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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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10th May 2011, 9:28 pm | #21 |
Octode
Join Date: Oct 2003
Location: Newbury, Berkshire, UK.
Posts: 1,770
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Re: Beware!
A while ago, I had this type of Rifa fail on an old Philips 'scope - The 'scope was working perfectly well, but started making a "frying" sound. While I was still scratching my head wondering about the noise, smoke poured from every available hole in the chassis. Completely filled the workshop.
IMHO, like bead tantalum caps, best avoided all together in "high energy" positions. I'll be changing any I find on sight from now on.
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Chris |
12th May 2011, 10:23 am | #22 |
Heptode
Join Date: Apr 2003
Location: Ayr, Ayrshire, UK.
Posts: 630
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Re: Beware!
I have had failures of this type of capacitor recently on three different computer power supplies dating from the mid eighties.
They go with a 'crack' and produce lots of smoke but no fuses blow and the equipment keeps running ! I will post some pictures I took when I can find them.... I think these capacitors must have a certain 'shelf life' and possibly not like temperature changes too much judging by the stress cracks I have noticed on their cases. Andy
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12th May 2011, 10:48 am | #23 |
Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
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Re: Beware!
Hi lads,
I'm pretty sure that these are the ones that live (and die) in BBC Micro PSUs. The first time one went it didn't half make me panic...since then I've had a few go and don't even bother to stop typing. Though it is worth getting up and opening a window! As far as I know they are "safe" in that I've never seen or heard of one setting fire to adjacent materials. Dom |
12th May 2011, 11:06 am | #24 |
Dekatron
Join Date: May 2006
Location: Invercargill, New Zealand
Posts: 3,440
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Re: Beware!
I've struck blown ones in a Sord M23 power supply and one of my Apple IIe's had so much smelly old capacitor goo through it's power supply I had to wash the PCB in the dishwasher twice to get most of it off! It had two blown - 0.47uF across the mains and 0.1 a little later on in the circuit.
They seem to crack, aborb moisture and fail. I replace them on sight. |
12th May 2011, 12:00 pm | #25 |
Dekatron
Join Date: Aug 2006
Location: Madrid, Spain / Wirral, UK
Posts: 7,484
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Re: Beware!
Had one fail last year in a Tandberg reel to reel series 15 motor switch. Caught it before the smoke, after noticing a strong smell and the motor randomly coming on. Definitely a type to replace on sight, file under 'old crap'!
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Regards, Ben. |
12th May 2011, 12:19 pm | #26 |
Retired Dormant Member
Join Date: Nov 2009
Location: Weardale, UK.
Posts: 1,981
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Re: Beware!
Oh well looks conclusive, 250 of them in the bin then
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12th May 2011, 2:28 pm | #27 |
Heptode
Join Date: Mar 2010
Location: Eastham, Wirral, Merseyside, UK.
Posts: 788
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Re: Beware!
HI: Chris,don't bin them,I must say the we did have some go when the RFI testing station , did on our induction hobs wacked accesive voltage in to our mains input plugs with there testing equipment and blew a couple,we also found that the mains switches where faulty and causing arcing and the caps started to overheat.
Also another problem was the soldered joints on the circuit boards were crap. After replacing said switches/soldering joints, there were no more problems. Here are some technical info for you.if you require anymore let me know.Gezza. |
12th May 2011, 2:30 pm | #28 |
Heptode
Join Date: Mar 2010
Location: Eastham, Wirral, Merseyside, UK.
Posts: 788
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Re: Beware!
more, Chris
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12th May 2011, 4:45 pm | #29 |
Retired Dormant Member
Join Date: Nov 2009
Location: Weardale, UK.
Posts: 1,981
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Re: Beware!
Wow Gezza, some great data and I do love data thanks very much I shall digest.
Chris |
12th May 2011, 6:26 pm | #30 |
Dekatron
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
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Re: Beware!
Chris!
You should change your log in to Johnny5! Hee Hee
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Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member |
12th May 2011, 10:05 pm | #31 |
Heptode
Join Date: Mar 2010
Location: Eastham, Wirral, Merseyside, UK.
Posts: 788
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Re: Beware!
Hello Johnny 5. I mean Chris.I will send you the original wall chart to go in your workshop when I'm next at the post Office as I have a spare.Gezza
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12th May 2011, 10:15 pm | #32 |
Retired Dormant Member
Join Date: Nov 2009
Location: Weardale, UK.
Posts: 1,981
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Re: Beware!
That's such a kind gesture Gezza and one which is truly appreciated.
Chris |
13th May 2011, 9:22 am | #33 |
Heptode
Join Date: Apr 2003
Location: Ayr, Ayrshire, UK.
Posts: 630
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Re: Beware!
I've attached some pictures of these Rifa's from a BBC micro PSU. The first two show the one which blew and the second two are of the 0.1uF which although not blown, was leaky.
Andy
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13th May 2011, 9:37 am | #34 |
Retired Dormant Member
Join Date: Feb 2008
Location: Auckland, New Zealand
Posts: 631
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Re: Beware!
I meet up with these little sods in commercial equipment I service. I test them at 1000 volts and if they show any leakage at all, they get changed. If the outer coating shows any crazing they are on the way out so get changed even if they pass the megger test.
Without question, potentially the most unreliable capacitor I have ever seen, apart from Hunts, Wima, TCC and UCC, and at least they had the excuse of being much older technology and made at a time when our expectations were significantly lower. Cheers Billy |
13th May 2011, 10:16 am | #35 |
Octode
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,869
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Re: Beware!
So, if I found these capacitors to be unfit for the purposes of my employer 30 years ago, how did Rifa manage to obtain all of the international certifications for this component?
It really makes you wonder about the true value of these bureaucratic test houses - I used £30 worth of test equipment and a bunsen burner. Leon. |
13th May 2011, 11:51 am | #36 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,086
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Re: Beware!
I heard that the problem of old was that these capacitors were originally specified for US 110V supplies and that when dual voltage supplies started to become more common not everyone uprated them as they looked on paper to be OK. It just meant they had a shorter life when not in the US.
I experienced a definite example of this when the filter in the Apple LISA psu went up as described. It didn't originally have a 240V supply but they upgraded it but was still essentially the same design. |
26th May 2011, 2:08 pm | #37 |
Hexode
Join Date: Aug 2007
Location: S.W. London, UK.
Posts: 416
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Re: Beware!
It was my turn last night... I was happily listening to my Revox B77 then suddenly, fizz, pop, BANG. Remarkably the mains fuse remained intact and the recorder kept on playing. As I sat in a smog filled room wondering what had just happened I was aware that couldn't hear the the tape very well due to my smoke alarm making too much noise!
Notice that the cap is also a PME271 M610 p.s. Just how long does it take for that acrid smell to go away?? Vic
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It has to be here... I've just put it down! |
26th May 2011, 5:12 pm | #38 |
Octode
Join Date: Oct 2003
Location: Newbury, Berkshire, UK.
Posts: 1,770
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Re: Beware!
Well there were traces of it in my workshop 2 days after the event
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Chris |
26th May 2011, 7:04 pm | #39 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
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Re: Beware Rifa Class X Capacitors!
About ten years ago, I had the same problem with a Sony colour set manufactured in the mid 1980's (can't remember the chassis). At the time, I was quite alarmed to find an X2 rated component fail in this way considering the stringent safety approvals for this capacitor. I think the set was that nasty one which suffered from a burn up of the main chassis due to dry joints on wirewound resistors.
I have also noticed fine cracks in the case of some Rifa class X2 capacitors so wondered whether moisture could be to blame. Symon. |
26th May 2011, 7:39 pm | #40 |
Hexode
Join Date: Mar 2005
Location: London, UK.
Posts: 318
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Re: Beware Rifa Class X Capacitors!
That does it! I had a couple of recovered PME271 capacitors in my spares store. They are now heading for landfill.
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