capacitors of that era is that they are all ticking time bombs and will eventually fail. I immediately replace RIFA capacitors whenever I find them, whether they have crazed cases or not. After replacing them I also check their insulation resistance and find that most are below 1Mohm.

I don't think the answer is just storing the equipment a low humidity environment. The area where I live has quite a dry climate and the indoor RH is typically only 50% but I still see failures and low insulation resistance with these capacitors. To get any useful improvement I think the storage RH would have to be considerably reduced, which makes for an unpleasant working environment for people plus generating a greatly increased risk of static electricity build-up.


Stephen Bell
 

Closely examine the mains inlet filter, particularly if it is a Schaffner brand.

I have seen, and heard, these fail in spectacular fashion leaving a surrounding deposit of sticky, and extremely smelly, black goo. The filter itself can still appear relatively intact after such an incident but close examination will probably reveal a small hole where the filter's potting compound has been violently expelled.