A Small Detour: PDP-11 Rescue!

(I do have some new MDP-1000 information, I do, really.  There's even some at the end of this post.  So read on!)

Sometimes you gotta do something stupid for your hobby.  Like, really, really stupid.  This is one of those times. Back in October, a post appeared on the Vintage Computer Forums:

In case it's not clear from the text, a collector in Silicon Valley was looking to part with a pile of PDP-11 systems that had been in a fire many years ago.  Here's a couple of larger pictures:

What we have here are two of the more interesting (and desirable) blinkenlights PDP-11 systems:  A PDP-11/70 and a PDP-11/45.  Unfortunately, neither of them looked to be in particularly great condition -- the 11/45 in particular looked like it spent some time in a blast furnace.  My first thought was that these systems were a lost cause.

But.

But but but.

The 11/70 is on my short list of "Computers I Just Gotta Have" but they're rare enough, and sought out enough in the collector community that finding one for a price I can afford seems almost an impossibility.  (The 11/45 is a really nice computer, too.)

Hmm.

Despite their condition, I was intrigued, and so I reached out to the seller who informed me that I was the only one who'd contacted him, which I still find very surprising.  I don't live in California but I have a friend who lives near the seller, and he kindly offered to go out and take some more detailed pictures so I could more accurately assess the condition of the systems.  

And wouldn't you know it, things didn't look so bad on the inside:  Here's a few shots of the innards of the 11/70:

Filthy, yes.  Melted?  Not so much.  Except for those fans at the top there, where the plastic fan blades kind of became liquid and dripped down on everything below them.

Melty!

Apart from the melted front panel and fans, the thing looked totally fine.  Backplane clean, wirewrap undamaged, power supplies present, CPU board set complete.  And more interestingly, take a closer look at the cards in the card cage in that first picture there.  Those of you keen of eye and well-versed in PDP-11/70 lore might notice the "Setasi" label on the boards on the left-hand side.  That's an aftermarket boardset -- the Setasi Hypercache + PEP70, which replaces the original memory and cache of the PDP-11/70 system.  It gives the system a full 4MB of memory, and that memory runs at the speed of the 11/70's cache.  It's a rare upgrade, and aside from making the system faster, it's really useful:  normally the 11/70's memory resided in an external rack and took up multiple cabinets with their own large power supplies.  The PEP70 provides an entire 4MB of memory on a single board!  Here's another view of those boards:

Oh yeah.  That's the stuff right there.

Well, that's tantalizing, for sure.  But what about the 11/45?

It's a bit more rough.  In that top picture you can see that in addition to the front panel being melted away, the power distribution wiring harness is completely toast.  And there's not much paint left on the thing and rust has taken its place.  But again, the boards are all there and look to be in decent nick (apart from a slightly melted handle on that M9301 Bootstrap Terminator there in front).  And miraculously the backplane looks to be completely unharmed, apart from some charred detritus stuck in the wirewrap pins.  It seems like the metal of the chassis and the power supplies shielded the processor from the brunt of the heat.

Needless to say I decided to take the plunge.  I had already been planning a trip to the bay area to pick up some other items and to help out a friend with a Xerox Alto restoration, why not add a couple of rusty racks worth of slightly melted PDP-11 gear to the haul?  I struck a deal with the seller, and the first weekend in November I rented a cargo van and drove 14 hours from Seattle, WA to Cambpell, CA.  

All told, that weekend I picked up the two PDP-11s, a Three Rivers PERQ 1A workstation, two General Automation SPC-12 minicomputers, a Symbolics 3620 workstation, a pile of Symbolics and TI Explorer documentation and parts, and two Unibus memory cabinets that might have been a part of C.mmp at one point.

Oh, and a replacement front panel for the 11/70, kindly sold to me at a very reasonable price by a good friend of mine:

Is there anything more beautiful?

Then I got in the van and drove back.

Over the past couple of weeks I've been slowly going over the two PDP-11 systems, preparing a plan to tackle their restorations.  I've decided to start with the 11/70 since it's the cleaner (and more exciting) of the two systems.  The rack has been lightly sanded down and cleaned, so it's no longer covered in a gritty layer of rust and soot and melted plastic, and the same process has been started for the processor chassis.  Once spring rolls around I plan to repaint the rack and the chassis, but for now I just want them clean enough so that my hands don't get filthy when I work on them.

The next step is to clean the backplane and the boards and then tackle restoring and testing the power supplies.  I've ordered a ton of isopropyl alcohol for cleaning the backplane slots, and once it arrives the cleaning can commence.

What about the MDP-1000, huh?

Sure, sure.  Recall that I mentioned picking up a couple of SPC-12s in my California haul?  Well, here they are!

As I mentioned in my last post, the MDP-1000 is a rebadged/repackaged SPC-12.  Now I have the original to hack on as well!  And I have some documentation for these!  More information in my next post, I swear!

Until next time!