Subject: PDP-11/34A / BA11-K PSU

From: Jochen Kunz <[email-masked]>
Date: Thu May 22 13:20:01 2003

Hi. 

I got some more parts of that disassembled PDP-11/34A yesterday. I think
I have now all PSU parts:
- power inlet unit with mains cable, circuit breaker ... and a PCB that
looks like a small PSU.
- one big transformer
- one small transformer
- one H785 battery backup regulator module
- one H745 -15 PSU module
- two H7441 +5V PSU modules 
- a PCB that is labled "BATTERY CHARGER"
- a bag full of screws

Some time ago I got the front half of the BA11-K, i.e. a card cage with
the system units, all UniBus cards, power distribution panel and front
panel.

Obviously missing: 
- back of the BA11-K where the PSU bricks, transformers, ... are mounted
- fans
- bulkheads for the console serial line, the serial multiplexer, RK07,
...
- UniBus extender and terminator. [1] 

I got the card cage, power distribution panel, system units and all
UniBus cards in one piece, but disassembled it to clean it. I know how
to remount that, but I have no clue how all the PSU parts fit togeter
and if there are some parts missing I didn't list above. It would be
nice if someone who knows this machine could give me some hints...

I was toled that one of the PSU bricks is broken. I found some manuals
on http://www.mainecoon.com/classiccmp/PDP-11-34A/ but I can't read
those TIFFs. I tried with xv, gimp, tiff2ps, Netscape 4.7x, Mozilla 1.2.
I took the CDR with the TIFFs with me to work and tried to view them on
a WinXP machine (puke). The machine nearly crashed when I tried to open
the files. My SGI Indogo2 is broken so I can not try some IRIX tools.
Where else can I get some schematics of the PSU bricks in a readable
form? 

[1] There is an other, smaler BA11 with a custom UniBus interface from
Linotype for some photo typesetting machinery... I have the M9312
bootstrap terminator for the "beginning" of the bus where the CPU
resides. 
-- 

tschüß,
       Jochen, who is now heating the soldering iron for the Indogo2...

Homepage: http://www.unixag-kl.fh-kl.de/~jkunz/

---

From: "Antonio Carlini" <[email-masked]>
Date: Thu May 22 13:47:00 2003

> I was toled that one of the PSU bricks is broken. I found 
> some manuals on 
> http://www.mainecoon.com/classiccmp/PDP-11-> 34A/ but I can't 
> read those TIFFs. I tried with xv, gimp, 
> tiff2ps, Netscape 4.7x, Mozilla 1.2. I took the CDR with the 
> TIFFs with me to work and tried to view them on a WinXP 
> machine (puke). The machine nearly crashed when I tried to 
> open the files. My SGI Indogo2 is broken so I can not try 
> some IRIX tools. Where else can I get some schematics of the 
> PSU bricks in a readable form? 

Try IrfanView - I think that's what I used. If that
fails, I can probably turn them into pdfs 
(and convert to g4 along the way). As long as you
can read the various large scanned pdfs on the 
web (like, say, the VAX-11/750 schematics), this 
should work for you.

Antonio
 
-- 

---------------
Antonio Carlini             [email-masked]

---

From: [email-masked] (Tony Duell)
Date: Thu May 22 15:24:00 2003

> Hi.=20
> I have now all PSU parts

If that's a PCB that covers the top side of that module, then it is a 
small PSU (+15V at a few amps, and also the ACLO, DCLO, LTC signals). 
There should also be a little PCB inside the module which controls the 
mains relay, I think.

> - one big transformer

OK

> - one small transformer

I don't remember there being a second transformer inside the BA11-K. Is 
this possibly part of the battery backup option (to go with the charger 
PCB below -- this doesn't fit inside the BA11-K)

> - two H7441 +5V PSU modules=20

OK -- that should be enough to run the machine. You don't _need_ the 
battery backup unit, BTW...

> - a PCB that is labled "BATTERY CHARGER"

AFAIK the battery backup unit was a separate box that contained the 
batteries, the charger PCB, and probably the small transformer.

> Obviously missing:=20
> - UniBus extender and terminator. [1]=20
> 

YOu really need the printset. The bricks connect to the 8 pin mate-n-lock
plugs wired to the distribution PCB (but you must get them in the right
places!), then there's a little cable that connectes between the +15V PSU
and the distribution PCB. The transformer connects to that cable, to the 8
pin mate-n-lock on the distribution PCB and to the 4 pin connector on the
front of the power controller. THe power switch wiring from the front of
the cabinet connects to one of the 3 pin connectors on the power 
controller. The fans connect to the primary side of the transformer, BTW.

> and if there are some parts missing I didn't list above. It would be

Maybe the odd cable or connector is missing, but you have the main parts.

-tony

---

From: Jochen Kunz <[email-masked]>
Date: Fri May 23 03:27:01 2003

On 2003.05.22 22:18 Tony Duell wrote:

> > - power inlet unit with mains cable, circuit breaker ... and a PCB
> > that looks like a small PSU.
> If that's a PCB that covers the top side of that module,
Yes.

> There should also be a little PCB inside the module which controls the
Yes.

> > - one small transformer
> I don't remember there being a second transformer inside the BA11-K.
> Is this possibly part of the battery backup option (to go with the
> charger PCB below -- this doesn't fit inside the BA11-K)
It looks like this. The samll transformer has its own mains cable. 

> battery backup unit, BTW...
Very good. Now I need better weather. I have to sand-blast and repaint
the card cage (rust everywhere). I will not do this inside the house...

> YOu really need the printset.
Meanwhile I got the tiffs in a readable form by using tiffsplit. I will
have a look at them and print the important ones. 

> Maybe the odd cable or connector is missing, but you have the main
Souns good. When I get the H745 and H7441 PSU bricks working I will try
to build a minimal setup to see if the CPU and RAM is alive. Then add
the peripheral controllers ... Unfortunately SMPSUs are not my friends. 

And if the machine works there is the next task: Rebuild the rusty RK07.
-- 

tschüß,
       Jochen

---

From: Jochen Kunz <[email-masked]>
Date: Fri May 23 03:30:09 2003

On 2003.05.22 20:43 Antonio Carlini wrote:

> Try IrfanView - I think that's what I used. 
Is that some M$-WinWare? (I own only one PeeCee, a IBM PS/2-80 386/20.)

Hmmm. Several people reported the the files are readable. So there must
be a way...
[playing around with the tiff tools]
Ahhh, now it works. I had to split the multi-page tiffs into individual
tiff files and now I can view them. xv still crashes when I load
multiple files and press the "Next" button but I can get somthing on the
screen. 
-- 

tschüß,
       Jochen

---

From: [email-masked] (Tony Duell)
Date: Sat May 24 16:47:00 2003

> > If that's a PCB that covers the top side of that module,

Do you have a cable with a white (nylon?) edge connector to fit onto the 
front edge of this PCB? If not, you need to make one.

> the peripheral controllers ... Unfortunately SMPSUs are not my friends.=20

Actually, these bricks are relatively friendly in that there are no 
lethal voltages in them (they runn form a 20-30V AC input, which comes 
from the big transformer and is isolated from the mains). The maximum 
current that will flow in the event of a short circuit is not that high 
either (10's of amps), although it is enough to make small signal 
transistors explode (that's from experience!).

> And if the machine works there is the next task: Rebuild the rusty RK07.

I bought an RK07 that was full of water (seriously, it poured out of the 
hollow baseplate...). After drying it out, cleaning the heads, 
connectors, etc, it worked fine...

-tony

---

From: Jochen Kunz <[email-masked]>
Date: Sun May 25 04:58:00 2003

On 2003.05.23 16:08 Tony Duell wrote:

> Do you have a cable with a white (nylon?) edge connector to fit onto
> the front edge of this PCB? If not, you need to make one.
Hmmm. I think there was a smal cable in the bag with the screws. 
> lethal voltages in them
[...]
Yes, but I have no clue about SMPSUs and there theory of operation. All 
I know is that they switch the primary power on and off to pump some 
energy to the secondary side. I have some local friends who know how 
this things work, so I am in the hope to get some help. 
> although it is enough to make small signal
That reminds me of an LED that lost its "head"... ;-) 
> I bought an RK07 that was full of water (seriously, it poured
> out of the hollow baseplate...). After drying it out, cleaning
> the heads, connectors, etc, it worked fine...
When I unmounted the fan, I took it over to the waste basket, turned it 
around and a "waterfall" of rust came out of it. I sand-blasted it 
meanwhile. The air filter is unusable and full of dirt. But the heads 
and voice coil look good so I am in good hope.
-- 

tschüß,
           Jochen

Homepage: http://www.unixag-kl.fh-kl.de/~jkunz

---

From: [email-masked] (Tony Duell)
Date: Sun May 25 16:11:37 2003

> Hmmm. I think there was a smal cable in the bag with the screws.=20

IF you're missing this, it's not too hard to make it...

> Yes, but I have no clue about SMPSUs and there theory of operation. All=20

Well, you may not need to really understand what you are doing at first. 
About 95% of problems in these bricks are cured by testing and replacing 
the power transsitors and the electrolytic capacitors.

-tony

---

From: Jochen Kunz <[email-masked]>
Date: Mon May 26 03:01:01 2003

> IF you're missing this, it's not too hard to make it...
I am back at home so I could look: I have the cable. 

> > Yes, but I have no clue about SMPSUs and there theory of operation.
> Well, you may not need to really understand what you are doing at
> first. About 95% of problems in these bricks are cured by testing 
> and replacing the power transsitors and the electrolytic capacitors.
Well. I am an engineer. I want to understand and analyze, not blind
poking. 

OK. It looks like I need some off time from my NetBSD hacking project so
I will try to set up the transformer, bricks, etc. on my workbench to
have a closer look. My multimeter and my HP scope are my friends. ;-) 
-- 

tschüß,
       Jochen

---

From: [email-masked] (Tony Duell)
Date: Mon May 26 17:30:45 2003

> > first. About 95% of problems in these bricks are cured by testing=20
> poking.=20

OK... That's good. I hate lucky-dip servicing too... There are several 
good references on SMPSU design (the section in 'The Art of 
Electronics' 2nd edition is a good staring point), and these DEC PSU 
bricks are a pretty standard step-down regualtor circuit. The only 
unconvention feature is that the controller is a 723 chip, not a special 
SMPSU chip. The 723 is basically a votlag reference and a (separate) 
op-amp in one package, so it's not hard to understand.

  o-----\     /----------------+-----UUUUUUUUUUUU-------+-------o
         \  </                 |         L              |
        --------               |                        |
Im         |                 -----                    =====
       Control                 ^  D                   ----- C   Out
                              /|\                       |
                               |                        | 
                               |                        |
  o----------------------------+------------------------+-------o

Here's the basic circuit of the power-handling part of the step-down 
regulator. When the control signal is asseted, and the transistor is 
turned on, D is reverse-biased (so does nothing), and the left terminal 
of L is +ve. Current starts to flwo through L, but the back emf of L 
effectively drops the voltage that appears at the load (and, indeed, 
energy is stored in the magnetic field of L). When the control signal is 
deasserted, the transistor turns off. The magnetic field of L collapses, 
so that now the left terminal is -ve. A current (effectively supplied by 
L) no flows via D (the 'flywheel diode'), and supplies the load. C, of 
course, acts as an output smoothing capacitor and preveents the load 
voltage changing too much.

Yes, that's an oversimplification (but not as bad as some explanations 
I've seen in print) but it will at least explain what the main components 
on the schematic do.

-tony

---

From: Andreas Freiherr <[email-masked]>
Date: Tue May 27 09:21:00 2003

Jochen,

>>- two H7441 +5V PSU modules

the latter are 32A regulators, right? - If so, and particularly if part 
of the box is from a different source, you may want to make sure you 
have the later revision of the power distribution gear.

The older version might let out some magic smoke: it was designed for 
the (IIRC) H744 brick (25A max.). When the old distribution is used with 
the later, stronger H7441, and with a stuffed backplane, it can get 
overloaded. I may be able to look up the critical part numbers if you 
cannot find them elsewhere.

--
Andreas Freiherr
Vishay Semiconductor GmbH, Heilbronn, Germany
http://www.vishay.com

---

From: Jochen Kunz <[email-masked]>
Date: Tue May 27 13:03:00 2003

On 2003.05.27 16:16 Andreas Freiherr wrote:

> the latter are 32A regulators, right? 
Yes.

> If so, and particularly if part 
> of the box is from a different source, 
I am sure that all parts come from the same machine. The previous owner
disassembled it in the attempt to repair it. He faild and stored the
parts in his garage some years ago. He is cleening up this garage during
the past months and every time he comes acros a PDP-11 part he pushes it
in my direction... 
-- 

tschüß,
       Jochen

---

From: Jochen Kunz <[email-masked]>
Date: Tue May 27 17:19:01 2003

On 2003.05.26 23:47 Tony Duell wrote:

> There are several good references on SMPSU design 
I should feed google... ;-) 

> (the section in 'The Art of 
> Electronics' 2nd edition is a good staring point), 
Unfortunately I don't own this book. When I tried to order it from .de,
the cost was prohibitive. 

> and these DEC PSU 
> bricks are a pretty standard step-down regualtor circuit.
Well, it looks like the H7441 has some funky design tricks. 

> The only unconvention feature is that the controller is 
> a 723 chip, not a special SMPSU chip. 
The H745 has a 723, the H7441 has two OPAs and two NE555. The H745 looks
quite simple and I think I understand what the different parts do, but
the H7441??? One OPA seams to do some over current protection, one the
voltage regulation. So the NE555 are doing the ON / OFF timing??? Have
to dig deeper into that... 

Unfortunately it doesn't seam as simple as the SGI Indigo2 PSU repair I
did today. I had a close look at the PCBs of the PSU and saw
electrolyte... The machine seams to run stable again, now that I
replaced the electrolyte capacitor in question. :-) 
-- 

tschüß,
       Jochen

---

From: [email-masked] (Tony Duell)
Date: Tue May 27 18:09:00 2003

> > (the section in 'The Art of=20
> > Electronics' 2nd edition is a good staring point),=20
> the cost was prohibitive.=20

It's not cheap in the UK (about \pounds 40, I think), but it is _good_. I 
think it's worth the money. Of course I don't know what price you were 
quoted...

> > and these DEC PSU=20
> Well, it looks like the H7441 has some funky design tricks.=20

Oh, the H7441. For some reason I assumed you had standard H744 5V 25A 
regulators. Those also use the 723.

> 
> > The only unconvention feature is that the controller is=20
> > a 723 chip, not a special SMPSU chip.=20
> to dig deeper into that...=20

Probably one 555 is an oscillator, the other is the pulse-width modulator 
or something. I don't have the H7441 printset to hand. But to be honest, 
problems with the control circuitry are very uncommon in these bricks 
(and indeed in SMPSUs in general) -- most of the problems are in the 
power-handling part.

> electrolyte... The machine seams to run stable again, now that I

As I said, most SMPSU faults are capacitors or power transistors :-)

> replaced the electrolyte capacitor in question. :-)=20

-tony

---

From: Brian Chase <[email-masked]>
Date: Tue May 27 22:03:00 2003

> the cost was prohibitive.

It's 65 EUR through Amazon--worth the price IMHO.

   <http://www.amazon.de/exec/obidos/ASIN/0521370957>

-brian.

---

From: Jochen Kunz <[email-masked]>
Date: Wed May 28 09:10:00 2003

On 2003.05.28 01:03 Tony Duell wrote:

> It's not cheap in the UK (about \pounds 40, I think), but it is
> _good_. I think it's worth the money.
> Of course I don't know what price you were
I have no problem to pay good money for a good book. But 250,-DM
(~130,-EUR) was to much. (Book store at the local university. They
needed to make a special order...) I tried amazon, but they cold not
deliver this book to Germany back then. This may have changed. (Have to
check Brians hint...) 

> As I said, most SMPSU faults are capacitors or power transistors :-)
One problem is obvious: The big 24000 uF capacitor is missing from one
brick and this brick was repaird bevore. There are some burned traces on
the PCB that where replaced with wire and solder long ago. Unfortunately
it looks like I will not get time for the PDP-11 this evening too. Some
local computer colectors are making a barbecue. :-) 
-- 

tschüß,
       Jochen

---

From: [email-masked] (Tony Duell)
Date: Fri May 30 17:35:59 2003

> One problem is obvious: The big 24000 uF capacitor is missing from one

The value of that capacitor is not _too_ critical. 22000uF would be near 
enough, for exampkle.

> local computer colectors are making a barbecue. :-)=20

You are lucky to have other local collectors.

-tony

---

From: Jochen Kunz <[email-masked]>
Date: Sat May 31 03:30:01 2003

On 2003.05.31 00:06 Tony Duell wrote:

> The value of that capacitor is not _too_ critical. 22000uF would be
> near enough, for exampkle.
Sure. The bigest problem would be to find one that fits physically into
the brick. I haven't checked this yet.

> You are lucky to have other local collectors.
Yes. There is the sun3zoo... an other collector who is that bussy
shuffling around machines that he never gets time to get them running
and there is David who takes _everything_ that looks like a computer.
(Got the 11/34A from him.) 
-- 

tschüß,
       Jochen

---

From: [email-masked] (Tony Duell)
Date: Sat May 31 13:11:43 2003

> the brick. I haven't checked this yet.

The good news is that capacitors have got smaller over the years, so a 
modern one is likely to be able to fit in the case. You might have to 
make up some brackets, etc to hold it there...

> (Got the 11/34A from him.)=20

You are lucky. I don;t know of any others in the SW London area, or even 
in all of London. Pity, it would be nice to meet some from time to time...

-tony