1 Mar
2009
1 Mar
'09
5:54 p.m.
On Sat, 2009-02-28 at 14:23 +0000, Robert Jarratt wrote:
Some have suggested it blew because I had insufficient
load. I had a TK50
and an RD53 attached, would that no be sufficient. Furthermore I did not
actually switch the PSU on, just connected it to the mains, would the load
connected to the PSU matter when the PSU is not actually switched on?
I'd use a "modern" old hard disk, not one that's likely to be useful.
Or a couple of car indicator bulbs.
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.
There was also a suggestion that the PSU would have
needed switching
separately for 50Hz operation as well. The hardware manual I have for the
machine tells me how to switch between 110 and 240, but does not say
anything about switching it for frequency, so I suspect this was not an
issue here.
It won't have a 50/60Hz switch, just voltage.
Gordon
1 Mar
1 Mar
7:11 p.m.
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...
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
7:36 p.m.
"Roy J. Tellason" wrote:
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.
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...
7:53 p.m.
On Sunday 01 March 2009 10:36:33 pm Brent Hilpert wrote:
"Roy J. Tellason" wrote:
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.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
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...
9:25 p.m.
"Roy J. Tellason" wrote:
On Sunday 01 March 2009 10:36:33 pm Brent Hilpert wrote:
OK, (you've seen the photos), I thought the ealier poster might be alluding
back to the electroytics discussion, so just threw in the comment.
"Roy J. Tellason" wrote:
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. 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... 
2 Mar
2 Mar
10:50 a.m.
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
6 Mar
6 Mar
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
2 Mar
2 Mar
10:48 a.m.
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...
Not necessarily. Some mains filter capacitors used over here are rated at
250VAC working. In other words they are designed to work on 250V (or
less) AC mains.The DC rating is a lot higher.
There are also several 'classes' of mains filter capacitors (X2, Y2,
etc). One of them (I forget which, but I would check before replacing
anything) is designed so it can't fail short-circuit. That is the type to
use between either side of the mains and the case/dafety earth. The one
across the mains is less critical safety-wise.
-tony
5773
days inactive
5777
days old
7 comments
5 participants
participants (5)
-
ard＠p850ug1.demon.co.uk -
gordonjcp＠gjcp.net -
hilpert＠cs.ubc.ca -
robert.jarratt＠ntlworld.com -
rtellason＠verizon.net