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Retrospective fright
Retrospective fright
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Old 20th August 2019, 04:54 PM   #1
Elvee is offline Elvee  Belgium
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Default Retrospective fright

I wanted to illustrate this thread with an example of mains pass-through box, and I remembered that a section of the mains distribution of my lab was equipped with a filter, housed in such a box.

Retrospective fright-cancelcase-jpg

This section is unswitched, thus permanently connected to the mains, and I use it for low power, sensitive instruments, like active probes, distortionmeter, etc.

I thus removed the box to take a snapshot, and I noticed a funny smell.

I took the picture and left it on my desk, but the smell didn't go away and became more and more present.

In the end, suspecting an anomaly, I opened the box and here is what I found:

Retrospective fright-schaff1-jpg

The filter has overheated, and the hot gases inside the case reached such a pressure that it visibly bulged:

Retrospective fright-schaff2-jpg

Fortunately, the gases were able to escape through the wires passages, and the case didn't burst, which would have been catastrophic and could have caused a fire.

Yet, the filter is from a reputable maker:

Retrospective fright-schaff3-jpg

I am almost certain that a paper cap caused the incident, which could have had dramatic consequences.
I have no idea when it happened, the smell was only noticeable from a very short distance.
Thus, beware of paper caps!
Attached Images
File Type: jpg CancelCase.jpg (138.3 KB, 135 views)
File Type: jpg Schaff1.jpg (281.5 KB, 133 views)
File Type: jpg Schaff2.jpg (247.2 KB, 130 views)
File Type: jpg Schaff3.jpg (239.4 KB, 137 views)
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Old 20th August 2019, 05:00 PM   #2
rayma is online now rayma  United States
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Also recently, an X capacitor in a customer's amplifier that I built over 40 years ago started smoking.
He was kind of freaked out, and since he was far away, I asked him to just cut the bad part out.
Not sure if it was paper.

Last edited by rayma; 20th August 2019 at 05:02 PM.
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Old 20th August 2019, 11:52 PM   #3
Refugee1 is offline Refugee1  United Kingdom
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Those filter blocks have a RIFA capacitor embedded inside them.
They fail with a lot of very smelly smoke after about 15 years regardless of how many hours of use they have had.
Just replace the thing every 10 years.
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Old 21st August 2019, 02:25 AM   #4
PRR is offline PRR  United States
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I bet that thing is 31 years old.
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Old 21st August 2019, 12:17 PM   #5
Pano is offline Pano  United States
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Retrospective fright
That's rather specific. Why 31?
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Old 21st August 2019, 12:27 PM   #6
Tubelab_com is offline Tubelab_com  United States
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Quote:
That's rather specific. Why 31?
There is an 8831 date code on it. That would be the 31st week of 1988.
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Old 21st August 2019, 12:34 PM   #7
Refugee1 is offline Refugee1  United Kingdom
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That clearly takes it well past my use by date.
They often set off fire alarms when they go up in a puff of smoke.
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Old 21st August 2019, 12:58 PM   #8
Kay Pirinha is offline Kay Pirinha  Germany
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I'm still wondering why X2 RFI supression caps just by RIFA tend to fail catastrophically after some years. We know this issue very well from old Dual TT's, as RIFA capacitors were very common in them.
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Old 28th August 2019, 08:57 PM   #9
MarsBravo is offline MarsBravo  Netherlands
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Quote:
Originally Posted by PRR View Post
I bet that thing is 31 years old.
Spot on!
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Old 28th August 2019, 08:58 PM   #10
MarsBravo is offline MarsBravo  Netherlands
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Quote:
Originally Posted by Tubelab_com View Post
There is an 8831 date code on it. That would be the 31st week of 1988.
Perfect nailed!!!
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