30 Aug
2019
30 Aug
'19
10:27 p.m.
On Aug 28, 2019, at 2:07 AM, Guy Dunphy via cctalk
<cctalk at classiccmp.org> wrote:
An extremely common problem with all old electronics from around that era.
The mains filter caps are commonly 'RIFA' brand metalized polyester film,
encapsulated in a clear-honey-coloured resin.
The problem is that the resin embrittles and shrinks with age, resulting in
many small cracks. (And sometimes large pieces falling off.)
The cracks let in moisture, which absorbs into the insulating film.
I suspect those notorious Rifa brand capacitors would not be so problematic if they had
polyester film dielectric. But if I'm not mistaken, they don't; they have *paper*
dielectric!
Aside from that one correction, I agree with everything else you wrote about the likely
failure mechanism of these evil little rectangles of compressed smoke and fire.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/