Well, 2022 came and went without a post from me, and I apologize. Oh, and most of 2023. Sorry. I had plans, honest. I still have plans actually and maybe sometime in what remains of this year I can actually do something about them. I started posting on Mastodon (if that means anything) you can check it out right here , I sometimes post more than once a month, can you even stand it? I started…
Whither PDP-11/70 Updates? You know, I'm glad you asked. Well, not glad, but also not unhappy that you asked. Just kind of a calm, lukewarm tapwater of feelings because you asked about this. Actually, no one has asked about this. I don't think anyone reads this blog, that's fine, I mostly do this because every now and then the weasels in my skull get loud enough that I need to vent the pressure,…
Ahem. Sorry about that, seems like I forgot what I was doing here. Where was I? February 9: The Saga of LOAD ADDR When we left off, the 11/70 was showing signs of life but wasn't executing instructions and, more pressingly, the "Load Addr" switch would stop working after the system warmed up for a minute or so. Some experimentation revealed that the switch itself was still functioning (eliminating…
January 2021: Debugging Commences In my last post I left off my tale of PDP-11/70 restoration in late January, having just powered up the rebuilt supplies after reinstalling them in the chassis. The next step was to reinstall the processor, cache, and memory and see what happens: (not quite) The First Power-up with Stuff Installed The answer is: not much. The processor was almost entirely…
Looks like a few months have passed since my last post, as seems to be typical. Never you mind, let's just ask the question: How'd that whole "Restore a rusty soot-covered PDP-11/70" thing turn out? Well, I don't want to spoil anything. Let's pick up where we left off. November 2020:Make it Look Good Looking good! Well, first I installed the replacement front panel assembly. That'll get you 90% of…
(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…
So having found myself gainfully employed again after a rather stressful hiatus over the summer, I decided to reward myself and splurge on this sexy bit of kit: The Motorola MDP-1000 Minicomputer Prior to this showing up on eBay, I wasn't even aware that Motorola had ever made a minicomputer (more on that later), but there it was. I knew I had to have it. It arrived last week and I've been digging…
As you might have heard, Living Computers: Museum+Labs has shut down; its doors will remain closed for at least the next twelve to eighteen months, and the staff is off to find new adventures. I have had the honor of being an engineer at LCM+L for the last five years and I am still struggling to come to terms with this -- I've had time to let the shock settle in since I heard the news a month ago…
In our last installment our intrepid adventurer had gotten the Interphase 2181 SMD controller running again, and had used it to do a low-level format of a gigantic 160mb Fujitsu hard drive. This left him with all the ingredients needed to put together a running LMI Lambda system, at least in theory. Tapes and Tape Drives I had intended to wait until I’d found the proper 9-track tape drive for the…
Continuing from the conclusion of my last post , I had gotten to the point of testing the LMI’s Interphase SMD 2181 disk controller, but was getting troubling looking diagnostic output: SDU Monitor version 102 >>/tar/2181 -C Initializing controller 2181: error 3 test 0 Alarm went off - gave up waiting for IO completion 2181: error 3 test 0 Alarm went off - gave up waiting for IO completion 2181:…
In our last exciting episode , after a minor setback I got the Lambda’s SDU to load programs from 9-track tape. Now it’s time to see if I can actually test the hardware with the available diagnostics. Tape Images Tape images of the Lambda Release and System tapes are available online. Daniel Seagraves has been working on updating the system and has his latest and greatest are available here . A…
After working on the Lambda’s monitors as described in my last writeup , my next plan of action was to see if I could get diagnostics loaded into the SDU via 9-track tape. ROM Upgrade Time SDU Monitor, Version 8 But first, I wanted to upgrade the SDU’s Monitor ROM set. The SDU Monitor is a program that runs on the SDU’s 8088 processor. It provides the user’s interface to the SDU where it provides…
In my previous installment I tested the Lambda’s fans and the power supply and powered things up for the first time. A few of the fans were non-functional even after cleaning and lubricating and so an eBay order was placed. While waiting for those fans to arrive, I started taking a look at the Lambda’s monitor, referred to in the documentation variously as “High-Resolution Terminals” or…
Last time around I went through the cleaning and inspection of the Lambda. Overall, apart from a few errant screws and a faint musty odor, things looked pretty good. We’re inching closer to the point where we can power this thing on and see what it does, but there are a few things left to go over before we can get there. Power Supplies! We haven’t yet looked at the power supplies in the Lambda…
As mentioned in my last post , the LMI Lambda I acquired spent most of the last two decades in a garage somewhere in Pennsylvania. It wasn’t a climate-controlled garage. It wasn’t a leak-proof or a rodent-proof garage. The door to said garage wouldn’t even close all the way. So this machine was in rough condition when I picked it up. The first thing I did before bringing it in the house was to…
[Editorial note: I originally wrote this series of blog posts for LCM+L's ENGBLG. Since LCM+L is shutting down for the foreseeable future, the fate of ENGBLG is uncertain. I am in the process of translating these posts over to my personal blog in an attempt to preserve this content. - JD] A Tour of my Workspace Like many of you, I’ve been spending most of my time at home these days. While the…
OK, so I've been busy. Very busy. And I haven't posted much. Since the beginning of the year, I've moved into a new house, become a father, worked two concurrent jobs and have somehow remained sane. I've also acquired a number of interesting computers and parts. I've just had no time to play with them and even less time to write about them. Things have settled down slightly -- the move is done,…
Just resting. Seriously, though, I've been insanely busy with a lot of things; not least of all moving to a new house. The good news is I have a lot more space for my computer junk. The bad news is, it takes a long time to move everything. I hope to have everything moved and set up soon, so that Imlac hacking can continue apace...
Sorry for the delay, I've been busy and I've been waiting for replacement parts to arrive. I'll spare you most of the gory details and keep today's post short, since a lot of this is the same old schtick (just a lot of faulty chips that were fortunately easy to trace down) -- but to give you a general idea of what I did over the past week or so, here's a list of the chips I replaced: 5 74H61s 2…
I stumbled on this set of scans over at DigiBarn (a most excellent computer museum), a reprint (in the late '70s) of Imlac's brochures for their systems and configuration options. I thought I'd reproduce some of the text here, since it's pretty interesting (to me, anyway) and since a lot of this is completely new to me -- I've not seen it referenced anywhere. OVERVIEW Imlac Corporation (founded in…
After resolving the issues with the TKA serial port (well, at least in theory until the replacement chips arrive) I turned my attentions to the TTY serial port. Neither transmit nor receive functions were working at all; specifically: Transmitting of data via TPR and related opcodes fails. No data is sent, and the "TTY Output Status" flag (used by the TSF/TSN opcodes) never gets set. Receiving…
Now that I have the Imlac's CPU and memory running well enough to attempt running basic diagnostics, my plan of attack for the rest of the work is roughly as follows: Investigate the functionality of the Imlac's I/O devices, and get them working again where necessary. Use the I/O devices to upload more advanced diagnostics from a PC. Repair remaining CPU issues Repair remaining Memory issues Get…
The Imlac says "Hello" Ehhh, ok, so that's perhaps a bit... unimpressive. You might be asking what the heck it is, in fact -- and for good reason! (You are demanding, but also very astute.) To understand the above, we have to go back. Way back. Back into time . To, oh, three hours ago. I thought it might be fun to see if the Imlac's Display Processor is working at all, and what better way to do so…
After looking at the Power Supply Regulator schematic I decided to live with my hack to the P/S READY signal for awhile and spend some more time debugging the CPU. I'll return to the power supply later ( much, much later ) but for now it runs well enough without it to do some other investigations. Let's see... where did I leave off two months ago before I was sidetracked by the supply issue? Oh…
Well... as it turns out I may in fact have been entirely mistaken about the problem this whole time. I was puzzled by a certain behavior of the front panel, namely that toggling the Read/Store/Continue switches would actually do their associated action about 50% of the time, but "Start" never actually started the system running, even though based on my interpretation of the schematic, once the…