Restoring a vintage 1975 Minicomputer

November 8, 2019

Since August, 2019, when I purchased a Computer Automation Alpha LSI-2 minicomputer on, I have been scouring the internet for information, hardware, and software for the almost forgotten Computer Automation “Naked Mini” Alpha 16 and Alpha/LSI-2 minicomputers from the first computer revolution in the mid-1970’s.

Restoring a 44 year old minicomputer is not for the fainthearted. First, you need to realize that my particular choice for restoration is not the easiest target. Computer Automation has been out of business since 1992. Even though Alpha LSI mini’s were manufactured for nearly 10 years, and tens of thousands were sold, they were mostly used as “components” in other products, and were not well known as stand-alone minicomputers.

It all started with Beginnings…


On the Road to CP/M

September 1, 2021

CP/M and S-100 Systems

Over the past 2-3 weeks I have been unpacking and sorting the computers, S-100 parts and systems I recently moved to my new home in West Los Angeles. I have collected quite a few systems and boards – 3 IMSAI-8080, 2 IMSAI/Fulcrum, Z2-Cromemco, 2 Heath/Zenith H100 series, 2 Northstar Horizon. Several floppy subsystems (5.25″ and 8″), disk controllers, memory, I/O boards. And 2 DEC VT-420 ASCII Terminals. Plus a number of Apple ][, Commodore 64, and Commodore 128 systems. I also have been building some more recent Z80 based single board computers, including the RC2014. And lets not forget the IMSAI-8080 ESP-32 based simulator from Australia (which runs CP/M!). Plus of course my original 3 Computer Automation Alpha LSI-2/20’s.

A few commonalities across all (or most) of these systems  (except for the LSI-2’s ) –

1, They all run (or can run)  CP/M
2.  All support RS-232 serial IO – The Commodores and Apples have video screen graphics and keyboards built in – as does the Heath/Zenith, but they can do serial IO.
3. Almost all are based on the Z80/8080 CPU (except Apple & Commodore with the 6502, but both have Z80 options for CP/M). The Heath/Zenith also has an added 8086 CPU. And the ESP-32 IMSAI emulates Z80.
4. They were all designed and built between 1975 and 1985 (except the SBCs and ESP-32).
5. Many support 2 or more OS’s or runtime environments.

My original project was to restore the LSI-2 system(s) — both hardware and software — to running state. However, I have had a number of obstacles as mentioned below and I was getting frustrated with the slow progress — given my limited time as I still have a full time job. I felt working on 8 bit CP/M systems could help my restoration of the LSI-2 system(s). The big advantage is the wide array of emulators and disk based tools for CP/M, as well as assemblers and debuggers. Plus the ability to develop on a modern PC and then test on the target platform easily.

I have had some difficulty getting software loaded into the LSI-2 and running, even though the hardware seems to work in tests so far.  I do not have original media (paper tape or disks) so everything has to be bootstrapped from scratch, including PC based software loaders from archive formats.  That means coding on DOS and LSI-2 in assembly. It may even mean creating a simple LSI-2 assembler to run on MSDOS.

Therefore, I wanted to restore some of these systems and refresh my memory on 8 bit assembly coding and CP/M and possibly use some of the same techniques on the LSI-2 systems.

Getting a CP/M S-100 System Running

Since I have several goals, I have been using several platforms in parallel to move forward. Most important is to get hardware working first. I now have a working PC Altair emulator running CP/M on Windows 10.  This is a good development environment because it is fast and file transfers between OS’s is easy. I also have a couple of Commodore 128’s working with CP/M and floppy drives. This can be useful because Commodore included the ability to read almost all 1980’s vendors 5.25″ soft sector CP/M disk formats. Osborne, Kaypro, etc. XModem allows me to transfer files to the PC over a serial connection.

The Heath/Zenith H110 system I found recently – which is completely working so far – runs MSDOS, CP/M 80, and CP/M 86 with 5.25″ soft sector floppies. It can also support 8″ drives – a very useful feature.

One of my original IMSAI-8080’s (above photo) was supposed to be running CP/M – but it has Micropolis drives and controller  – which use a pre-standards 100 tpi/16 hard sector 5.25″ diskette format. It is not really an interchangeable format and disks are expensive and hard to find. Same issue with the Northstar Horizon – rare 10 hard sector 5.25″ floppy disks and a very difficult to find or bootstrap implementation of CP/M.

Getting CP/M running on an “normal” S-100 system with 8″ drives was my goal. I had previously spent a few weeks working with the Fulcrum I-8080 replica/clone before my move and had not had a lot of success – again too many unknown issues and variables with ROMs, CPU, Memory, and IO – along with the issues caused by an IMSAI front panel on the bus.

I decided to start over after my move. I took the original IMSAI-8080 that had the Micropolis  drives and removed everything – including the front panel. I wanted to start from scratch and build up the system. I selected a California Computer Systems (CCS) 2810 Z80 CPU card with onboard monitor, and a 64k static ram board that had been in the Micropolis system, and connected a VT-420 ASCII serial terminal to the RS-232 port on the CPU. The board was missing the UART, so I found an INS 8250, put it in the socket and crossed my fingers.  I turned on the power and the CPU status lights came on! Yay! I hit return several times and it worked!!

Note: Apologies for the poor lighting – I don’t have my pro camera and studio lights unpacked yet.

I saw the CCS Monitor sign on – MOSS VERS 2.2

I had a working S-100 CPU and Memory board. With terminal I/O. Finally! A solid starting point for testing and building out the disk system. The monitor allows testing many parts of the system and since I have 2716 EPROMs and a burner, and the assembly source of the MOSS 2.2 monitor, at last I had something to work with. I celebrated and went to bed with much satisfaction.

At my next work session with the system, I decided to do some more testing. I turned the computer on and “BANG!!!” sparks, smoke, and burning parts. One or more Tantalum filter capacitors on the CPU board had given up and released the magic smoke. I turned off all power and looked for burning embers. I was crushed that my working system had died so soon. Also, even with all my vintage computer work, this was the first time capacitors had exploded in my systems.

I had a spare untested CCS 2810 CPU, so I loaded a UART and EPROM copy, checked the jumpers and plugged it in the test system. This time when I turned on the power, “BANG!!!  BANG!!!” sparks, smoke, and more burning parts. The same Tantalum filter capacitors on the CPU board had given up again – this time two of them on first power up. It seems that 40 year old parts do fail sometimes.

I turned everything off and went to my day computer to order new parts from Digikey – Z80’s, dc regulators, and new Tantalum capacitors with higher voltage ratings for longer life. (The yellow ones in the bag are the new ones).

The death toll was 12 Tantalums replaced, a 7805 regulator, and two dead vintage Z80 CPUs. After all the work the first board returned to life, but the untested board still had issues, so it will need extended testing. With a working board available, I can A-B test signals and hopefully get the dead board working quickly.

Dead CCS 2810  Z80 CPU card

Finally, I added the CCS 2822 Floppy Disk Controller card (shown in the chassis above between CPU and Memory). It also has a version of the MOSS 2.2 monitor modified for accessing the Disk controller I/O routines. It uses Phantom to disable the CPU EPROM and overlay the same address space. So it is possible to do a simple board test of the controller by accessing the monitor and issuing a “Boot” disk command. If it hangs (with no drives installed) it is running on the EPROM of the disk controller. If it errors out it is running on the CPU EPROM. I got the error with the controller not installed and after I plugged in the controller I got the “hang”, and if I don’t use the “Boot” command the monitor runs normally on the controller card. So the basic controller seems to work accessing the bus.


I need a bootable CP/M disk with the CCS BIOS for this hardware – I must either make one from an archive image file or find someone who can write a copy disk from their system. Or worst case bootstrap one from an unmodified CP/M using the controller code from other sources and creating a disk api EPROM.

Luckily, once again I met a wonderful Canadian hobbyist from Toronto who offered to make me a CCS boot disk from his system (and a spare Morrow Disk Jockey 2D/B  boot disk as well). This is the third time a Canadian computer hobbyist has helped me on these projects with hard-to-find software. I am just waiting for it to arrive in the mail.

Hopefully in my next post I will have a working CP/M S-100 system running.

A new computer joins the flock

August 17, 2021

Heathkit Christmas Catalog 1984

Recently I was investigating S100 floppy disk controllers as a project to build a fully working S100 CP/M system from one of my IMSAI chassis. I have Commodore 128 and Apple ][ systems that do or can support CP/M. However, my first CP/M systems were Northstar Horizon and IMSAI 8080 with a Disk Jocky 2D/B controller. Most of my experience was with 8″ floppies, except for Northstar which uses 5.25″ 10 hard sector diskettes.

The challenges are

  1. Getting or building a boot disk in the correct disk format with BIOS for the floppy controller card, and system size and configuration (memory and I/O) to load a CP/M system that will work with the particular hardware configuration in the system.
  2. Copying from one format to another – i.e. 8″ to 5.25 inch HS Northstar. Of course files can be moved via serial transfer and load once you have a working system with basic software available.

I came across references to the Z-207 Floppy controller from the H100/Z100 computer system by Heathkit/Zenith. It fully supports 8″ and 5.25″ disks out of the box. So I found a working controller to play with.  I also got a set of OS disks, and discovered the H100/Z100 series supports 3 operating systems – CP/M 85, CP/M 86, and MS-DOS 3 (ZDOS).

This seemed very interesting, so I started learning about the H100 series, a unique 8/16 bit computer which has both an 8085 and an 8086 CPU on the motherboard. The other interesting features are that includes a bit mapped video controller (composite output) and an S100 bus. CPU, I/O, Memory (192kb or 768kb), and video are on the Motherboard and attached video board. Keyboard is built in. Floppy or Winchester HD controller are S100, as are optional add on memory and modem cards.

At Christmas 1984, the Zenith  ZF-111-22 with 192k memory and two 320 kb floppy drives (assembled) and no monitor sold for $3499, with MSDOS. That is $9,193.82 in today’s dollars.

I found an H-111 model in the H100 series from 1984-5 locally in the Los Angeles area with the 768kb motherboard and low profile floppy disks. Including the monochrome amber Heath monitor – Just like the catalog picture above. And it actually works with all three operating systems!!! This version appears to be one of the last models of the H100 made before Heath/Zenith  switched to 16 bit only “IBM compatible” PC models.

The only other widely sold computer I know of that supports both 8 and 16 bit operating systems is the Compupro 8085/8086 CPU S100 card. And it does not perform well on 8085 mode. It supports CP/M 80 and CP/M 86 – but I don’t know if it actually supports MS-DOS.

New HOME for ALPHA LSI-2 systems

July 29, 2021

My move is completed to my new home in West Los Angeles. This house will provide me with the space needed to efficiently work on my several restoration projects including the Alpha LSI-2/20 computers and the IMSAI S-100 computers. I cannot believe how much vintage computer equipment I acquired while living in my previous 2 bedroom condo! Although my new home has a garage, workshop, and 3 bedrooms, it seems like there is no unused space. Well, I guess the answer is that I was squeezed into a much smaller space which made it hard to work on projects.

Of course – I cannot resist the opportunity to restore more systems, so I added a Northstar S100 system recently, and maybe a couple more IMSAI’s.

But back to the Alpha LSI-2 project…  I will be setting up a dedicated work space and 19″ rack for the main system, so I can now begin to load software and test the boards I have. They are all now in one place, and I was surprised how many Computer Automation boards and documentation I have found for the systems. Plus, I will finally be able to unpack and inventory the Alpha LSI-2/20 computer and disks I got from  Bob Rosenbloom’s vintage computer collection in Santa Cruz, CA last year.

IMSAI w/CPA Front Panel vs LSI/2

June 25, 2021

Why IMSAI Here?

I know some folks are wondering why I am discussing a pair of IMSAI computers on a blog primarily about restoring Computer Automation LSI/2 16 bit mini-computers…

Well, here is my logic – both types of systems have “programmer’s” front panels that show what is happening inside the machine, and allow you to stop, start, debug, single step, and input data. Also, the Northstar Horizon and IMSAI 8080 S-100 computers were my second and third computers, in my house, (computers that I actually owned, instead of leased ). The Alpha 16 and LSI/2 minicomputers were the first computers I had possession of – even though they were leased from Computer Automation.

The second reason is that the LSI/2 and IMSAI S100 computers are actually quite similar – except for early S100 systems having an 8 bit data bus and CPU. Therefore, easing back into assembly programming is actually easier on the IMSAI 8080 and Z80 systems because there are a large number of more advanced programming tools – assemblers, debuggers, emulators, etc. that can be run on the hardware, or emulated on a more modern PC system.

Plus, both types of systems were primarily programmed in assembly language. I know, a lot of S100 systems with CP/M ran MBASIC-80 or CBASIC, but for systems programming, it was done in assembly – look at WordStar, Turbo Pascal, MBASIC-80, Modem7, Kermit, Xmodem, and other utilities. All were written in 8080 assembly.

Another bonus is that the 8080 and Z80 systems have tons more documentation readily available on the internet.

Finally, the 8080 and Z80 systems have the capability to run an Operating System – CP/M – on floppy disks or even flash or SD cards. This means that I can relearn my skills with less friction and pain, then apply them to the LSI/2 which has more a primitive work environment, at least until I can get some floppies working and disks rebuilt.

So am I backing out of the Computer Automation LSI/2 restoration? NO! In fact, since I am moving soon, I have decided I need a new place with enough space to set up all of my vintage systems and be able work on them in parallel – including the THREE LSI/2 systems I own.

IMSAI Restore continued…

So how are the IMSAI’s doing? Well, after replacing the Z80 in my Fulcrum I8080 with the Jade Z80 CPU, I was able to see some functionality from the CPU. However, depositing data and viewing memory still didn’t work correctly. However, now I could read the boot EPROM in the Jade board correctly.

Next step was to see if it was the CPU, the memory, or the CPA front panel causing issues.

I built a replica IMSAI CPU-A board with an 8080-A CPU as the simplest CPU card that should absolutely work with the front panel. It mostly ran, but I still could not write to memory. So I decided to re-chip the front panel.

By the way, it is a Fulcrum replica version of the IMSAI CPA front panel PCB in the Fulcrum branded IMSAI. This version was re-laid out (with tape) from negatives of a bare original CPA, with all of the IMSAI fixes applied. I should know – I did the tape up myself at Fulcrum in 1981. I was hoping that either corrosion or bad flip-flops or one shots was the cause of the write problem. But no luck. Time to break out the scope.

I also got some advice from the retro forums about some S100 lines that might be grounded on the Jade CPU or CompuPro memory boards that could prevent memory writes. At this point I am fairly close to being able to run code on the system. But, I had to stop work because of the pending move to a new home. More coming soon.

IMSAI Updates

June 23, 2021

IMSAI Systems Restoration

As I mentioned in my previous post, I recently acquired two IMSAI 8080 computers – one original and one Fulcrum i-8080 vintage 2nd generation. My goal was to get them running and then have CP/M running on both of them. The original IMSAI came with Micropolis 5.25 inch floppy disk drives and controller and may boot when I get it working. The Fulcrum I-8080 came with a Jade Z80 S100 cpu and Morrow Disk Jockey 2D/B floppy controller, and a Morrow Thinker Toys Wunderbus motherboard. It also had a Fulcrum VIO-X video card.

I started working on the Fulcrum I-8080. The first issue was there was no memory in the system. Dusting of my ancient S100 memories, I decided to try to find static RAM boards for the system on eBay. There is more S100 memory than any other board type on eBay, but a lot of it is dynamic or off brand stuff. I found some CompuPro RAM 16 which I thought was a good deal – 32KB boards using 6116 static memory. I ordered a couple. Then as I was doing more research I discovered that many CompuPro RAM boards were difficult to use in older S100 systems like the IMSAI. They were compliant with the IEEE S100 standard while older system boards may be “pre-S100 standard” IMSAI or Altair bus interfaces with some bus lines used differently. The IMSAI front panel could also be an issue with some memory. The Vintage/Retro Computer Forums had notes about how to modify the RAM 16 to work with IMSAI style boards but it is a pain. So I found some CompuPro RAM 20 (RAM XX version) boards that have more options exposed and are easier to configure. I also got a replica Jade Bus Probe board and an S100 extender card to help with debugging.

Now I had the boards for a running system (if they worked!!).  I tested the Fulcrum power supply and the voltages looked good. In the S100 system the linear unregulated power supply provides high current DC voltages to each board and the board is responsible for regulating the voltages to +/- 5 VDC and +/- 12 VDC as needed. This uses a lot of power and generates some heat. Vintage S100 RAM boards are especially power hungry. The RAM 20 has FIVE 7805 regulators on the board.

I installed the Jade Z80 CPU, the Bus Probe,  and a memory card. When I applied power, the bus probe and front panel lit up. However the front panel switches did not have the expected results. The computer did not enter run regardless of switch inputs. I used an extender card and my Sigilent SDS1104X-E 4 channel oscilloscope. The M1 signal was not pulsing. The CPU clock oscillator was running. Reset was working. I decided to replace the Z80 CPU first. Voila! The CPU runs now. There are still other issues, but this is a good start.

One of the blue panel switches  (C&K 7113) paddle is missing, but I was able to find a couple of new matching replacements in Australia. These switches and paddles have not been manufactured for many years and are one of the hardest parts for restorers to find.  Fulcrum could not get the darker blue switch paddles that IMSAI used (they were custom made for IMSAI) and Fulcrum’s blue paddles were lighter as you can see in the photos in my original post. Unfortunately, these new paddles are lighter blue than Fulcrum’s blue paddles and do not match the other switches. It works but I will have to keep looking.

IMSAI 8080 Computers

April 9, 2021

As if I don’t have enough projects to work on, I recently acquired two IMSAI 8080 vintage computers. The IMSAI 8080 was the “second” widely sold 8-bit personal microcomputer using the Intel 8080 microprocessor and was released in late 1975 – a few months after the MITS Altair 8800. In 1976, they advertised a “system” for $621 assembled (almost $3,000 in today’s money). That included the steel chassis, a pre-S100 backplane and hefty power supply, switch & led front panel, an 8080A CPU card, and 256 bytes of memory on a 4K RAM board. At this time Intel was selling just single 8080 chips for around $350.00.

It was later available with the more powerful Intel 8085 and used the Altair 8800 backplane/bus design which later became the basis for the S-100 standard. The IMSAI products were  made in San Leandro, CA (Silicon Valley) by IMS Associates Inc. (IMSAI). It is estimated that IMSAI sold between 15,000 and 17,000 computers and kits.

The 8080 was sold mostly in kit form. There eventually was a full line of IMSAI personal and “business” computers. However, as more companies entered the S-100 market selling products and kits for less than IMSAI, the market became too competitive. IMSAI was unable to grow the business market quickly, leaving only the slick home/gaming computers like Apple, Atari and Commodore in the running against the S-100 hobby computers. IMS Associates Inc. went bankrupt in October 1979 and the assets were sold at auction.

I owned two IMSAI computers in the 1980’s, both of which I built myself from parts sourced in Silicon Valley surplus stores. An electronics surplus store in San Jose, CA purchased some of the assets of IMSAI at the auction and sold parts and complete IMSAI kits for several years. They also manufactured new products, including new S-100 boards and replica IMSAI 8080 systems using some of the original designs and parts under the name Fulcrum Computer Products.

I worked at that electronics store in San Jose for a year or so during the time when they were selling IMSAI parts and systems and the Fulcrum products. Part of the work included updating original IMSAI PCB designs (hand taping from photo negatives) for the front panel and other boards to include fixes and updates and development of some of the Fulcrum products — including documenting their VIO-X intelligent video terminal S-100 board and their 8″ CP/M 2.2 distribution.

Although there were a number of microcomputer “floppy disk operating systems” developed in the early days of personal computers, by far the most successful was Digital Research’s CP/M. It was first used on the IMSAI, and later was available on virtually every 8-bit computer made in the 1970’s and early 1980’s – even the Commodore 128 and Apple II (with Z80 board). While it was primitive and had limited storage compared to today’s disk systems – it was far better and faster than paper tape or audio cartridge tape solutions. It allowed these computers to be used for more demanding applications like word processing, data bases, and programming.

Later, I used these computers running CP/M 2.2, DB2, Turbo Pascal and WordStar for several years for programming and word processing. I actually wrote and published three computer books and hundreds of market research and magazine articles with these tools.

So back to the present… I acquired two IMSAI 8080 systems and one was original IMSAI, while the other was a Fulcrum “updated replica” I-8080 system. The original IMSAI 8080 looks to be in good shape and has two Micropolis 5.25″ floppy drives and controller for CP/M 2.2. The Micropolis drives use a pre-standards 5.25″ floppy disk format of 100TPI and 16 hard sectors. Shortly after Micropolis released their system with proprietary controller and drives, the industry standardized on soft sector 96TPI formats for 5.25 inch floppies (except for Northstar). Micropolis written disks can only be read on Micropolis floppy drives.

The Fulcrum I-8080 I found has no memory or drives, but includes a Jade Big-Board Z80 CPU (rev C), a Fulcrum VIO-X and Morrow Designs Disk Jockey 2D/B floppy disk controller. It also has mostly original IMSAI chassis metalwork, and the Fulcrum updated replica IMSAI PS28D Power Supply,  a Morrow Thinker Toys 20 slot active terminated Wunderbus, and an updated replica IMSAI CPA front panel.

I have decided to use 8″ floppies and maybe add an IDE Flash drive upgrade later. I also found a pair of Shugart 801 drives in a rack mount panel. I got some Compupro RAM-XX and RAM-20 32k static ram cards for this system since it does not have any memory.

Unfortunately, one of the powder blue panel paddle switches (C&K 7113) is missing, but I was able to find a couple of new matching replacements in Australia. These switches and paddles have not been manufactured for many years and are one of the hardest parts for restorers to find. However, I have just found a similar switch from Mouser made by NKK. (Update: Read the dimensions!! The switches Mouser had in stock were “miniature paddle” switches and were about 1/2 the size of real IMSAI switches. Doh!!)

For some reason I have always been fascinated with vintage computers that feature front panels with status lights and input switches. I think it may be because all of the computers I used in the early part of my career (1960s & 1970’s) were either IBM mainframes or minicomputers with these features. When microcomputers first became available, they used the same lights and switches front panel I/O approach due to the high cost of other options.

I really love to watch the CPU “at work”!

After doing some research to refresh my memory about how to get S-100 computers up and running with CP/M 2.2, I found lots of code from the RLEE archive for the Morrow Disk Jockey 2D/B floppy controller, but no prebuilt 8″ floppy disk images to use for CP/M. I decided to add a CompuPro Disk 1 board to use to bootstrap the DJ card and build a new image for CP/M. I also was able to find some 8″ IMD images for the Disk 1 system, and even a set of  CompuPro original system disks. So that is my current plan to get the Fulcrum I-8080 running with CP/M again. I even have an Adaptech  Aha-1522 ISA controller  which can be used with Dave Dunfield’s IMD utility to write 8″ disks from an older IBM PC. I am looking forward to a  nostalgic and fun weekend of  building a CP/M image.

4/20/2021 – UPDATE: I have found two Canadian collectors online who have worked with the Disk Jockey 2D/B controller and CP/M 2.2. One has built a bootable disk from scratch (in 2012) for his IMSAI and featured it on his YouTube channel. It was quite a project. (IMSAI 8080 8″ floppy disk drive project in preparing for CP/M PART 1)

The other collector was posting on a vintage computer newsgroup and mentioned he had a DJ 2D/B. I asked him if he could share a boot disk image and he was nice enough to offer to send me an actual disk.

Spring Update 2021

April 9, 2021

I have survived the COVID-19 Pandemic so far, now a full year in self isolation (only leaving my home for food shopping and Dr. appointments). Luckily I have a nice view of the Pacific Ocean about 1/4 mile away, since I live in West Los Angeles. I was lucky to get both my COVID-19 vaccinations (Moderna) in February and March 2021 and had minimal side effects (headache and fatigue). I have also been very fortunate that I was able to keep working through the whole lockdown, and my employer has been able to maintain its profitability during this time.

While I have continued to add to my Computer Automation LSI-2/20 systems with some more acquisitions from eBay, I have not had as much free time as you might expect because my day job has been quite busy and has required a lot of off hours work to keep up with the business needs. Success has its costs as well as benefits.

I plan an update in the next few weeks with some major progress on the system functionality. I have also started a few enhancement projects including a remote hex key pad to augment the front panel input keys, similar to the programmers panel on the later LSI-4 systems. I have also been working on software support systems like a cross assembler and file uploader.

So I apologize for not having more  updates on the restoration process, but hopefully there will be some more good content coming soon.



Christmas update December 2020

December 24, 2020

Well, time flies when the world is a crazy place!! Between “stay at home/work at home” orders and the unrest caused by politics and economics this year, time has flashed by like DVD on fast forward.

My day job has been very busy and has not left me much time for working on my passion project/hobby of restoring the Computer Automation LSI/2 minicomputers I have acquired.

The Good, The Sad, and the Ugly

The good is that:

  1. I found a new-in-box portable Remex RAR-5200 paper tape reader punch (serial and parallel)
  2. I have found a collector in Europe that has documentation for several of the cards below
  3. I have found some of the very scarce I/O boards including:
    • Utility I/O (parallel printer and high speed paper tape interface)
    • dual TTY module
    • 16 bit I/O
    • 64 bit TTL input card
    • transport interface – for 9 track IBM compatible tape drives like Kennedy 9000 and Pertec (both of which I used in my 1973 project) (no docs)
      1. requires a tape formatter
      2. requires a 9 track drive (and a strong back – very heavy)

“Regrets, I’ve had a few…”

Naked Mini LSI-4/90

The sad news is that I didn’t buy the full rack Naked Mini LSI-4/90 System that was offered on for $1800.00 plus $850.00 shipping.

Although I could have purchased it, I was concerned that I have never found ANY hardware documentation on the LSI/4 systems or the hard disk storage they used. I love the way it looks, but I would have probably had to scrap all of the peripherals and rack cabinet due to lack of space where I live.

ASR 33 Teletype

I also did not buy the used ASR 33 Teletype that was for sale in a lot locally earlier this year. It was actually a TWX machine plus two Model 32 Telex machines. Again, I was concerned about space, but I should have done the deal – it was only $300 for everything. Just a used ASR 33 sold on eBay a month later for over $1000.

1920’s Amateur Radio Station

HAM it up!

Growing up, one of my favorite pastimes was listening to short wave radio. In those days (the 1950’s and 60’s), there were many old multi-band “console” radios from 1940’s and 50’s available for nothing. Most people were watching the TV, not listening to radio in the evenings. I listened to foreign stations, Morse code, “satellites” like Sputnik and even distant “clear channel” broadcast stations at night – some were hundreds of miles away.

When I was about 14 living in the Seattle, Washington area, I met a neighbor who was an amateur “HAM” radio operator. He was kind enough to explain how short wave radio worked to a curious and persistent kid. I tried for several years to learn Morse code so I could get my license, but I was not able to. I had a CB license, and later got an FCC Radio Telephone Third Class License with Broadcast endorsement so I could operate the 1000 watt FM radio station transmitter (KSPC-FM) at my college, but I never got my amateur (HAM) license.

A few years ago in Dec 2006,  the FCC removed the Morse code requirement for Amateur Radio. In September,  2020, I passed my Technician Class Amateur license. In October,  2020, I passed my General Class Amateur license. and in November,  2020, I passed my Extra Class Amateur license.

I now have an Amateur Radio License after 55 years! I am now W6NF (Whiskey Six November Foxtrot) and have the highest class Amateur license currently available.

ICOM IC-7300 Digital HF Amateur Radio Transceiver

Finally, my Christmas present arrived from the North Pole – a new ICOM 7300 SDR radio to use to explore my new ham privileges. Don’t let the small size fool you, this radio is the most full featured entry level rig ever offered and it is a totally digital radio. It does SSB, CW, DATA, and even the old school AM modes.

Once I was able to get an antenna up at my apartment, I was amazed at the contacts I was able to make using the new digital data modes like FT8. In one evening I had over 20 contacts from all over the world including USA, Canada, Hawaii, Alaska, Mexico, Chile, Argentina, Greece, Russia, China, Japan, and New Zealand. My signal was even received over 10,000 km away in Antarctica!


Naked Mini LSI-4 and More

October 4, 2020

October 2020 has just begun and several of my vintage mini-computer dreams have come true!

Alpha 16 Front Panel

First, I just found and bought a real Computer Automation Alpha 16 front panel from 1971 online. Believe it or not, the Alpha 16 minicomputer was the first computer I ever “owned”, or even had in my possession. In about 1972, I was working as a telecommunications engineer for Arcata Communications (one of the first private business telephone “interconnect” companies) located in the SF Bay area. I was asked to design a phone call billing system for use with a private phone system, to log calls for hundreds of phones in a business.

I proposed a solution using the Alpha 16 computer as a controller, but the company decided they didn’t want to develop and build hardware. So they released the idea to me. I partnered with a college buddy and we “leased” an Alpha 16 from Computer Automation. I developed the product idea to prototype stage in my two bedroom apartment, learning assembly programming in the process. I used a Teletype ASR33 as the console and paper tape I/O for storage.

Months later, the company approached me and offered to buy the design, which I gladly agreed to. I worked on the product for several years and it was deployed to a number of large customers. We actually used the later release Alpha LSI-2 for the production machines.

Naked Mini LSI-4/90 System

Although I never used a Naked Mini LSI-4 computer, I always wanted one. The design was so cool and very unique, with the hex LED displays and the keypads for entry. The LSI-4 was also hardware compatible with the LSI-2 but had a much upgraded architecture. It supported 64K words of 16 bit memory instead of 32K, it had multiple registers, stack operations, and more instructions (of course). There was a 9 slot chassis version with separate power supply. Plus it was faster.

I recently found an LSI-4/90, the top end model. It was used by Delco Electronics in a software development role for designing military aircraft firmware. It is on my wish list for Christmas.

High Speed Paper Tape Reader Punch

Another item on my bucket list for the Computer Automation LSI-2 restoration project has been a paper tape I/O device. I had an opportunity to buy a lot of used Teletype ASR-32 (Telex)  and ASR-33 (TWX) units but I was too slow/cautious to make a quick offer and I missed out on the deal.

Remex RAR-5200

Recently, I found a New-Old-Stock (NOS) (in the box) Excello-Remex RAR-5200 portable reader punch. It runs at 200 cps (reader) has both a serial and parallel data interface. It should be easy to interface to the LSI-2 serial port. It even has a full tech manual.

I at the same time, I was able to find some NOS mylar 1″ punch tape stock and some standard oiled paper tape as well. I also found a REMEX RRS9000BA1 “Director” paper tape reader for a great price.

I hope to use one or both of these devices to punch and load the standard paper tape software tools library binary images I have from the Internet Archive.

Sadly, I have been unable to find a Computer Automation parallel utility I/O board which was the standard interface for printers and paper tape readers, or a Computer Automation parallel distributed “Pico Processor” I/O module either. [FLASH UPDATE: Check out the December 2020 Christmas post – I found a parallel Utility card! ]

Computer Automation, Inc.

July 5, 2020

Computer Automation, Inc. was a computer manufacturing company originally based in Newport Beach, California that built minicomputers from the 1967 to 1992. The company moved to Irvine, CA in 1973. It was founded by David H. Methvin, who conceived and designed the original PDC-808 minicomputer. This 8-bit computer was sold as a Programmed Digital Controller, because the purchasing departments of some companies made it difficult to buy a “computer.”

Computer Automation PDC-808 (Courtesy Computer History Museum)

Alpha 16 Minicomputer

In 1969, Computer Automation developed the Alpha 8 and Alpha 16 line of 8 and 16 bit minicomputers. The Alpha 16 was very successful, but was a fully discrete logic (DTL/RTL/TTL) minicomputer. The processor, ALU, and registers took up three full 15″ x 17″ circuit boards (with up to 168 ICs per board) and used a lot of power.

The Alpha 16 was possibly the first minicomputer specifically designed for OEMs (Original Equipment Manufacturers) to be used inside another product.

The “Naked Mini” – The computer that’s a component.

Computer Automation created a “naked” minicomputer costing less than $1500 (in quantity) designed for use in embedded systems. The Alpha 16 became the first of the “Naked Mini” products,  a line of cheap, easy-to-use, reliable minicomputers “designed as a dependable component ready to bury into your system.” Engineers eager to “computerize” their products loved it. Their advertising tag line was “The computer that’s a component.

Alpha/LSI Minicomputer

Integrated circuit technology was developing very fast with higher levels of integration on chip. To reduce costs and remain competitive, Computer Automation soon began developing the Alpha/LSI product line.

The Alpha/LSI series of machines used increasingly more MSI and LSI components to reduce size, power, and heat, and increase the speed of the systems. The Alpha/LSI-2 was the first high production member of the family, and was manufactured from 1973 to 1985. It also had a fully micro coded processor on ROMs which enabled a large and powerful instruction set. There were several models released that were successively more powerful.