6 Mar
2009
6 Mar
'09
3:26 p.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: 02 March 2009 18:51
To: cctalk at classiccmp.org
Subject: Re: Powering up a 20-year old MicroVAX II
In sending Roy the information on the markings I omitted what looks like a
"~" after the 250V marking (the casing fragment is damaged in that area), so
the caps are probably rated for 250V AC. I can also see an X2 marking on one
of the caps (the other one is too damaged to see). As the damage is indeed
to two caps on the mains filter, I have purchased replacements which I will
be fitting this weekend.
The rest of the PSU *appears* to be in good condition but I do not have
anything to test ESR with and I do not have a variac or the knowledge of how
to use one, so I am unsure whether I should attempt to connect the PSU to
the mains again or whether I should attempt to switch it on. If I do feel
brave I will only connect a load that I do not care too much about.
I will worry about the harness later, but know that I need to fix this too
eventually.
Regards
Rob
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.
For the mains smoothing capacitors (large electrolytics after the
rectifier stage), sure. But for the mains filter capacitors
(non-polarised, connected acrsso the mains or between one side of the
mains and ground, before the bridge rectifer), I doubt it.
-tony