1 Jun
2021
1 Jun
'21
1:16 p.m.
After a few years in storage I'm finally getting to play with my PDP-11
stuff again. Figured I'd start small so rolled out the 11/23. PSU looks
fine, pulled all the cards and checked voltages, no problem. Shortly after
however, some magic smoke was released from the block in the back where AC
comes in and the power switch is mounted. The only other thing in there is
a big old line filter. Judging by the smell, I suspect a filter capacitor
has given up the ghost. I'd check, but the whole thing is soldered shut so
not exactly easily serviceable. Would I be correct in thinking such filters
aren't entirely necessary and could just be bypassed? It looks like the
manufacturer (JMK) is still going so a new replacement might not be out of
the question. Whether I could find one with the same mounting holes etc. is
another question I've not looked into yet.
Cheers,
Steve
1 Jun
1 Jun
1:38 p.m.
On Jun 1, 2021, at 4:16 PM, Steve Maddison via cctalk
<cctalk at classiccmp.org> wrote:
After a few years in storage I'm finally getting to play with my PDP-11
stuff again. Figured I'd start small so rolled out the 11/23. PSU looks
fine, pulled all the cards and checked voltages, no problem. Shortly after
however, some magic smoke was released from the block in the back where AC
comes in and the power switch is mounted. The only other thing in there is
a big old line filter. Judging by the smell, I suspect a filter capacitor
has given up the ghost. I'd check, but the whole thing is soldered shut so
not exactly easily serviceable. Would I be correct in thinking such filters
aren't entirely necessary and could just be bypassed? It looks like the
manufacturer (JMK) is still going so a new replacement might not be out of
the question. Whether I could find one with the same mounting holes etc. is
another question I've not looked into yet.
I'm not sure if you're talking about the same sort of device I had trouble with,
so FYI: the Pro power supply is a box the size of an old-fashioned Bible, with a CEE power
inlet at one end. That inlet is actually part of a sealed metal box containing a power
filter.
Mine decided to let out its magic smoke, in quite spectacular fashion, stinking up the
workshop and leaking evil looking black tarry stuff over the insides of the power supply.
But the supply appeared to be intact in other respects.
I couldn't find a matching filter, so instead I found a functionaly similar filter
that's physically smaller. I then created an adapter plate with a hole to accept the
new filter, and a flange sized to match the old one. My sheet metal skills aren't
great so it doesn't look all that professional but it's plenty good to get the job
done.
FYI, the new filter is this one:
https://www.digikey.com/en/products/detail/schurter-inc/5120.2006.0/1843934 -- about half
the size of the one it replaces.
paul
2 Jun
2 Jun
3:34 a.m.
On Tue, 1 Jun 2021 at 22:38, Paul Koning <paulkoning at comcast.net> wrote:
I'm not sure if you're talking about the same sort of device I had trouble with,
so FYI: the Pro power supply is a box the size of an old-fashioned Bible, with a CEE power
inlet at one end. That inlet is actually part of a sealed metal box containing a power
filter.
Mine decided to let out its magic smoke, in quite spectacular fashion, stinking up the
workshop and leaking evil looking black tarry stuff over the insides of the power supply.
But the supply appeared to be intact in other respects.
I couldn't find a matching filter, so instead I found a functionaly similar filter
that's physically smaller. I then created an adapter plate with a hole to accept the
new filter, and a flange sized to match the old one. My sheet metal skills aren't
great so it doesn't look all that professional but it's plenty good to get the job
done.
FYI, the new filter is this one:
https://www.digikey.com/en/products/detail/schurter-inc/5120.2006.0/1843934 -- about half
the size of the one it replaces.
Yeah, I think we're talking about the same thing although mine looks
to be significantly larger than your replacement, measuring about
120x75x45mm. From what I've read they are both sealed/soldered and
potted so that would explain the black goo. Fortunately mine didn't
quite get to that stage although it was suitably "fragrant" for sure.
I will double check the specs but your replacement looks like it'd
work for me too - very kind of them to put the schematic on the
outside :) Thanks for the link!
-Steve
6:11 a.m.
On Jun 2, 2021, at 6:34 AM, Steve Maddison via cctalk
<cctalk at classiccmp.org> wrote:
On Tue, 1 Jun 2021 at 22:38, Paul Koning <paulkoning at comcast.net> wrote:
You're welcome. There are plenty of other filters similar to the one I mentioned; it
just happens that this one was a good replacement for the one that failed in my system.
For that matter, there are a number of other suppliers. If you prefer screw mount rather
than snap-in, that's available. Integrated switches and/or fuse holders I assume are
there as well, I didn't look. Also various filter configurations and current
ratings.
paul
I'm not sure if you're talking about the same sort of device I had trouble with,
so FYI: the Pro power supply is a box the size of an old-fashioned Bible, with a CEE power
inlet at one end. That inlet is actually part of a sealed metal box containing a power
filter.
Mine decided to let out its magic smoke, in quite spectacular fashion, stinking up the
workshop and leaking evil looking black tarry stuff over the insides of the power supply.
But the supply appeared to be intact in other respects.
I couldn't find a matching filter, so instead I found a functionaly similar filter
that's physically smaller. I then created an adapter plate with a hole to accept the
new filter, and a flange sized to match the old one. My sheet metal skills aren't
great so it doesn't look all that professional but it's plenty good to get the job
done.
FYI, the new filter is this one:
https://www.digikey.com/en/products/detail/schurter-inc/5120.2006.0/1843934 -- about half
the size of the one it replaces.
Yeah, I think we're talking about the same thing although mine looks
to be significantly larger than your replacement, measuring about
120x75x45mm. From what I've read they are both sealed/soldered and
potted so that would explain the black goo. Fortunately mine didn't
quite get to that stage although it was suitably "fragrant" for sure.
I will double check the specs but your replacement looks like it'd
work for me too - very kind of them to put the schematic on the
outside :) Thanks for the link!
-Steve 
1 Jun
1 Jun
2:39 p.m.
Interesting: I just tried firing up a pair of BA11-N's to see if they
work. One blew the fuse in that block in the back and I thought it was a
shorted PS but the PS input caps are not shorted. I'll check to see if
the filter capacitor in that spot is shot.
On 6/1/2021 4:16 PM, Steve Maddison via cctalk wrote:
After a few years in storage I'm finally getting
to play with my PDP-11
stuff again. Figured I'd start small so rolled out the 11/23. PSU looks
fine, pulled all the cards and checked voltages, no problem. Shortly after
however, some magic smoke was released from the block in the back where AC
comes in and the power switch is mounted. The only other thing in there is
a big old line filter. Judging by the smell, I suspect a filter capacitor
has given up the ghost. I'd check, but the whole thing is soldered shut so
not exactly easily serviceable. Would I be correct in thinking such filters
aren't entirely necessary and could just be bypassed? It looks like the
manufacturer (JMK) is still going so a new replacement might not be out of
the question. Whether I could find one with the same mounting holes etc. is
another question I've not looked into yet.
Cheers,
Steve
2 Jun
2 Jun
3:48 a.m.
On Tue, 1 Jun 2021 at 23:39, Chris Zach via cctalk
<cctalk at classiccmp.org> wrote:
Interesting: I just tried firing up a pair of BA11-N's to see if they
work. One blew the fuse in that block in the back and I thought it was a
shorted PS but the PS input caps are not shorted. I'll check to see if
the filter capacitor in that spot is shot.
That is also interesting to me, that you have a fuse in there or even
any visible components other than switches. Maybe they opted for more
discrete components in other variations of the chassis (I can't
actually find the BA11 designation on mine). My actual PSU also seems
to be unscathed although I have not checked it thoroughly as yet.
-Steve
6:13 a.m.
Really? There is a 10a fuse in a round holder on the back of the rack,
right by the plug input. Swapping the H786 power supply with another one
results in a working unit for me, so I don't think the problem is in the
power switch box.
Maybe you have a BA11-M? Is it a 4 slot chassis or 9?
C
On 6/2/2021 6:48 AM, Steve Maddison via cctalk wrote:
On Tue, 1 Jun 2021 at 23:39, Chris Zach via cctalk
<cctalk at classiccmp.org> wrote:
Interesting: I just tried firing up a pair of BA11-N's to see if they
work. One blew the fuse in that block in the back and I thought it was a
shorted PS but the PS input caps are not shorted. I'll check to see if
the filter capacitor in that spot is shot.
That is also interesting to me, that you have a fuse in there or even
any visible components other than switches. Maybe they opted for more
discrete components in other variations of the chassis (I can't
actually find the BA11 designation on mine). My actual PSU also seems
to be unscathed although I have not checked it thoroughly as yet.
-Steve
7:06 a.m.
On Wed, 2 Jun 2021 at 15:13, Chris Zach via cctalk
<cctalk at classiccmp.org> wrote:
Really? There is a 10a fuse in a round holder on the back of the rack,
right by the plug input. Swapping the H786 power supply with another one
results in a working unit for me, so I don't think the problem is in the
power switch box.
Maybe you have a BA11-M? Is it a 4 slot chassis or 9?
According to my old notes it's a BA11-SB, so 9 slot with H7861 power
supply. The block at the back has part number H403-B, no fuse holder,
just the main on/off switch and another switch held in place by a
plastic plate. Based on the inscriptions on said plate, I'm guessing
the latter to select the required line voltage.
-Steve
4:35 a.m.
Those filter caps also cause other problems. I had now two cases in
succession where an old computer tripped the Residual Current Device (RCD)
in my switchboard. Both used Sprague 0.1 uF filter caps in "bathtub"
configuration in a metal can. Each cap is connected on one side to ground
and the other side is connected to active and neutral respectively. These
leak more than the 30 mA tolerated by my RCD which is compulsory in all
mains switchboards in Western Australia. I think that the capacitors are
not actually faulty but 0.1 uF is simply too large. The filter design
predates RCDs. There are "proper" mains filters which don't exhibit this
problem with RCDs, but of course they mechanically won't fit where the old
filter caps were.
Best regards
Tom Hunter
On Wed, Jun 2, 2021 at 4:17 AM Steve Maddison via cctalk <
cctalk at classiccmp.org> wrote:
After a few years in storage I'm finally getting
to play with my PDP-11
stuff again. Figured I'd start small so rolled out the 11/23. PSU looks
fine, pulled all the cards and checked voltages, no problem. Shortly after
however, some magic smoke was released from the block in the back where AC
comes in and the power switch is mounted. The only other thing in there is
a big old line filter. Judging by the smell, I suspect a filter capacitor
has given up the ghost. I'd check, but the whole thing is soldered shut so
not exactly easily serviceable. Would I be correct in thinking such filters
aren't entirely necessary and could just be bypassed? It looks like the
manufacturer (JMK) is still going so a new replacement might not be out of
the question. Whether I could find one with the same mounting holes etc. is
another question I've not looked into yet.
Cheers,
Steve
1072
days inactive
1073
days old
8 comments
4 participants
participants (4)
-
ccth6600＠gmail.com -
cz＠alembic.crystel.com -
paulkoning＠comcast.net -
steve＠cosam.org