17 Nov
2008
17 Nov
'08
12:23 p.m.
I've taken my newly-acquired PDP-8/E apart to clean out the dust and
disintegrated foam, but I've not powered it up yet. (In fact it's still
in pieces while I sort out the foam). I'll be checking the capacitors
before I go much further.
Part of the reason for not powering it up is that it's a 110V version,
and here in the UK my mains is 240V. Looking at the engineering
drawings (on David Gesswein's site, and Highgate) for the H724 (110V)
and H724A (240V) supplies, I see transformer taps shown for both
voltages, and on the face of it, it should be very easy to convert.
Just a matter of moving the connections from tags 6 and 9 of the relay
(or "realy" as the schematic calls it :-)) Has anyone ever done this?
Another question: There are four 1N4721 rectifier diodes used for the
+8V and +15V supplies (two pairs for two full-wave rectified supplies).
Someone before me has disconnected one end of one of them. Usually
that's because it's gone short, but my meter says this one is OK. Any
ideas why?
I'm also lacking any serial interface for this machine. I do have some
other spare boards; is anyone (especially in the UK) interested in a trade?
--
Pete Peter Turnbull
Network Manager
University of York
17 Nov
17 Nov
9:12 p.m.
Pete Turnbull wrote:
I've taken my newly-acquired PDP-8/E apart to
clean out the dust and
[...]
Part of the reason for not powering it up is that
it's a 110V version,
and here in the UK my mains is 240V. Looking at the engineering
drawings (on David Gesswein's site, and Highgate) for the H724 (110V)
and H724A (240V) supplies, I see transformer taps shown for both
voltages, and on the face of it, it should be very easy to convert. Just
a matter of moving the connections from tags 6 and 9 of the relay (or
"realy" as the schematic calls it :-)) Has anyone ever done this?
If the print set shows the same part number for the transformer for both
the H724 and H724A, it will be fine. However, DEC sometimes used
transformers in 60 Hz gear that was undersized for 50 Hz, despite the
presence of appropriate taps for 240V mains. IIRC, the 120V/60Hz RX01
had this issue.
Eric
18 Nov
18 Nov
2:37 p.m.
If the print set shows the same part number for the transformer for both
the H724 and H724A, it will be fine. However, DEC sometimes used
transformers in 60 Hz gear that was undersized for 50 Hz, despite the
presence of appropriate taps for 240V mains. IIRC, the 120V/60Hz RX01
had this issue.
The RX01/RX02 PSU is somewhat strange, it uses one of those ferroresonant
transformers. So you'd have to change things depending on the mains
frequency,. I think you're right, the transformer in that unit was
different between the 50 and 60Hz versions (but the 50Hz one didn't work
properly on 60Hz mains, unlile the more normal case where the 60Hz
version is undersized for 50Hz, and the 50Hz one will work fine on 60Hz).
Of course you also had to change the drive spindle motor pulley when you
changed the mains input frequency in the RX01/02.
-tony
19 Nov
19 Nov
7:54 p.m.
On 18/11/2008 02:12, Eric Smith wrote:
Pete Turnbull wrote:
> Part of the reason for not powering it up is that it's a 110V version,
> and here in the UK my mains is 240V. Looking at the engineering
> drawings (on David Gesswein's site, and Highgate) for the H724 (110V)
> and H724A (240V) supplies, I see transformer taps shown for both
> voltages, and on the face of it, it should be very easy to convert.
If the print set shows the same part number for the
transformer for both
the H724 and H724A, it will be fine. However, DEC sometimes used
transformers in 60 Hz gear that was undersized for 50 Hz, despite the
presence of appropriate taps for 240V mains. IIRC, the 120V/60Hz RX01
had this issue.
The scan of the 240V schematic isn't very clear but it certainly looks
like the same part numbers. Anyway, I took it apart this evening and
after a bit off a tussle I managed to get at the primary terminals on
the power transformer (the small one for the relay power is easy to
see). It did indeed have both taps, labelled as per the schematic.
I've changed the mains input connections on both transformers (but not
the 115V fan connection!) so as far as I can see, it should now be ready
to go.
I've decided to be extra careful, and re-form the main electrolytics.
So far the ones I've done look fine, but it'll be a while before I get
them all done, as I have to do one at a time (more or less), and isolate
each from the circuit. The terminals are easy to get at but the wiring
is tightly packed and I can't see the values so I'm not entirely sure
which ones are which. It would help to have a component layout drawing,
which I imagine would be part of the engineering drawings set. However,
all I can find online are the schematics and layouts for the two little
control boards. Does anyone have the rest of the drawings?
--
Pete Peter Turnbull
Network Manager
University of York
20 Nov
20 Nov
10:42 a.m.
From: "Pete Turnbull" Wednesday, November 19, 2008 4:54 PM
I've decided to be extra careful, and re-form the
main electrolytics.
So far the ones I've done look fine, but it'll be a while before I get
them all done, as I have to do one at a time (more or less), and isolate
each from the circuit. The terminals are easy to get at but the wiring
is tightly packed and I can't see the values so I'm not entirely sure
which ones are which. It would help to have a component layout drawing,
which I imagine would be part of the engineering drawings set. However,
all I can find online are the schematics and layouts for the two little
control boards. Does anyone have the rest of the drawings?
From: alt.sys.pdp8 October 15, 2007
On Oct 7, 4:32 pm, "Gordon S. Hlavenka"
<nos... at crashelex.com> wrote:
The information you seek is on scan pages 10 and 14 of 35, and the PDF
is still available at crashlex.com. (I actually found it in my local
copy, then went to see if it was still out there.)
Vince
Well then, try
this:http://www.crashelex.com/pdp8e-IPB.PDF
(BTW I encourage anybody else who's archiving docs to snag this one
since I can't promise how long it'll stay on my server :-)
--
Gordon S. Hlavenka http://www.crashelectronics.com
It's bad luck to be superstitious
THANK YOU, THANK YOU,
Gordon!!
Saved me hours of tracing wires. Found 3 blown pass transistors
(2N3055) in the +5V supply. Thankfully one can still purchase these
from Digikey.
Hope to get the power supply fixed this weekend so I can start
testing boards.
Roger Wink
11:16 a.m.
On 20/11/2008 15:42, Vincent Slyngstad wrote:
From: "Pete Turnbull" Wednesday, November
19, 2008 4:54 PM
> However, all I can find online are the schematics and
> layouts for the two little control boards. Does anyone have the rest
> of the drawings?
From: alt.sys.pdp8 October 15, 2007
> On Oct 7, 4:32 pm, "Gordon S. Hlavenka" <nos... at crashelex.com>
wrote:
>> Well then, try this:http://www.crashelex.com/pdp8e-IPB.PDF
The information you seek is on scan pages 10 and 14 of
35, and the PDF
is still available at crashlex.com. (I actually found it in my local
copy, then went to see if it was still out there.)
Thanks, Vince! I actually had a local copy of that too, but I forgot,
and didn't check it. It's exactly what I want. Many thanks to Gordon,
too, for making it available.
The associated parts list also explains perfectly the discrepancy
between the part number painted on the transformer and the part number
given in the schematic.
--
Pete Peter Turnbull
Network Manager
University of York
17 Nov
17 Nov
9:13 p.m.
Hi Pete,
I'm also lacking any serial interface for this
machine. I do have some
other spare boards; is anyone (especially in the UK) interested in a trade?
I have
some serial spares.
Would trade anything for omnibus core memory!
How much core do you have?
Best wishes,
Philipp :-)
--
http://www.hachti.de
19 Nov
19 Nov
7:44 p.m.
On 18/11/2008 02:13, Philipp Hachtmann wrote:
Would trade anything for omnibus core memory!
Anything? <grin>
How much core do you have?
I've not yet tested the core, so I don't know if both sets work. I've
tested some other spare boards; one at least (an M8300) is faulty and I
may have already found a home for a couple. I'll let you know...
--
Pete Peter Turnbull
Network Manager
University of York
20 Nov
20 Nov
9:38 p.m.
New subject: PDP-8/E H724 power supply and serial interface
A few people on the list cleaned me out of my extra 8K stacks, but I still,
have 8 or 10 4K stacks. If anyone is interested please feel free to contact
me off list.
{aul
On Mon, Nov 17, 2008 at 8:13 PM, Philipp Hachtmann <hachti at hachti.de> wrote:
Hi Pete,
I'm also lacking any serial interface for this machine. I do have some
other spare boards; is anyone (especially in the
UK) interested in a trade?
I have some serial spares.
Would trade anything for omnibus core memory!
How much core do you have?
Best wishes,
Philipp :-)
--
http://www.hachti.de
5703
days inactive
5707
days old
8 comments
6 participants
participants (6)
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ard＠p850ug1.demon.co.uk -
eric＠brouhaha.com -
hachti＠hachti.de -
pete＠dunnington.plus.com -
useddec＠gmail.com -
vrs＠msn.com