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 Another Mains Cap Explodes.
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 Return to top of page · Post #: 1 · Written at 3:34:37 PM on 20 April 2024.
Labrat's avatar
 Location: Penrith, NSW
 Member since 7 April 2012
 Member #: 1128
 Postcount: 381

Hi fellow vintage electronics nuts. I was working on an old transistor radio a few days ago, when the mains suppression caps in the power supply I was using failed dramatically.

Failing mains filter caps are becoming far, far too common. I am getting shell shock from the frequent explosions. It is quite unnerving when you are very close to the site of the action. In this latest failure, the caps in the panel mount, I.E.C. mains input plug/filter assembly suddenly let go, and filled the room with acrid smoke. Although the filter was enclosed in metal it managed to vent rather than explode.

Not a cap from 1975 this time, but one from week fifty of 1997. Being part of a bench power supply and not a television, it would have had almost zero hours of operation when compared to a television. Personally, I will never again power an old piece of equipment without first replacing or removing the mains caps.

The irony, this type of socket was not needed in this product. The mains fed directly into a mains transformer.
I replaced it with a non-explosive type.

Stay safe and wear a flack jacket.

Photo sent to Brad.


IEC socket
IEC socket

 Return to top of page · Post #: 2 · Written at 5:05:07 PM on 20 April 2024.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2405

Just because it feeds into a mains transformer does not make the mains filter redundant, as anyone who has put a product through compliance testing will tell you.

An ordinary mains transformer feeding a bridge into a filter cap generates harmonics back down the mains line. There is a particularly nasty harmonic at 455kHz. But the rubbish extends up to beyond 30MHz without a mains filter.

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