Mains transformer secondary filter cap failure

[N Cook]

100nF, 200V polyester cap across 100V secondary.
Other than internal failure to the dead short, are there any possible
scenaios that could induce such a failure?
The power amp itself seems ok, no reported problems before this failure and
no reported obvious mains problems, and no local hotspot.

 

[Sam Goldwasser]

100nF, 200V polyester cap across 100V secondary.
Other than internal failure to the dead short, are there any possible
scenaios that could induce such a failure?
The power amp itself seems ok, no reported problems before this failure and
no reported obvious mains problems, and no local hotspot.

Not really except maybe a voltage spike or old age or poor qality control....

Theoretically, I suppose a partially shorted primary could result in excessive
voltage on the secondary before a fuse blew but since it works fine, assume
it was just a random failure.

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[Tim Schwartz]

100nF, 200V polyester cap across 100V secondary.
Other than internal failure to the dead short, are there any possible
scenaios that could induce such a failure?
The power amp itself seems ok, no reported problems before this failure and
no reported obvious mains problems, and no local hotspot.

Nigel,

I've seen such a failure in one or 2 models of old NAD receivers. In
those cases, I think the capacitor just failed. I never found any other
problems with the amps.

Regards,
Tim Schwartz
Bristol Electronics

 

[N Cook]

Not really except maybe a voltage spike or old age or poor qality control....

Theoretically, I suppose a partially shorted primary could result in excessive
voltage on the secondary before a fuse blew but since it works fine, assume
it was just a random failure.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

No maker's name on the cap, its original colour and appearance, but audio
amp is only 3 years old, very expensive 350W one. Hopefully just a failure
you would normally expect to show itself before factory final test.

 

[Jitt]

100nF, 200V polyester cap across 100V secondary.
Other than internal failure to the dead short, are there any possible
scenaios that could induce such a failure?
The power amp itself seems ok, no reported problems before this failure and
no reported obvious mains problems, and no local hotspot.

Is that 100V. RMS? So about 140V Peak, 280V P-P...I'd
replace 400V, if it'll fit.

 

[Meat Plow]

100nF, 200V polyester cap across 100V secondary.
Other than internal failure to the dead short, are there any possible
scenaios that could induce such a failure?
The power amp itself seems ok, no reported problems before this failure and
no reported obvious mains problems, and no local hotspot.

How old?

 

[N Cook]

Is that 100V. RMS? So about 140V Peak, 280V P-P...I'd
replace 400V, if it'll fit.

nearer 2x55V ac so 110V RMS
The only marking is
104J
200N

no mention of ac or dc so could be 200V dc, maximum dimensions about 8x10x4
mm, I will crack open at some point.

 

[Eeyore]

100nF, 200V polyester cap across 100V secondary.
Other than internal failure to the dead short, are there any possible
scenaios that could induce such a failure?

Mains transient. I'd never use a 200V cap there.

Graham

 

[N Cook]

I expected the problem to be near the pins which are about half way along
the foils, staggered for the pin spacing.
Problem was buried in the assembly about 3/4 into the centre, a number of
sputtered/fused layers but no smoke emanation. There was localised micro
ruffling of the foil in that area whether cause or effect of localised
heating , I don't know, but the ruffling extended the width of the foil, not
just the small "spot weld" area.