Topics

OT - RIFA caps & 'transformerless' PSU


Tim Phillips
 

From Tim P (UK)
I ask here as I saw this mentioned regarding a Tek 22xx-series(?)
My problem is a Philips PM3311 which popped a RIFA capacitor, with copious
amounts of smoke. The PM3311 has this cap across what appears to be a
snubber, or just more filtering, which then applies line voltage to the
bridge rectifier. So, can I just replace the RIFA? I have checked the
bridge rectifier, bulk capacitors and other components 'downstream'.

BTW, this 'scope seems to rectify the line voltage, then modulate and
smooth it, and rectify again. I haven't investigated further, but there is
no bulky mains transformer. Rather in the way that aerospace PSUs ran at
400HZ to use smaller and lighter inductive components.

regards
Tim


Michael A. Terrell
 

That sounds like a typical switching power supply.

On Wed, Nov 4, 2020 at 7:52 AM Tim Phillips <timexucl@gmail.com> wrote:

From Tim P (UK)
I ask here as I saw this mentioned regarding a Tek 22xx-series(?)
My problem is a Philips PM3311 which popped a RIFA capacitor, with copious
amounts of smoke. The PM3311 has this cap across what appears to be a
snubber, or just more filtering, which then applies line voltage to the
bridge rectifier. So, can I just replace the RIFA? I have checked the
bridge rectifier, bulk capacitors and other components 'downstream'.

BTW, this 'scope seems to rectify the line voltage, then modulate and
smooth it, and rectify again. I haven't investigated further, but there is
no bulky mains transformer. Rather in the way that aerospace PSUs ran at
400HZ to use smaller and lighter inductive components.

regards
Tim






Tim Phillips
 

AH, yes - I've just downloaded the service manual. Makes a lot more sense
now !!
Apart from the Philips and the Tek 7704A, all my stuff is linear. Never got
round to looking at the schematics of switchers.
Thanks for the clarification.
Tim


On Wed, 4 Nov 2020 at 15:01, Michael A. Terrell <terrell.michael.a@gmail.com>
wrote:

That sounds like a typical switching power supply.

On Wed, Nov 4, 2020 at 7:52 AM Tim Phillips <timexucl@gmail.com> wrote:

From Tim P (UK)
I ask here as I saw this mentioned regarding a Tek 22xx-series(?)
My problem is a Philips PM3311 which popped a RIFA capacitor, with
copious
amounts of smoke. The PM3311 has this cap across what appears to be a
snubber, or just more filtering, which then applies line voltage to the
bridge rectifier. So, can I just replace the RIFA? I have checked the
bridge rectifier, bulk capacitors and other components 'downstream'.

BTW, this 'scope seems to rectify the line voltage, then modulate and
smooth it, and rectify again. I haven't investigated further, but there
is
no bulky mains transformer. Rather in the way that aerospace PSUs ran at
400HZ to use smaller and lighter inductive components.

regards
Tim










dave G8SFU
 

Hi Tim ...
Rifa cap are notorious for this type of failure.

Just replace it.
Dave

⁣Sent from BlueMail ​

On 4 Nov 2020, 12:52, at 12:52, Tim Phillips <timexucl@gmail.com> wrote:
From Tim P (UK)
I ask here as I saw this mentioned regarding a Tek 22xx-series(?)
My problem is a Philips PM3311 which popped a RIFA capacitor, with
copious
amounts of smoke. The PM3311 has this cap across what appears to be a
snubber, or just more filtering, which then applies line voltage to the
bridge rectifier. So, can I just replace the RIFA? I have checked the
bridge rectifier, bulk capacitors and other components 'downstream'.

BTW, this 'scope seems to rectify the line voltage, then modulate and
smooth it, and rectify again. I haven't investigated further, but there
is
no bulky mains transformer. Rather in the way that aerospace PSUs ran
at
400HZ to use smaller and lighter inductive components.

regards
Tim



Tom Lee
 

Hi Tim,

Older RIFA caps are notorious for exactly that behavior. Their plastic shrinks and cracks over time, allowing moisture to seep in, and eventually causing the magic smoke to escape explosively. My home lab still has a faint odor from the last RIFA Event, and that was over a month ago. Nasty.

Although it's ok, electrically speaking, to replace them with ordinary caps, it's best to use a proper Class-X or Class-Y safety-rated capacitor. These are designed to fail in a specific way -- as shorts or opens, respectively. Class-X is used across the line, Class-Y from line to neutral. I don't have a schematic of that scope before me, so I don't know for sure where your cap sits. Just be sure to order the right type for your circuit if you want to maintain safety as originally intended.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 11/4/2020 04:52, Tim Phillips wrote:
From Tim P (UK)
I ask here as I saw this mentioned regarding a Tek 22xx-series(?)
My problem is a Philips PM3311 which popped a RIFA capacitor, with copious
amounts of smoke. The PM3311 has this cap across what appears to be a
snubber, or just more filtering, which then applies line voltage to the
bridge rectifier. So, can I just replace the RIFA? I have checked the
bridge rectifier, bulk capacitors and other components 'downstream'.

BTW, this 'scope seems to rectify the line voltage, then modulate and
smooth it, and rectify again. I haven't investigated further, but there is
no bulky mains transformer. Rather in the way that aerospace PSUs ran at
400HZ to use smaller and lighter inductive components.

regards
Tim




Carsten Bormann
 

On 2020-11-04, at 14:02, dave G8SFU via groups.io <djk302=zoho.com@groups.io> wrote:

Just replace it.
Let me amplify that a bit: Replace on sight (inside and outside main filters).
Don’t even think of keeping them under power (they might be located before the main power switch!).

If you need a little more graphic motivation (yes, it happened twice to the same guy in as much as a couple of months — you live, you learn :-):

https://youtu.be/xodwAeGD9kc?t=852s
"#193 Who let the SMOKE out ! HP 8904A Multifunction Synthesizer Repair Part 1 - YouTube"
https://youtu.be/c2dgI7duA7w?t=840
"#212 Behold the MAGIC SMOKE !! HP 8647A First Look, Blown up and Repaired - YouTube"
https://youtu.be/XAbrU17hLTM?t=160
"EEVblog #1183 - RIFA Madness (Schaffner Repair) - YouTube”

What these videos can't show is that your nose doesn’t want to return to that room for a month or so. The ejected material might also land on unrelated objects (e.g., behind a line filter), soil them, set them alight, ...

If the caps are marked X or Y (as they always are in a line filter), do replace them with the same class of safety capacitor.
Bad replacements for X capacitors can burn down your house, while bad replacements for Y capacitors can kill you outright. Don’t skimp on these.

RIFA capacitors do explode more readily and more violently in 230 V systems than in 110 V systems, but don’t think you are safe on 110 V.

(WIMA built the same kind of capacitors, by the way; this is about caps in blobs of yellowish/golden transparent epoxy that tends to crack or turn crazed, not just the company RIFA, which just happens to be most famous for producing these before they went out of fashion.)

Grüße, Carsten

(I still have a couple HP 3457A and a Solartron 7150 that need them fixed…
I also have an HP 8647A… One of these days…)


Jim Ford
 

Yep, I'm in the process of replacing an X2 rated 0.1 uF RIFA in my 1989 HP 8350B sweep oscillator, before it goes kaboom.  I replaced the whole power inlet/fuse holder/EMI filter but then found ceramic Y caps inside; I suppose the whole thing didn't need to be replaced.  Oh well.  More test equipment pieces to check still...Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Carsten Bormann <cabocabo@gmail.com> Date: 11/4/20 2:18 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] OT - RIFA caps & 'transformerless' PSU On 2020-11-04, at 14:02, dave G8SFU via groups.io <djk302=zoho.com@groups.io> wrote:> > Just replace it.Let me amplify that a bit:  Replace on sight (inside and outside main filters). Don’t even think of keeping them under power (they might be located before the main power switch!).If you need a little more graphic motivation (yes, it happened twice to the same guy in as much as a couple of months — you live, you learn :-):https://youtu.be/xodwAeGD9kc?t=852s";#193 Who let the SMOKE out ! HP 8904A Multifunction Synthesizer Repair Part 1 - YouTube"https://youtu.be/c2dgI7duA7w?t=840";#212 Behold the MAGIC SMOKE !! HP 8647A First Look, Blown up and Repaired - YouTube"https://youtu.be/XAbrU17hLTM?t=160";EEVblog #1183 - RIFA Madness (Schaffner Repair) - YouTube”What these videos can't show is that your nose doesn’t want to return to that room for a month or so.  The ejected material might also land on unrelated objects (e.g., behind a line filter), soil them, set them alight, ...If the caps are marked X or Y (as they always are in a line filter), do replace them with the same class of safety capacitor.Bad replacements for X capacitors can burn down your house, while bad replacements for Y capacitors can kill you outright.  Don’t skimp on these.RIFA capacitors do explode more readily and more violently in 230 V systems than in 110 V systems, but don’t think you are safe on 110 V.(WIMA built the same kind of capacitors, by the way; this is about caps in blobs of yellowish/golden transparent epoxy that tends to crack or turn crazed, not just the company RIFA, which just happens to be most famous for producing these before they went out of fashion.)Grüße, Carsten(I still have a couple HP 3457A and a Solartron 7150 that need them fixed…I also have an HP 8647A…  One of these days…)


Brian Symons
 

A good reason to wear safety glasses too.
When components go bang that shrapnel can embed itself in your skin so you don't want it in your eyes.

Another component that can go bang is surge diverters.
Some items have surge diverters fitted across terminals or on printed circuits.
I always wondered why some of them had heatshrink sleeves fitted over them.

I then worked on a piece of equipment that the house had a nearby lightning strike.
Not on the property but to a close one.
I had the item powered up for a while while testing when all of a sudden - BANG!!!

I had pieces of the surge diverter stuck in my face & hands. Some bits had to be dug out.

A few months later it happened again.  It actually dinged the metalwork beside the surge diverter & damaged the PCB.
I've seen PCBs that the surge diverters have exploded on but heatshrink sleeves have restrained the shrapnel & prevented any damage.

I always fit heatshrink sleeves now BEFORE I power any item on.

Regards,
Brian.


greenboxmaven
 

A good tale I can relate was in 1968. I was working at a TV shop that did warranty repairs for several furniture stores. One afternoon, we got four identical TVs for repair. Nothing was said about what was wrong with them, so I removed the back cover from one, connected a cheater cord ( does anyone remember those?), and plugged it in. The bench outlets were on a 20 amp breaker because we also did electrical repairs on window air conditioners. The result was a BLAM! that left everyone's ears ringing. The condenser across the power in connector had let go. After the smoke cleared and I replaced the condenser with a good quality 600 volt one, as the schematic specified, the set came one and worked perfectly. Now aware and forewarned, the other three did the same thing and received the same repair. We found out the manufacturer had produced many sets with the wrong condenser, and they were very happy to pay our repair time tickets. Those of us young at heart had a bit of fun that afternoon. We all had the habit of making sure we were not grounded to anything, using only one hand to plug in or power up, and turning away and closing our eyes the first time.

Bruce Gentry, KA2IVY

On 11/5/20 7:05 AM, Brian Symons wrote:
A good reason to wear safety glasses too.
When components go bang that shrapnel can embed itself in your skin so you don't want it in your eyes.

Another component that can go bang is surge diverters.
Some items have surge diverters fitted across terminals or on printed circuits.
I always wondered why some of them had heatshrink sleeves fitted over them.

I then worked on a piece of equipment that the house had a nearby lightning strike.
Not on the property but to a close one.
I had the item powered up for a while while testing when all of a sudden - BANG!!!

I had pieces of the surge diverter stuck in my face & hands. Some bits had to be dug out.

A few months later it happened again. It actually dinged the metalwork beside the surge diverter & damaged the PCB.
I've seen PCBs that the surge diverters have exploded on but heatshrink sleeves have restrained the shrapnel & prevented any damage.

I always fit heatshrink sleeves now BEFORE I power any item on.

Regards,
Brian.






Stephen Hanselman
 

What he said! I have a HP 8663 whose surge protectors stuck little bits in the big filter caps.

Saftey glasses are not just for looks.

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Nov 5, 2020, at 04:06, Brian Symons <brians@mackay.net.au> wrote:

A good reason to wear safety glasses too.
When components go bang that shrapnel can embed itself in your skin so you don't want it in your eyes.

Another component that can go bang is surge diverters.
Some items have surge diverters fitted across terminals or on printed circuits.
I always wondered why some of them had heatshrink sleeves fitted over them.

I then worked on a piece of equipment that the house had a nearby lightning strike.
Not on the property but to a close one.
I had the item powered up for a while while testing when all of a sudden - BANG!!!

I had pieces of the surge diverter stuck in my face & hands. Some bits had to be dug out.

A few months later it happened again. It actually dinged the metalwork beside the surge diverter & damaged the PCB.
I've seen PCBs that the surge diverters have exploded on but heatshrink sleeves have restrained the shrapnel & prevented any damage.

I always fit heatshrink sleeves now BEFORE I power any item on.

Regards,
Brian.






Brian Cockburn
 


Lawrance A. Schneider
 

At the present time, I can get to my equipment - so, I was wondering did HP put this type of capacitor on their equipment? If so, should each and everyone be replaced?

In general, should these be replaced anytime you encounter one?

Thanks, larry


Carsten Bormann
 

On 2020-11-07, at 14:31, Lawrance A. Schneider <llaassllaaass@gmail.com> wrote:

At the present time, I can get to my equipment - so, I was wondering did HP put this type of capacitor on their equipment?
I’m not sure I understand this sentence, but I’m sure at the time HP (or the supplier HP relied on, e.g., Schaffner) speced these, the failure mode was not known. Other manufacturers did the same. I haven’t been able to precisely delimit the time frame over which this was a problem, but, e.g., a Schaffner filter from this century won’t have these types of caps any more.

If so, should each and everyone be replaced?

In general, should these be replaced anytime you encounter one?
Anything that is potentially connected to high-energy sources (line filters, snubbers etc.): Yes.
(You’d need good knowledge of the circuit to rule this out, so maybe the answer is a “Yes” in general.)
Note that these may be buried in high-quality line filters (e.g., from Schaffner), so any line filter from that period is suspect.

Grüße, Carsten


Tom Lee
 

HP used (and still uses) RIFA caps, but they weren't the only one. Apple used them, for example (and perhaps still does). My first Mac (a Plus from the late 1980s) had one, and it exploded spectacularly.

Cracking of the plastics is readily visible. Those are the caps that will explode, perhaps soon, perhaps not (it depends on many external factors, humidity perhaps chief among them). Whether it's crack or not, if I see a RIFA in the yellowish plastic package, out it goes. It's on my standard to-do list whenever opening up an instrument.

RIFA changed their formula sometime in the late 90s, it seems. The old translucent yellowish plastic is now gone. The plastic in the newer RIFA caps is opaque. These new ones, I am told, are very good. All I can say is that I have not had any of those explode on me, but they are also newer. Time will tell, I guess.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 11/7/2020 05:31, Lawrance A. Schneider wrote:
At the present time, I can get to my equipment - so, I was wondering did HP put this type of capacitor on their equipment? If so, should each and everyone be replaced?

In general, should these be replaced anytime you encounter one?

Thanks, larry




Brad Thompson
 

Tom Lee wrote on 11/7/2020 1:40 PM:

HP used (and still uses) RIFA caps, but they weren't the only one. Apple used them, for example (and perhaps still does). My first Mac (a Plus from the late 1980s) had one, and it exploded spectacularly.

Cracking of the plastics is readily visible. Those are the caps that will explode, perhaps soon, perhaps not (it depends on many external factors, humidity perhaps chief among them). Whether it's crack or not, if I see a RIFA in the yellowish plastic package, out it goes. It's on my standard to-do list whenever opening up an instrument.

RIFA changed their formula sometime in the late 90s, it seems. The old translucent yellowish plastic is now gone. The plastic in the newer RIFA caps is opaque. These new ones, I am told, are very good. All I can say is that I have not had any of those explode on me, but they are also newer. Time will tell, I guess.
Hello--

IIRC, these capacitors featured a metallized-paper dielectric which had a "self healing" property--
i.e., a transient overvoltage that caused a  puncture of the dielectric
 would vaporize the metal coating and clear the momentary short circuit.

Unfortunately, cracks in the encapsulant allowed moisture to infiltrate the
paper dielectric, which became conductive... and then the fun began<g>.

Crack-proof encapsulant reportedly solved the problem.

73--

Brad  AA1IP


-
 

"At the present time, I can get to my equipment - so, I was wondering did
HP put this type of capacitor on their equipment? If so, should each and
everyone be replaced?

In general, should these be replaced anytime you encounter one?"

I would. About ten years ago I pulled out a bunch of HP 1000 computers
that had been in storage for about 6 or 8 years. The RIFA caps exploded in
every one of them over the course of several hours to several days after
powering them up. All together about 14 computers and another 18 power
supplies. Other than cleaning some dirty CCA contacts, the RIFA caps were
the only thing in the computers that failed.

On Sat, Nov 7, 2020 at 8:31 AM Lawrance A. Schneider <
llaassllaaass@gmail.com> wrote:

At the present time, I can get to my equipment - so, I was wondering did
HP put this type of capacitor on their equipment? If so, should each and
everyone be replaced?

In general, should these be replaced anytime you encounter one?

Thanks, larry






Carsten Bormann
 

On 2020-11-07, at 23:07, - <rrrr6789@gmail.com> wrote:

I would. About ten years ago I pulled out a bunch of HP 1000 computers
that had been in storage for about 6 or 8 years. The RIFA caps exploded in
every one of them over the course of several hours to several days after
powering them up.
Ugh. Was the property you did this in condemned after all this stink?

Protip: In line filters, you can just unsolder the RIFA caps and run the unit without them during the time when you acquire new safe caps that physically fit (and are electrically within an order of magnitude).

(Don’t do that with snubbers, though. How do you know? There are other components around snubbers, while line filters are often right on the phase and neutral leads. If you are forced to run the unit with an unreplaced RIFA cap in a snubber, order replacements for those components as well because they will play the role of a fuse.)

Grüße, Carsten


Lawrance A. Schneider
 

On Sat, Nov 7, 2020 at 11:35 AM, Carsten Bormann wrote:



At the present time, I can get to my equipment - so, I was wondering did
HP put this type of capacitor on their equipment?
I’m not sure I understand this sentence,
I was not a home at the time I wrote it. When I got home, I cannot open each case and look as I have other obligations the must come first.

Thus, my question was for planning purposes. I have a Tek 2465 & 2465BDM. I have HP E3630A, 3312A, 8112A, 8116A, 8594E (which I hope to sell). Should I buy new caps for each and plan on working on each piece of equipment to avoid 'the explosion' of which I had NO idea before Mr. Phillips posted his query.

Note that these may be buried in high-quality line filters (e.g., from Schaffner), so
any line filter from that period is suspect.
WOW!!!!! Now I hope someone like Mr. Harris or others with encyclopedic knowledge of these instruments has some idea of the time frame of which you wrote.

Danke, larry


Carsten Bormann
 

On 2020-11-07, at 23:07, - <rrrr6789@gmail.com> wrote:

About ten years ago I pulled out a bunch of HP 1000 computers
that had been in storage for about 6 or 8 years. The RIFA caps exploded in
every one of them over the course of several hours to several days after
powering them up. All together about 14 computers and another 18 power
supplies. Other than cleaning some dirty CCA contacts, the RIFA caps were
the only thing in the computers that failed.
If you are longing to repeat the experience:

https://www.ebay.de/itm/333171770198

You can’t make this up.

Grüße, Carsten


 

I have a long history with Rifa PME271 X2 caps.
Actually, an explosive history.
My standard replacement is the Vishay 338x or 339 series - much higher voltage ratings at 310VAC and 440VAC.

Replacement limitations advice:
X2 may be replaced by X2 or X1 (higher spec), or Y2 or Y1
X1 may be replaced by X1 or Y1
Y2 may be replaced by Y2 or Y1
Y1 may be replaced by only Y1

Y1 or Y2 may NEVER be replaced by X1 or X2.

Always a good idea to select a replacement with a HIGHER AC voltage rating, than the original's.