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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 4th Sep 2021, 1:45 am   #1
joebog1
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Default Pre-failed Class X2 Capacitors.

A friend recently bought out a business that had gone down. Literally 100's of thousands of components, all new and in original manufacturers packaging.

We were looking to make some filters for his recording studio, and were making switch snubbers to stop the annoying clicks and pops caused by glitches on the mains.

WE found a bag of 2000 0.1 uF 275 volts AC rated X2 caps and fitted them to various bits of equipment ( mostly old valve guitar amps ). I was surprised when they appeared to do nothing at all for the switch transients.

My pictures tell the story. My DER 500 meter is very good and I have checked its accuracy with my "standards" caps I keep specifically for the purpose.
Clearly labelled 0.1 uF 275 volts AC.
They measure 3.3 pF .

Joe
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Old 4th Sep 2021, 6:26 am   #2
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Default Re: Capacitors

Well, they're obviously scrap, so an autopsy would seem to be the next step, just to satisfy curiosity.

Could the choice of component suppliers have contributed to the demise of the failed business?

I'd check all the other components before using any. And definitely destroy these so they don't ambush anyone else.

Pre-failed, non-deflagrating X2 capacitors.... whatever next?

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Old 4th Sep 2021, 8:19 am   #3
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Default Re: Capacitors

That reminds me when I used to teach Electronics at our local Technical College back in the 80s. I used to put a few duff componernts in the kits that were being built on plug in bread boards. Certainly helped with fault finding especially when a timer control had no timing.
A couple of duff 555s came in handy as well!
Of course, I was on hand to help the students learn how to fault find.
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Old 4th Sep 2021, 9:57 am   #4
Lucien Nunes
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Default Re: Capacitors

Quote:
Pre-failed, non-deflagrating X2 capacitors.... whatever next?
IIRC Sinclair achieved some commercial successes using pre-failed components. As a spectrum-owning teenager I recall feeling rather cheated when I discovered that the eight '32k x 1' ICs forming the upper 32k of RAM in a 48K machine are actually 64k x 1 dies that failed factory testing with all faults in one half. A jumper on the PCB sets the addressing to ignore the faulty half.

At the BVWTM in the 80's we had a huge bag of BY127s of which about 5% were encapsulated back to front.

But I would rather have these obvious go/no-go situations than a bazillion X2's working as series droppers in gadgets all round the shop, gradually losing value and starving their devices of power. Had one on Wednesday, phase monitoring relay in a CNC lathe. Module appeared OK because the status LED would come on at startup and stay on, and the relay would energise as the LED came on. But once the NC had booted up and the hydraulic pump came on, although the status LED stayed on solidly the relay itself glitched off. Three 220nF X2's inside the module had fallen to about 40nF and the internal +24V was browning out during the pump motor start.

We are going to see a lot more of this in the future.
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Old 4th Sep 2021, 10:17 am   #5
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Default Re: Capacitors

It sounds as if those caps are just a bad batch. Obviously they should never have got into the distribution chain, but these things happen sometimes.

Have you done some checks on the other components?
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Old 4th Sep 2021, 11:03 am   #6
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Default Re: Pre-failed Class X2 Capacitors.

If they are not fakes (they don't look like it), Tenta caps are normally very good. Seen loads in stuff I safety test and we have to confirm the safety approvals are backed up with a safety certificate.

Seems odd that so many are faulty unused. I wonder how old they are?

Mind you, I don't know that standard quoted EN 132400. The usual standard for X class and Y class caps is IEC/EN 60384 and is usually shown on the caps possibly just as 384
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Old 4th Sep 2021, 11:13 am   #7
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Default Re: Pre-failed Class X2 Capacitors.

Those half-good DRAMs (and indeed EPROMs, there was a half-good 2708 and a half-good 2716 at one time) were standard manufacturer's products, and not Sinclair selling defective parts. I guess it meant said manufacturers could sell expensive chips that would otherwise be scrap.

I can remember when a hobbyist supplier sold part-working TTL. A 7400 with 3 good gates, not 4. The problem was that often the other gates failed after a short time. I am also told that their IC tester was based on relays and uniselectors and did not test at anything like the full speed. I was caught once by one of their 'good' ICs that would not clock at anything like the specified frequency.
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Old 4th Sep 2021, 11:26 am   #8
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Default Re: Pre-failed Class X2 Capacitors.

Yeah - chuck the ambush caps out. They seem to be definitely faulty.

Back in the day, one of the things that irritated me was when someone tried to use a BNC/BNC cable and found it faulty. Then cheerfully put it back on the cable rack to waste someone else's time.

If I found one, I cut the wire in half and chucked the two halves in the bin.

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Old 4th Sep 2021, 2:59 pm   #9
stevehertz
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Default Re: Pre-failed Class X2 Capacitors.

Seems to me that X2 capacitors are more often than not the route to trouble; exploding (not doing their job) and in this case out of spec.
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Old 4th Sep 2021, 3:30 pm   #10
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Default Re: Pre-failed Class X2 Capacitors.

Back in the 1980s where I worked we ended up with a batch of 4013 CMOS chips with propagation delays of 20us or so.
Fortunately they only got fitted to boards that were used in small quantities.
They were in double sided boards.
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Old 4th Sep 2021, 10:30 pm   #11
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Default Re: Pre-failed Class X2 Capacitors.

Yes, I have checked a lot of the other components. SO FAR the caps are the first failure. I have boxes of 1000 1N4937 fast recovery diodes from Master Instrument corporation as well as 6A10 diodes from the same manufacturer. All test good and I have used quite a few upgrading some old equipment. No problems so far. Really nice "audiophool" electrolytic caps by Nichicon and Elna Cerafine, that measure superbly. IC's by the thousands that I obviously haven't checked yet, some of which I have never heard of, nor seen so many "legs" on such small bits. Resistors that to my eye look like Philips manufacture, in all the small wattages.

I will keep you posted on developments.

Joe
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Old 6th Sep 2021, 2:16 pm   #12
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Default Re: Pre-failed Class X2 Capacitors.

Foil capacitors that have been stored under adverse conditions or have a factory fault in the potting, can fail open due to oxidation. While a paper cap with faulty potting will blow up shortly after applying voltage, a foil cap will just sit there and do nothing.
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