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Restoration of a PDP11/60

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klapperp

Experienced Member
Joined
Dec 14, 2021
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221
Location
Austria
Dear Community!

A year ago I swapped one of my PDP11 systems with a very complete PDP11/60 system.

20250203_193909.jpg20250221_164904.jpg20250221_164842.jpg20250221_164923.jpg

Now we started to restore this beautiful artefact and of course we need your help.
First we will rework the PSUs and we are searching for the schematics of H7440 regulators.
The documents are mentioned on page 49 in EK-11060-SV-01_1160cab_Feb78.pdf:

Circuit schematics for the regulator boards used in the Н7440 and Н781 regulators are shown in drawings D-CS-5411793-0-1 and D-CS-5411774-0-1.

If anyone has a copy of these drawings and/or knows where to find them please let me know!

Your help is highly appreciated!
Thanks in advance and kind regards,
// Peter
 

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Hello Peter.
That is a very nice machine indeed.
Are the schematics of that PSU not on bitsavers?
If not, maybe Henk Gooijen might be able to help you, as he also has a 11/60.
Henk is a personal friend of me and is also on this forum,

Regards,
Ed
 
klapperp said:
Circuit schematics for the regulator boards used in the Н7440 and Н781 regulators are shown in drawings D-CS-5411793-0-1 and D-CS-5411774-0-1.
Click to expand...
Note that these drawings are parts of FMPS MP00085 and MP00084, respectively. These FMPS are listed on Manx:
Manx states for both "No copies known to be online."

Possibly they are included in FMPS MP00410 for the BA11-P:
Manx states for "No copies known to be online."

Have either of these SMPS failed, or are you just collecting possibly useful documentation?
 
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Backplanes and power supply schematics show up in many other print sets, you need to spend some time searching. The easiest way (not easy) is to open the FMPS table of contents and look for the unit, then scroll down to that approximate area. I got a hint from a google search to look for the H7440 schematic in the RM05, but nothing on the H781, though I didn't spend much time on it.

The 5411793 schematic starts on page 144 of https://bitsavers.trailing-edge.com/pdf/dec/disc/rm05/MP01075_RM05_Part1.pdf

CW
 
I have several FMPS (Field Maintenance Print Sets) of PDP-11 systems, and I seem to remember that some of them contain a description of the power supply chassis, and the H7xxx "power bricks".
Nice to see that this 11/60 found a new owner. I did know its existence, but a trip to Vienna was a bit too far of a drive for me. When the temperature gets better in my "museum" (it is now just 8 degress Celsius), my plan is to get my 11/60 running. It can single step instructions, but when it runs "at full speed" the CPU crashes.
 
I did a quick check. In the 11/40 System Manual, the H742 power supply is described, and the H744, H745 and H754 are described, so my guess is that the schematics are included in the 11/40 FMPS.
I seem to remember that the H7440 is also used in the power supply of an other PDP-11 but can't remember.
Is the H7440 only used in the 11/60??
 
@Henk we found the schematics of the PSUs inside the RM05 documentation. Thanks again to @Bitly who gave us the crucial hint.

We will replace all the large capacitors with something newer rather than try to reform them because after 45 years it is very likely that they are dried out.
We first want a fully stable power source before we dig deeper into the logic parts of the system.

In the past I had expereinces with strange effects related to unstable PSUs and therefor, for me a stable power source is the pre requisite for anything else.
 
Ok, great find! As far as I know, the PSU in my 11/60 is OK, but it still is nice to have documentation when you need it.
I did find that the H7440 is also mentioned in the RM03, but it was only in a schematic block diagram, no details.
 
As we have in total five H7440 PSUs we started with these, to replace the capacitors. We want to use something which is suppoesed to work also in a few years from now. Therefor we created PCBs which fit at the original place of the big old capacitors.

First we created some mechanical models to see what is possible:
signal-2026-01-13-17-16-28-611.jpgsignal-2026-01-13-17-16-28-611-1.jpgsignal-2026-01-17-22-33-58-637.jpgsignal-2026-01-17-22-33-58-637-1.jpgsignal-2026-01-17-22-34-32-147.jpg

And after we decided what is the best solution, we produced PCBs which perfectly fit at the original places:
signal-2026-02-05-19-34-13-515.jpgsignal-2026-02-05-19-34-13-515-1.jpgsignal-2026-02-05-19-34-13-515-2.jpgsignal-2026-02-05-19-34-13-515-3.jpg

To be continued as soon as we made some tests under load ...
 
Now we have a proof of concept that it works.
Here the setup how wetested the PSU with the two replacement PCBs:
signal-2026-02-06-19-01-36-678.jpg

And here the video which my colleague Konstantin made during the test:

We will now upgrade all H7440 PSUs in the system before we create a similar solution for the the H781 and the H7850 PSUs.

To be continued ...
 
After our successful tests we will now rework a total of five H7440 PSUs in our PDP11/60

There will be some PCBs left after this.
If somebody is interested you can contact Konstantin directly or just let me know.

After this we will rework the next PSUs in our PDP11/60.
 
This is neat! Would you mind open-sourcing your PCB design and BOMs? I have a few H744s awaiting restoration, and i believe the 31000uF capacitor is exactly the same.
 
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nadaveiron said:
This is neat! Would you mind open-sourcing your PCB design and BOMs? I have a few H744s awaiting restoration, and i believe the 31000uF capacitor is exactly the same.
Click to expand...
Hello, Thankyou!
I will probably Upload the Design Files (Gerbers, Schematics & BOM's) on the PCBWAY Shared Projects Page, and eventually later to the JLCPCB Shared Project page. Just for Info, I used 2oz Copper for these PCB's.

Mounting and the rest mechanics are shown in my Video.

Cheers,
Konstantin
www.youtube.com

Konstantin Grigoriadis

Power Electronics, Analog, RF, High Voltage and Vacuum Tubes, Reviews, Repairs and Teardowns are the Main Topic of my Channel, further I make Vintage Computer Repairs and at last some Travel Videos :-) I started the channel initially as a way to show Status updates of my Electronic Prototyping...
www.youtube.com www.youtube.com
 
Hello, Bellow the Links to the "my PCBWAY Shares Projects" Page with the Files for the 2 Replacement PCB's I designed,
for the Obsolete 31000uF Input and 6000uF Output Capacitors of the H74400 & H781 DEC PDP11/60 Buck Converter PSU's.

Cheers,
Konstantin

www.pcbway.com

Digital Equipment Corporation (DEC) PDP-11 H7440 & H781 PSUs 31000uF Electrolytic Capacitor Replacement using a PCB Based Solution - Share Project - PCBWay

This is a very Specialized Project I Designed to be able to Replace a 31000uF/50V Large Vintage 1977 Obsolete Electrolytic Capacitor on aDigital Equipment Corporation (DEC) PDP-11/60 H7440 and H781 5V...
www.pcbway.com
www.pcbway.com

Digital Equipment Corporation (DEC) PDP-11 H7440 & H781 PSUs 6000uF Electrolytic Capacitor Replacement using a PCB Based Solution - Share Project - PCBWay

This is a very Specialized Project I Designed to be able to Replace a 6000uF/10V Large Vintage 1977 Obsolete Electrolytic Capacitor on aDigital Equipment Corporation (DEC) PDP-11/60 H7440 and H781 5V ...
www.pcbway.com

More Details of the Design in my Youtube Video:

www.youtube.com

Konstantin Grigoriadis

Power Electronics, Analog, RF, High Voltage and Vacuum Tubes, Reviews, Repairs and Teardowns are the Main Topic of my Channel, further I make Vintage Computer Repairs and at last some Travel Videos :-) I started the channel initially as a way to show Status updates of my Electronic Prototyping...
www.youtube.com www.youtube.com
 
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