Digital Equipment Corporation PDP-11/04 & PDP-11/34 Minicomputers - Teardown

[intabits]

I've had these two machines for many years, and I've been very naughty, because I've done nothing with them. They've just been sitting in my "museum room", collecting dust.




So it's time to do something about that, clean them up and get them operating, at least as standalone units that can be operated via the front panel.
First up, have a look inside, note what's there and make a video.

The card cages.  11/34 at top, 11/04 at bottom:-




A selection of the boards. Power supply covers removed:-




Teardown video:-




Links to some of the many documents available on BitSavers:-

PDP11/34:-
http://bitsavers.trailing-edge.com/pdf/dec/pdp11/1134/

PD11/04:-
http://bitsavers.trailing-edge.com/pdf/dec/pdp11/1104/

PDP11 general:-
http://bitsavers.trailing-edge.com/pdf/dec/pdp11/

Power supply:-
http://bitsavers.trailing-edge.com/pdf/dec/unibus/EK-BA11L-TM-001_Oct77.pdf


The next step will be to check/fix the power supplies. Coming soon...

[LapTop006]

Neat!

Getting an 11 to have a "real" UNIX machine is on my infinite project list. Have fun.

[tggzzz]

My first experience with Unix was on a PDP11, Xenix made by that well known company - Microsoft.

[Gyro]

That brings back memories, I worked for DEC for about 12 years. I even ran a PDP-11/05 (Unibus), with proper Core memory, as a 'home PC' for quite a while. It was initially equipped with with a pair of dual TU56 DECtape 1s (random access 1" tape  ) all in a home made melamine chipboard cabinet. Later I 'upgraded' to a dual RX02 8" floppy, before jumping to Q-bus 11/03 -> 11/23+ -> 11/53 with standard MFM 5 1/4" HDDs and RX50 5 1/4" floppies.

Working there, there were always piles of old discarded boards and card frames lying around if you knew where to look. I used RT11 as my OS throughout, with Runoff for word processing (we used that for all our specs anyway) and various other stuff off the DECUS tapes.

[Ampera]

Those look so neat, I'd absolutely love to one day own, or at least play around with any number of the DEC minis. I consider the PDP-11 in particular to be the taxonomic root of modern personal computing, and to even see one in person would be sweet. Damn things look like they were out of Star Trek.

[intabits]

That brings back memories, I worked for DEC for about 12 years. I even ran a PDP-11/05 (Unibus), with proper Core memory, as a 'home PC' for quite a while. It was initially equipped with with a pair of dual TU56 DECtape 1s (random access 1" tape  ) all in a home made melamine chipboard cabinet. Later I 'upgraded' to a dual RX02 8" floppy, before jumping to Q-bus 11/03 -> 11/23+ -> 11/53 with standard MFM 5 1/4" HDDs and RX50 5 1/4" floppies.

I also have an 11/05 with core memory, but no TU56's.
DECtapes were my favorite, I wanted wanted one of those most of all...

[GregDunn]

Unfortunately, I never landed a PDP-11 but I managed to pull an RK05 pack and a KDJ11-B CPU out of the recycle when my old workplace was being closed down.  Totally useless without the actual mainframe and related hardware, but they hold some nice memories.

[intabits]

Just added many hi-res photos of the boards in these machines to the gallery at:-
https://imgur.com/gallery/1czglgJ

[PA2HK]

Nice machines and a very nice collection you have there. Also own a PDP11/34, it is a KD11-EA version with a FPU and cache unit, that makes the machine a 11/34c. I rescued the machine in the mid 1980s from a computer demolition/scrap plant, machine used to be belong to Twente University in the Netherlands and currently has a Plessey RK05F (clone) and DEC RX02 drives. Both drives did not originally belong to the PDP11 and came from another unit. Many years ago I used my "Elfje" at home to run RT11 and to experiment with early BSD Unix. Machine is sitting in heated/dry storage in an original DEC 19"rack and has not been used in years, it needs to be restored before it can be used again. Luckily I have lots of spare parts, RK05 discs, documentation, original schematics all rescued from that era. One day she will run again.

[intabits]

Nice machines and a very nice collection you have there. Also own a PDP11/34, it is a KD11-EA version with a FPU and cache unit, that makes the machine a 11/34c. I rescued the machine in the mid 1980s from a computer demolition/scrap plant, machine used to be belong to Twente University in the Netherlands and currently has a Plessey RK05F (clone) and DEC RX02 drives. Both drives did not originally belong to the PDP11 and came from another unit. Many years ago I used my "Elfje" at home to run RT11 and to experiment with early BSD Unix. Machine is sitting in heated/dry storage in an original DEC 19"rack and has not been used in years, it needs to be restored before it can be used again. Luckily I have lots of spare parts, RK05 discs, documentation, original schematics all rescued from that era. One day she will run again.

I also have 2 RK05 drives, but they came with a PDP8/A. For the 11/34 (or maybe it was the 11/05?), I have 2 RX01 drives and  some diskettes.
I've only ever toggled in short test loops on any of my PDPs, and I'm not sure if I want to get much beyond that again.  I suppose running RT11 from the RX01s is fairly doable, but the RK05s scare me!

[xrunner]

Yes youngsters out there - the keyboard is not supposed to have digits 8 or 9. 

[intabits]

I've just done a teardown, clean, checkout, repair, modify and test of the H777 power supply from the PDP-11/04.

The H777 PSU




The main +5v @25A regulator PCB




The "MOS" regulator PCB, providing +/-15V @1A (and a smaller +5V @4A supply for use by a battery backup system)




At over an hour, the video is quite long, (and that's been distilled down from over 3 hours of recording).
But I think that anyone who is very interested in this topic, and especially anyone planning a similar exercise, would want to see as much detail as possible. Hence the long video.

For those not so inclined, the executive summary is:- 
 
* Teardown and clean of the PSU.
* Reform the 3 large electrolytic capacitors.
* The 3900uF/6V cap on the 5V supply output is bad (which might be a chronic failure point for these units).
* A salvaged replacement cap is bodged into service.
* Testing reveals that the +/- 15V, and +5VB supplies (from the MOS regulator board) are good,
* But the +5V supply from the main regulator is producing no output.
* The +5V supply is found to be in current limit mode.
* When investigated out of the case, the +5V supply comes good.
* No obvious cause is found, but it's suspected that the replacement capacitor, and/or regulator module were reinstalled incorrectly.
   Further suspicion falls on the interference fit of the PCB modules inside the unit.
   Theory of failure is that this tightness is causing mechanical stress that may be affecting some components or solder   joints.
* The two tall 560uF/20V capacitors on the MOS regulator PCB were replaced with modern 1000uF/25V caps that are much shorter, and so eliminate the interference between the PCBs.
* Unit is reassembled and all voltages are good.
* A connector and cable harness are made to attach the PSU to a set of dummy loads.
* All supplies operate satisfactorly at near rated load (but only at about 19A on the +5v supply).
  The need for a better dummy load for the +5V supply is clear.


The video:-
https://youtu.be/MpV6pyaxZ6M

Links:-

Mattis Lind's (DatorMuseum in Sweden) PDP-11/04 restoration, with similar H777 PSU issues:-
http://www.datormuseum.se/computers/digital-equipment-corporation/pdp-11-04


Documentation resources at BitSavers:-

861B Power controller:-

http://www.bitsavers.org/pdf/dec/powerSupply/EK-861AB-OP-001_861-A_B_C_D_E_F_Power_Controller_Users_Manual_Nov76.pdf


BA11-L mounting box (used for both 11/04 & 11/34, contains extensive H777 theory of operation)

http://bitsavers.trailing-edge.com/pdf/dec/unibus/EK-BA11L-TM-001_Oct77.pdf
http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-11-HBKEF-A-D%20BA11-K%20Mounting%20Box%20Manual.pdf


PDP-11/04 Engineering drawings (H777 PSU starts at P104):-

http://bitsavers.org/pdf/dec/pdp11/1104/MP00019_1104_EngrDrws_Feb78.pdf


PDP-11/34 Engineering drawings (H777 PSU starts at P183. Component overlay is more legible):-

http://bitsavers.trailing-edge.com/pdf/dec/pdp11/1134/MP00082_1134_Vol2_Sep76.pdf

[Halcyon]

Thanks for posting! I love the slots on the mainboard, they look insanely robust!

[intabits]

Following on from the checkout, fix, modify and test of the H777 power supply from my PDP11/04, the exercise is repeated for the PDP11/34 PSU.

For my future reference and hopefully that of others, I note the differences found between the two PSUs, plus steps to take (or avoid) that I found helps streamline disassembly and reassembly.

The same problems were found as for the PDP11/04 PSU:-
  - 3900uF/6V cap on +5V output was bad
  - Replaced "too long" 560uF/20V capacitors on the +/-15V supplies
Plus, the fan worked, but not very well, and needs to be replaced.

A quick test under load confirmed the output voltages were OK.

Finally, both PSUs were reinstalled into their BA11-L mounting boxes, and checked that the console power switch operated the supplies. (No boards inserted yet)




Video:-