VT100 PSU smelling.

tony duell ard at p850ug1.demon.co.uk
Sat Jan 23 12:01:16 CST 2016

> It's a well-known fault, but has anyone ever known one fail and actually
> cause any damage (other than to itself)? AIUI, they're there to reduce

Not really. Maybe a blown fuse. I have had the live-earth capacitor in a filter 
fail and trip the RCD in my consumer unit (meaning I was in the dark until I 
reset t). Does damage to my nerves count :-)

If one of these capacitors in a mains filter circuit fails I tend to replace the
lot (for all  I don't like shotgun debugging). If I was repairing something for
somebody else then I'd probably change them [1]). I might change them if I
was rebulding the PSU section of a machine I own. Otherwise I just leave them
until the fail.

[1] Otherwise when they fail a few weeks/months/years later I might find I have
to replace them for free. 

Incidentally, some machines have those sealed metal cans containing filter
capacitors, inductors and sometimes discharge resistors [2]. Has anyone ever
had the capacitors in one of those fail?

[2] I wish the manufacturers would print a schematic on the can, or at least in
an available data sheet. If I measure a 1M leak to earth from the live pin (say),
I want to know if it's a deliberate discharging resistor or a leaking capacitor.


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