Powering up a 20-year old MicroVAX II

[Roy J. Tellason]

On Sunday 01 March 2009 10:36:33 pm Brent Hilpert wrote:
> "Roy J. Tellason" wrote:
> > > If it was plugged in but not switched on and something popped, it'll be
> > > the mains filter cap.  They *do* fail, and they're easy to replace.
> >
> > In seeing photos of this in the process of dealing with it offlist,  it
> > looks exactly like that's what it was.  When I asked about the markings
> > on the failed parts I was told that they included "250V",  which is way
> > inadequate for UK mains voltages...
>
> That's not necessarily a flaw: 120/240 supplies often do the voltage
> selection by switching the circuit between bridge rectifier for 240V and
> voltage doubler for 120V. In the bridge config two caps end up in series,
> so 250V+250V=500V.

Not if the config is the two caps being across the line,  before and after the 
typical inductor that's also commonly a part of that filter...

The series connection is usually the two _main_ filter caps,  not the line 
("mains") filter components.

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