View Full Version : 1982 British built LSI M-THREE computer restoration project

September 8th, 2015, 01:12 PM
Iíve been slowly renovating an early 1980s British built computer that I acquired this year and thought itís high time I posted a few pics here. The system in question is an LSI M-THREE/250 computer - itís a bit of an ugly duckling, but itís also one of the first business class machines I used whilst on an IT based youth training scheme.

When I got it, it was in poor condition after being stored in a loft (attic) for 20+ years.


Hereís a close up of LSI M-THREE screen showing the breakdown of the bonding material between the CRT and safety lens. Fortunately, it wasnít difficult to remove the safety lens.

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=26457&stc=1 http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=26458&stc=1

This is the inside of LSI M-THREE fascia, prior to cleaning. A date stamp of 11 March 1982 can be seen on the drive zero bay - unfortunately, this washed off during the cleaning process :(


This is the main board prior to cleaning. Most chips appear to be date coded 1981. The EPROM labelled 033 holds the MC6845P CRT controller character font and the one labelled 034 holds the bootstrap loader prom. The empty socket is where the hard disk drive handler prom would reside in a Winchester model machine. As I later discovered, it turns out that the hard disk drive handler prom socket is a handy place to install a monitor prom :-)


Five's the limit, so more pics in the next post...

September 8th, 2015, 01:19 PM
Here we have the massive keyboard uncovered. Itís basically as wide as the system unit and connects via a 25way cable. Also of note is the piezo buzzer on the keyboard PCB - the only source of sound from this machine (other than the fan and the two floppy drive motors constantly running).

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=26461&stc=1 http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=26462&stc=1

This is the system cleaned, power supply repaired (cleaned and all paper capacitors replaced) and re-assembled. The dark shadow around the left and top of the screen is due to the safety lens not yet being fitted.


As Iíve already mentioned, the machine has a socket for a hard drive prom. From disassembling and commenting the boot/bios prom I found that if it detects the presence of a hard drive handler prom it prompts to boot from floppy rather than just booting directly from floppy. Any response other than ĎYí causes it to jump to the hard disk prom. So thatís where I placed my monitor.

http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=26464&stc=1 http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=26465&stc=1

Reachedthe limit again, just a couple more pics to come...

September 8th, 2015, 01:27 PM
Iíve also noted the mainboard component layout and chip/socket identification details.


I've also got the operators manual which lists all models in the LSI M-THREE range including their specifications. I've scanned it and will look at getting it uploaded somewhere (I'll check with Al over at Bitsavers),togetherwith the EPROM dumps and my monitor prom source.


Next steps, write my own flavour of CP/M for this machine. Also thought of adding a hard drive, based on something like Jamesí lo-tech TRS-80 adapter, but plugging directly into the Z80 socket via a shim wire wrap socket/board.

September 8th, 2015, 01:57 PM
What is the unpopulated part of the PCB? Perhaps you could hook in there.

September 8th, 2015, 02:06 PM
Great work with the restoration! When I saw the first photo I thought it was a luggable like the Osborne/Kaypro. Didn't realise they were 8" drives!! :)

September 8th, 2015, 02:14 PM
The unpopulated section is for an optional IEEE 488 GPIB circuit. As the silkscreen lists the missing components, I was contemplating whether to add them or not, hence my thought of attaching a hard disk adapter (using a CF card) directly to the CPU socket.

September 8th, 2015, 02:18 PM
Yeah, you could say it's a bit bigger than an Osborne or Kaypro - The width is just over 25 inches and it weighs around 78 lbs (most of the weight is down to the SA-851 drives).

Rick Ethridge
September 8th, 2015, 07:18 PM
Very classy!

September 8th, 2015, 07:23 PM
That is a good looking beast of a machine now that you've done some cleaning. Have you put it on a scale? Just looking at it, I'd guess 50-60 pounds.


September 9th, 2015, 12:09 AM
Have you put it on a scale? Just looking at it, I'd guess 50-60 pounds.

No, I've not weighed it, but I've just double checked the operators manual and it states this model with keyboard as coming in at 77 pounds.

September 13th, 2015, 01:06 PM
A nice restoration of a classy machine. Well done!

January 29th, 2017, 07:42 PM
Impressive work.

January 30th, 2017, 01:55 PM
Impressive work.


Since this was first posted, I've written a CP/M 2.2 CBIOS for it that makes use of the 36 programmable function keys, patched CP/M to use the ZCPR CCP replacement and have it running with a HxC floppy emulator (which is much quieter than the two Shugart 8" drives). Next steps are to add a simple 8 bit IDE interface and patch my monitor prom to allow booting directly from IDE HD or SD card and re-writing the LSI utilities mentioned in the LSI M3 Operations manual (http://bitsavers.trailing-edge.com/pdf/lsiComputers/LSI_Computers_M3_Operations_Manual.pdf).

Booted into CP/M 2.2 with ZCPR:

Programming the function keys:

And why not, playing Aliens :)

January 30th, 2017, 02:57 PM
That's a fantastic job, well done! I had forgotten about LSI - didn't they have an OS called Elsie, or something?

A date stamp of 11 March 1982 can be seen on the drive zero bay - unfortunately, this washed off during the cleaning process :(

This is just me and others may disagree but, as you have photographic proof of the original date stamp, I don't think that it would be unethical to replicate it. That looks like it was done with a bog standard date stamp, so it should be easy to do. You could tape a piece of paper next to it that read "Replica of original stamp which was lost during cleaning" if you had any concerns.