PDP-11/35 Restoration, Part 3

More vacuuming, and started using distilled water and clean rags to wipe up surface dirt on the chassis, front panel, and cables.

To switch gears a little and pulled the DSD-440 dual 8″ floppy drive from the rack and and cleaned the chassis with a soft damp rag. Upon opening it up I discovered that the interior is almost pristene! Very little dirt inside. This bodes well.

PDP-11/35 Restoration, Part 1

My first night of restoration! I started by getting hundreds of photos of everything from every angle, so I could document the original state as best I could. I also made note of the system configuration before I started to touch anything.

Next, I did a little gentle vacuuming of the surface dirt. There was plenty of it. Fiberglass insulation had become packed into some areas of the card cage, along with the remains of insects, some live spiders, and a few acorns. I sucked this out as best I could.

The original state, as seen here, is just disgusting, really.

PDP-11/35 Card Cage
Mouse-nest infested and very dirty BA11-D chassis

After some light vacuuming, I began to remove cards. I started with the four farthest to the right, the M7232, M7231, M7233, and M7235. Each card I pulled was photographed so I could know its original state, gently washed in warm soapy water, and rinsed with distilled water before being allowed to air-dry in front of a fan. Remarkably, the cards so far are in great condition! There’s some corrosion and spotting here and there, but nothing so bad that I think the electronics won’t work. Mainly it’s bits of surface rust and discoloration on chip leads, nothing worse.

PDP-11/35 Details

Here’s a little more information about the PDP-11/35.

It came to me with the following peripherals:

  • ECCO Paper Tape Reader
  • Diablo Series 30 disk drive — compatible with DEC RK05
  • Applied Engineering 2200 Disk Controller for the Diablo Series 30
  • Data System Designs DSD 440 floppy disks — compatible with DEC RX02
  • DEC H750 Power Supply

There are three backplanes (or “System Modules”, as DEC called them) installed. The first is a 9 slot KD11-A, the second is a 4 slot MM11-S, and the third is a 4 slot DD11-A. The MM11-S is interesting in that it suggests that the 11/35 originally came with the MM11 16KW core memory option, though somewhere along the line that was upgraded to MS11 MOS memory.

Here’s the layout:

A B C D E F
01
02
03 M7232 – KD11-A 11/40 Micro Word Module
04 M7231 – KD11-A 11/40 Data Paths Module
05 M7233 – KD11-A 11/40 IR Decode Module
06 M7235 – KD11-A 11/40 Processor Status Module
07 M7234 – KD11-A 11/40 Timing Module
08
09 M981 Jumper M7800 Async Serial
10
11 M7847-BD – MS11-EP 16KW RAM 1
12 M7847-DJ – MS11-JP 16KW RAM
13 M920 Jumper
14 DSD 440 Floppy Controller
15 ECCO Paper Tape Reader
16 G772B M7800 Async Serial
17 M9302 Terminator G727A
  1. The MS11-JP module is normally an 8KW board, but this one has been field upgraded to 16KW of MOS RAM, minus parity bits on the upper 8KB.

Rescuing a PDP-11/35

On Sunday, April 28 2012, I picked up a PDP-11/35 from a friend who had been storing it in a shed for many years. The system has been home to generations of spiders and mice, and needs more than just a little bit of TLC.

The PDP-11/35, dirt and all
The PDP-11/35, dirt and all

The provenance of the machine is kind of interesting. The friend who gave it to me grabbed it from the loading dock at ATARI in Milpitas, California, when it was being scrapped. They were apparently using it in some kind of standards or verification engineering role, but it’s not known what. He later moved to Washington state, where the machine was stored in a shed for some time. Unfortunately, the climate and the local wildlife took their toll.

I’ll document ongoing progress on restoration here on the blog. Luckily, my initial inspection suggests that things are not as bad as they look. The electronics are in fair condition, with only very little surface corrosion on some IC leads. The metal chassis and power supply case have some bad surface rust, but can be stripped and re-painted. The front panel and switches are mechanically sound. I think it is definitely worth restoring!

Computer Journalism in the Dark Ages

I’ve recently been reading Brian Bagnall’s book On the Edge: The Spectacular Rise and Fall of Commodore. It’s a good read, if a little rough in places and perhaps in need of more judicious editing.

But while reading it, I’ve also kept some source materials by my side. Thanks to modern technology, I have my iPad with a collection of Byte magazine from the late 1970s sitting next to the book, and it’s been fun to go find the original articles that Bagnall sourced for his work.

This morning I was reading about the launch of the Commodore PET 2001 at the 1977 National Computer Conference in Dallas. The segment in Bagnall’s work mentioned a positive review in Byte by Dan Flystra, so I looked it up. What struck me immediately was the date. The computer was ordered by Flystra in June, 1977. The review was written in October, 1977. And at long last, it was published in March, 1978.

This seems remarkable now. From product purchase to review in subscribers’ hands: nine months, the length of time it takes to make a human being. Even disregarding the long lag time between order and delivery (vaporware is timeless, after all), we’re left with five months between review and publication. In an age of Twitter and Facebook, this seems incredible, absurd. Yet, I remember these times. They occurred within my lifetime.

That makes me feel old.

How far we’ve come. Think about it the next time you watch an unboxing video of some new gadget on Youtube that was filmed an hour earlier, and just two days after the order shipped direct from Shenzhen, China.