Looking for memory for PDP 11/45

[pbirkel@gmail.com]

When you have time, can you please tell me the make and model of all memory related components you have? For example, if I just buy memory I suspect it won't work without a "memory control" as well. I'm hoping to find some on vcfed marketplace or eBay.

An as-shipped memory configuration for an 11/45 would have used either the MF11-L/LP, MM11-U/UP, or MF11-U/UP according to DEC configuration literature. These were all multi-module low capacity stacks so several stacks would have been installed, requiring additional special power regulators (which you don't have), unique backplanes (which you don't mention having) and space. Reference documents:

http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-11-HMFLA-C-D%20MM11-S,%20MF11-L,%20and%20MF11-LP%20core%20memory%20systems.pdf

http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-11-HMFMA-B-D%20MF11-U-UP%20Core%20Memory%20System%20Maintenance%20Manual.pdf

If you want to use DEC memory then your best bet is MOS memory installed in a standard DD11-D backplane (as suggested by others) plus the correct power regulators for that backplane. For the backplane, see:

http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/unibus/MP-0DD11-D0_DD-11D_Engineering_Drawings_Feb77.pdf

For MOS memory probably your best bet is some variant of the MS11-L; the MS11-L is still "around in the wild". A good choice might be the M7891-B (64Kw). There's an equivalent half-populated M7891-L listed on eBay at the moment: https://www.ebay.com/itm/225768623109 (the listing states the full 128K capacity of this board but it's not been fully populated). IMO a fair price would be half of the listing price. Reference document:

http://www.bitsavers.org/pdf/dec/pdp11/memory/EK-MS11L-UG-001.pdf

I suggest that you intensively study your current configuration as it doesn't seem to be complete, at least power-wise.

In case it's not already clear, this system will require lots of TLC before you can "just plug it in" and expect anything to "just work". I strongly suggest approaching it step-wise with all modules removed and testing/verifying all power supply rails under load. If you're not familiar with reforming electrolytic capacitors then that's a topic that you'll need to "get under your belt" before you simply plug in those H742s (yes there's an internal regulator in each that include an electrolytic capacitor that should be reformed).

If this all sounds "too complex", that's because it is :->. That's how it was 50 years ago ...

 

[MattisLind]

The H754 is a +20V / -5V regulator and it support the newer core memory systems that DEC made. The older used -15V. MM11-U requires +20V / -5V for example.

I am not sure if lacking a -15V supply is a problem, really, if you aren’t using the older core memories.

 

[pbirkel@gmail.com]

I am not sure if lacking a -15V supply is a problem, really, if you aren’t using the older core memories.

Well, the manual(s) indicate that -15Vdc from Slot F should be supplied to rows 1, 2 (FRH), and 15 (TIG), so I'm inclined to think that it's important. And the manual(s) also indicate that an H745 is part of the minimal configuration (see Table 1-1, page 1-4, slot E), so I'm inclined "to give DEC the benefit of the doubt" that one is required, somewhere more than the supply internal to the H742 :->. I suspect a typo in the OP list, but that needs to be confirmed. Would be interesting to know in which slots the existing regulators are located.

 

[MattisLind]

You’re right! Good that you checked! So the timing generator needs -15V for something. Perhaps the 33 Mhz oscillator circuit is using it?

It could indeed be a typo on the behalf of the OP. H745 vs H754.

 

[obsol33t]

Thank you everyone for the helpful replies. I've been buying components for this system for about ten years but never put it all together. Visually it looks nice in three H960 racks, but my goal is to one day restore every component. I am aware that capacitors need to be reformed and have a variac, though I've never done that kind of work before. When the time comes, my plan has been to focus on the power supplies first before moving onto the processor. That will require a lot of reading to build a deep understanding of what I have and how it should be. Eventually after getting the processor working I'll move to peripherals. My PC05 was rebuilt by the guy who sold it to me, but the rest of the components would be opened up, cleaned, capacitors reformed or replaced, etc. This will be a large project and at this point in time I'm just trying to buy all of the components that I'll need to get this system running again.

I have a soldering rework station, oscilloscope with power analysis module, multimeter, power supply for electronics work, and friends who know how to use these tools much better than I do. My background is in computer programming, so the complexity of hardware doesn't scare me though I admit that I have a lot to learn. Especially about DEC systems. I'm happy to do a lot of reading when I have the time to dedicate to it. I also have a PDP Straight-8 and VAX 11/780 that need attention.

I took photos several years ago when we were taking the machine apart to bring it into my basement and re-assemble. Attached is a photo of a series of power supplies that I mentioned earlier. I found another photo that shows two h7420a power supplies in that area when viewed from the front of the rack, and I seem to remember there were more power supplies than shown because I had to disconnect many cables from them in order to take it all out. I took notes and photos to help me put them back correctly.

Things are getting busy around Christmas, but sometime during the break I will pull that rack out and see what other power supply related components I can find. I know there is a power distribution box at the bottom. I will take some clear, detailed pictures of the processor unit, all around.

 

[MattisLind]

The PSU of the 11/45 has two h742. In my the upper is connected to the switched section of a 861 power controller while the lower is connected to the unswitched section.

As Paul says you need a H745. It should be in the lower unswitched H742.

The H754 in the upper h742 indicate that your system had a core memory system at some point in time.

 

[daver2]

I was just going to say the same thing.

Mine has two (2) racks of supplies - upper switched and lower non-switched - exactly as stated above.

Dave

 

[pbirkel@gmail.com]

I am aware that capacitors need to be reformed and have a variac, though I've never done that kind of work before.

And you won't this time either. A variac may be used for a linear PS. These are switched-mode regulators. You need to at least partially disassemble and use a current-limiting DC power supply (or an equivalent arrangement of resistors and lower voltages over time) to reform the electrolytic capacitors in each regulator, including the one that is a built-in of each H742 (or in your case H7420 A, both upper and lower). Inspect carefully first; although DEC used quality electrolytic capacitors some have deteriorated anyway with evidence of leakage around terminals. Some may not reform well (high trickle current despite reforming); an ESR meter may become useful at that point. Replacements can still be obtained with a bit of search, but they aren't exactly cheap.

 

[daver2]

+1, current-limited DC power supply for reforming capacitors.

All of the capacitors in my supplies were successfully reformed except one power supply unit. For some reason, these capacitors had leaked and need to be replaced. My next job...

Dave

 

[pbirkel@gmail.com]

The H754 in the upper h742 indicate that your system had a core memory system at some point in time.

One would think so. There are three SUs there; the middle one appearing to a Plessey "DISC CONTROLLER" (perhaps an RK11-D workalike) The forward one appears to be a DD11-C. The rearward one I'm uncertain about; possibly it's an "old school" SU with FastOn tabs instead of the usual Molex wiring harness that supports third-party core memory?

 

[obsol33t]

I finally got around to pulling the rack out and looking at the power supplies. This is what the 11/45 has installed:

• H754 x1 +20V 8A, -5V 1A
• H744 x4 5V 25A
• H745 x1 -15V 10A
• H7420 a x2 (no details)

There is also a power distribution unit at the bottom. I will attach some photos of the power supplies and some stickers with information from the unit. You might notice the cables have been disconnected from the power supplies. This was done while disassembling the rack to bring it into my house. I made detailed notes before and during disassembly and left the cables disconnected knowing that I will need to test, repair and possibly reform the capacitors of each power supply.

Just a reminder, I'm looking to find out exactly which memory card I can buy on eBay or elsewhere for this machine.

 

[obsol33t]

And you won't this time either. A variac may be used for a linear PS. These are switched-mode regulators. You need to at least partially disassemble and use a current-limiting DC power supply (or an equivalent arrangement of resistors and lower voltages over time) to reform the electrolytic capacitors in each regulator, including the one that is a built-in of each H742 (or in your case H7420 A, both upper and lower). Inspect carefully first; although DEC used quality electrolytic capacitors some have deteriorated anyway with evidence of leakage around terminals. Some may not reform well (high trickle current despite reforming); an ESR meter may become useful at that point. Replacements can still be obtained with a bit of search, but they aren't exactly cheap.

Thank you for bringing this to my attention. I will not attempt to work on the power supplies until I've learned a lot more, and possibly with the help of a couple friends who know a lot more about electronics repair than I do. I have a Keithley 2231A-30-3 power supply that may be helpful.

 

[pbirkel@gmail.com]

Just a reminder, I'm looking to find out exactly which memory card I can buy on eBay or elsewhere for this machine.

While you do have the right power supply module installed for core memory (H754) that doesn't tell us which core memory was originally installed, which will be dependent on the backplane that was installed. You'll need to look at the labels on the sides of the backplanes to figure that out. Once you've figured out what backplane is installed then you can examine the corresponding technical documentation to determine the correct _set_ of modules that will be required to populate that backplane.

Your backplane photo shows three 4-row system units to the right. See my comments: https://forum.vcfed.org/index.php?threads/looking-for-memory-for-pdp-11-45.1237126/post-1355827

Regarding a specific "memory card" in the absence of knowledge of the installed backplanes, see my comments: https://forum.vcfed.org/index.php?threads/looking-for-memory-for-pdp-11-45.1237126/post-1355762 And then Mattis comments, indicating that MM11-U/UP likely, however I believe that MF11-U/UP is also possible.

The MM11-W (similar to the -U) requires four modules:

H224C	32K (16K Sense) 18-Bit Stack on 50-
G116	20-Bit Sense/Inhibit, 32K, (Dual 16K Sense), Hex
G236	32K X-Y Drive, Current Source, Decode, Hex, MM11-W,-WP
M8294	32K Timing & Unibus Interface, MM11-W,-WP, Quad

The MF11-U also requires four modules:

M8293	16K Unibus Timing Module
G114	Sense Inhibit Module
H217C	Stack Module (18 bits including parity)
G235	X-Y Driver

The problem is that I believe that both of these core memories are only supported by 9-slot backplanes (thus holding two sets of modules), and you only have a 4-slot backplane. Which makes me think that you had later-type core memory which integrated to a 2-slot package with the core module piggybacked to the drivers/sense/timing module. Further guessing will be exactly that. You need to check the labels on all three of your 4-slot backplanes to narrow down the what-is-possible, unless you decide to use MOS memory that is supported by a standard DD11-C (what you seem to have in the last position, far-right).

 

[MattisLind]

There are also the MM11-B, MM11-C and MM11-D modules which fits in any standard MUD slot. These are sandwiched modules comprising a core memory array and a driver board that connects directly to unibus without any need for a special backplane. The MM11-D is +20 / -5V. I think the other two are the same.

If you just want a MOS board there are for example M7891, MS11-L which give you the full 256k in one single MUD slot. There were also third parties that made similar boards.

 

[pbirkel@gmail.com]

There are also the MM11-B, MM11-C and MM11-D modules which fits in any standard MUD slot. These are sandwiched modules comprising a core memory array and a driver board that connects directly to unibus without any need for a special backplane. The MM11-D is +20 / -5V. I think the other two are the same.

If you just want a MOS board there are for example M7891, MS11-L which give you the full 256k in one single MUD slot. There were also third parties that made similar boards.

Yes. All possible substitutes. One continues to wonder what was originally provisioned :->.